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The Role of Bacterial Interference in Otitis, Sinusitis and Tonsillitis
Otolaryngology–Head and Neck Surgery (2005) 133, 139-146
REVIEW
The Role of Bacterial Interference in Otitis, Sinusitis and Tonsillitis Itzhak Brook, MD, MSc From the Department of Pediatrics, Georgetown University. Bacterial interactions that include antagonism (interference) and synergism help maintain balance between the members of the normal endogenous flora. Alpha-streptococci that predominate in the normal respiratory tract flora attracted most attention in studies of bacterial interference. Other organisms that possess interfering characteristics in upper respiratory tract infections (URTIs) are nonhemolytic streptococci, and Prevotella and Peptostreptococcus spp. The production of bacteriocins by some microorganisms is one of the important mechanisms of interference. The role of bacterial interference in the development of URTI and its effect on the eradication of these infections is discussed. These infections include pharyngo-tonsillitis, otitis media, and sinusitis. Treatment with various antimicrobial agents can affect the balance between members of the oro-pharyngeal bacterial flora and interfering organisms. Implantation into the indigenous microflora of low virulence bacterial strains that are potentially capable of interfering with colonization and infection with other more virulent organisms has been used in preliminary studies as a means of coping with the failure of antimicrobials in the treatment of several URTI. © 2005 American Academy of Otolaryngology–Head and Neck Surgery Foundation, Inc. All rights reserved.
Bacterial colonization of the mucous membranes is initiated in the newborn immediately after delivery.1 The process of colonization of mucus membranes evolves competitive interactions between the various micro-organisms. Bacteria interactions occur when micro-organisms compete to establish themselves and dominate their environment. Some of these interactions are synergistic while others are antagonistic, as organisms can interfere with each other’s growth and compete for their ecological space. Bacterial interference (BI) can have a major role in maintaining the normal flora of skin and mucous membranes by preventing Reprint request: Itzhak Brook, MD, MSc, 4431 Albemarle St, NW, Washington DC 20016.
colonization and subsequent invasion by potential pathogenic bacteria (Fig 1). This phenomenon is most important in preventing certain bacterial infections. Several mechanisms account for BI. One proposed mechanism is that the normal bacteria occupy certain sites on the epithelial surface cells and thus prevent pathogens from adhering to these cells.2 Other mechanisms includes changes in the bacterial microenvironment, the production of antagonistic substances by some bacteria, and competition for needed nutritional substances.3,4 The mediators of BI include bacteriophages and the production of complex materials by micro-organisms such as bacteriocins or bacteriolytic enzymes and less complex molecules such as hydrogen peroxide, lactic, or fatty acids and ammonia.3,4 Bacteriocins are bactericidal proteins that are generated by bacteria and are extracellular toxins that selectively kill other bacteria and promote colonization.5 Unlike traditional antibiotics, some have a broad spectrum while others possess narrow spectrum of activity and only kill bacteria of the same or closely related species.6,7 The strains producing a bacteriocin are generally resistant to the bacteriocins they produce. The mode of action of bacteriocins with larger molecules is through adsorption to their specific outer membrane receptor that is present on the susceptible cells. They are thereafter translocated to their specific target(s) within these cells.8 This is followed by significant biologic and morphologic changes in the targeted bacterial cell and probably also in the bacteriocin particle. The recent worldwide emergence of increasing resistance to antimicrobial agents has generated interest in BI as a means of controlling the problem. This approach evolves substituting the use of antimicrobial therapy with artificial E-mail address: [email protected].
0194-5998/$30.00 © 2005 American Academy of Otolaryngology–Head and Neck Surgery Foundation, Inc. All rights reserved. doi:10.1016/j.otohns.2005.03.012
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Figure 1 Role of normal flora in preventing colonization and subsequent infection by pathogenic bacteria.
implantation into the indigenous microflora bacterial strains of low virulence that are potentially capable of interfering with colonization and subsequent infection with more virulent organism(s). Antibiotic therapy can also affect the balance between pathogens and normal flora by disrupting the ecological balance thus facilitating recurrent upper respiratory tract infections (URTI). Alpha-streptococci (AHS) that predominate in the normal respiratory tract flora have attracted the most attention in studies of bacterial interference.9 Most AHS can produce bacteriocins.7,8 Other organisms that possess interfering characteristics in URTI are non-hemolytic streptococci, and Prevotella and Peptostreptococcus spp.10 This review is focused on the role of BI in the development, prevention and eradication of URTI.
STREPTOCOCCAL PHARYNGOTONSILLITIS The failure of penicillin therapy to eradicate tonsillitis caused by Group A beta hemolytic streptococci (GABHS) is of great clinical concern. In a recent study,11 more than 35% patients treated with oral penicillin V and 37% of benzathine penicillin G-treated patients were microbiologic treatment failures at either 10 to 14 or 29 to 31 days after therapy. Various theories have been offered to explain this phenomenon. One is that beta-lactamase-producing bacteria (BLPB) can “shield” GABHS by inactivating penicillin. BLPB were recovered from over 75% of the tonsils of patients who had tonsillectomy for recurrent infection.12 Another explanation is that interfering organisms such as AHS that are part of the normal oral flora are missing in many of those patients who fail penicillin therapy.13-16 These AHS play an important protective role in preventing colonization and subsequent infection by GABHS and their absence may lead to failure of penicillin therapy.13
Clinical Evidence for BI The interactions between GABHS and other bacteria in the oropharynx have been studied over the past 30 years. Crow et al14 demonstrated that children who subsequently became colonized with GABHS were less often colonized by flora inhibitory or bactericidal for GABHS than those who did not become colonized with these organisms. Sanders et al15
showed that oral therapy with penicillin (and to a less extent with tetracycline) induced a decline in the number of interfering organisms, a decrease that lasted for at least 21 days after therapy. Sanders et al16 found that interfering bacteria are more often isolated during the months with the highest prevalence of GABHS infection and that the prevalence of bactericidal organisms increased with age, probably contributing to the resistance of older individuals to streptococcal infections when compared with children. The organisms with the greatest inhibitory capacity were AHS, non-hemolytic streptococci, and Neisseriae species. AHS can inhibit the colonization of a variety of pathogens such as Streptococcus pneumoniae, GABHS, and Staphylococcus aureus in patients as well as in vitro. Their production of bacteriocin and other inhibitory substances may explain this phenomenon.13,14,17,18 Suppression of some bacterial growth may also occur through utilization of nutrients in the nasopharyngeal environment essential for the colonization by potential pathogens.19 Dajani and Wannamaker20 found that many strains of AHS could produce bacteriocin. These inhibitory substances have been called viridins and one of these (viridin B) has been partially purified and characterized.21 This bacteriocin (and apparently other viridins as well) is inhibitory against Gram-positive as well as Gram-negative bacteria. GABHS also harbors an inhibitory capability through the production of peroxide as well as a bacteriocin, designated Streptocin A or streptococcin A-FF22.22 Beck23 observed a high interfering capability of a Streptococcus viridans strain isolated from an individual who was resistant to acquisition of infection with GABHS. This strain inhibited completely 72% and partially 28% of the GABHS tested. Beck suggested the “implantation” of this strain to patients with recurrent infections of GABHS as a method of preventing recurrences. The tonsils of patients with recurrent streptococcal pharyngotonsillitis harbor less AHS with interfering activity against GABHS compared with healthy individuals.24,25 Grahn and Holm26 found an increased resistance toward recurrent GABHS throat infections in family members with high numbers of interfering AHS in the throat flora as compared with those who lacked such AHS. Roos et al19,24 found that patients with recurrent GABHS pharyngotonsillitis lacked interfering AHS more often than healthy relatives who were carriers of the same type of GABHS. Roos et al24 and Brook and Gober27 showed that both production of beta-lactamase by the normal oropharyngeal flora and the lack of colonization of the pharynx by inhibiting AHS were associated with the failure of penicillin to cure GABHS tonsillitis. The role of aerobic and anaerobic organisms other than AHS in interfering with GABHS growth, was evaluated in a study by Brook and Gober.28 The authors compared the frequency of recovery of aerobic and anaerobic bacteria with interfering capability for GABHS from the tonsils of
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The Role of Bacterial Interference in Otitis. . .
141
Table 1 Recovery of organisms with bacterial interference capabilities in children who are prone to infection and not prone to infection. Number of interfering organisms/individuals (average per individual) Infection type
Site cultured
Otitis media
Adenoids Nasopharynx Nasopharynx Nasal cavity Tonsils
Sinusitis Tonsillitis
Prone to infection 26/25 22/20 27/20 13/20 11/20
(1.04) (1.1) (1.35) (0.65) (0.55)
20 children with and 20 without the history of recurrent GABHS pharyngo-tonsillitis (Table 1). Eleven aerobic and anaerobic isolates with interfering capability for GABHS were recovered from 6 (30%) of the 20 children with recurrent GABHS, and 40 such organisms were isolated from 17 (85%) of the 20 without recurrences (P ⬍ 0.01). The interfering organisms included aerobic (alpha and non-hemolytic streptococci), and anaerobic organisms (Prevotella and Peptostreptococcus spp) The study illustrates that the tonsils of children with the history of recurrent GABHS infection contain less aerobic and anaerobic bacteria with interfering capability of GABHS than those without that history. It also suggests that the presence of these interfering bacteria may play a role in preventing GABHS infection.
Therapeutic Use of BI in Tonsillitis The first attempts to recolonize the throat with bacteria isolated from the normal flora to avoid overgrowth of pathogenic bacteria have been presented by Sprunt and Leidy.29 A series of 4 studies from Göteborg, Sweden30-32 evaluated the use of inoculation of the nasopharynx with interfering AHS, in the prevention of recurrent GABHS pharyngotonsillitis. This approach was used because patients treated with antibiotics often have a disrupted pharyngeal flora and may lack AHS that possess interfering activity against GABHS. The first study was open and nonrandomized and included 31 patients with recurrent streptococcal tonsillitis that were given antibiotics for 10 days.30 At the end of therapy, the patients mouths were sprayed with 4 selected AHS strains known to have strong in vitro growth inhibiting activity against most GABHS. After AHS treatment, none of the patients contracted a new episode of tonsillitis during the follow-up period of 3 months; 8% of a group of patients who did not receive AHS had a second tonsillitis. The second study was double-blind, randomized, and placebo-controlled.31 Thirty-six patients with recurrent GABHS tonsillitis were treated with antibiotics followed by mouth spraying with either placebo (19 patients) or a pool of 4 selected AHS interfering strains (17 patients). None of the patients in the AHS-treated group experienced a recur-
Not prone to infection 63/25 57/20 76/20 41/20 40/20
(2.52) (2.85) (3.8) (2.05) (2.0)
Reference number 41 41 54 54 28
rence during the first 2 months of follow-up, but 7 in those treated with antibiotics and placebo did (P ⬍ 0.05). After 3 months, only 1 patient in the group treated with AHS and 11 in the placebo-treated group had a recurrence. The third study32 was a randomized, placebo-controlled, double-blind, multi-center one. A total of 130 patients with recurrence of GABHS and clinical signs of pharyngotonsillitis were enrolled. The patients received antibiotics for 10 days, followed by 10 days of AHS-inhibitory to GABHS or placebo spray therapy. The clinical recurrences (bacteriologically verified) in the AHS- (n ⫽ 51) and placebo-treated (n ⫽ 61) patient groups were 2% (n ⫽ 1) and 23% (n ⫽ 4) respectively, in patients given spray (P ⫽ 0.004). The inclusion of “early treatment failures” reduces this difference (P ⫽ 0.064). The authors concluded that AHS given as a spray and used for at least 5 days significantly prevented recurrence of GABHS pharyngotonsillitis. The fourth study33 was randomized and placebo-controlled and included 342 patients with tonsillitis but did not focus on individuals with recurrent episodes of infection. A significantly lower number of recurrences was also found in patients with nonrecurrent streptococcal pharyngotonsillitis recolonized with AHS compared with those receiving placebo. The recurrence rates in this study were 19% (36 of 189) and 30% (28 of 93) in patients given AHS-spray and placebo, respectively. The results of these studies suggest that use of the interference phenomena as part of the management of recurrent GABHS tonsillitis is a feasible approach that deserves further evaluation.
Effect of Antimicrobial Therapy on the Pharyngo-Tonsillar Interfering Flora An additional potential untoward outcome of penicillin therapy is the potential eradication, in the absence of BLPB, of AHS that possess inhibiting activity of GABHS.13,34,35 AHS may have a beneficial role by competing with GABHS, thus preventing colonization and subsequent infection with GABHS. However, because AHS are generally as susceptible to penicillin as is GABHS, they can also be eradicated by penicillin therapy.34 In contrast, AHS are usually more resistant to cephalosporins.35 These differ-
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Table 2 GABHS and aerobic beta-lactamase producing and interfering organisms isolated from the core of excised tonsils from 60 children33 Organism alpha-Hemolytic Streptococcus† Group A Streptococcus Staphylococcus aureus‡ Staphylococcus epidermidis‡ Moraxella catarrhalis‡ Haemophilus influenzae Type b‡ Non-type b‡ Haemophilus parainfluenzae‡ Pseudomonas aeruginosa Escherichia coli Total (all organisms)
Penicillin (n ⫽ 20)
Cefprozil (n ⫽ 20)
6 11 13 3 8
(1)* (13) (1) (7)
16 (9) 2* 2 (2)* 1 (0) 2 (2)
4 11 2 1
(2) (7) (2) (1)
1 (0) 3 (1)* 0 1 (1)
72 (33)
42 (6)*
No therapy (n ⫽ 20) 18 15 12 2 10
(8) (12) (1) (9)
3 (1) 11 (6) 2 (2) 1 (1) 103 (32)
*P ⬍ 0.01 vs other group. †Number of strains inhibiting GABHS in parenthesis. ‡Number of BLPB in parenthesis.
ences in susceptibility of cephalosporins to beta-lactamases produced by S aureus, Haemophilus influenzae, and Moraxella catarrhalis may explain the improved activity of these agents compared with penicillin in the treatment of acute pharyngo-tonsillar infections. The occurrence of these phenomena was shown in vivo using a subcutaneous abscess model in mice.35 In mice infected with GABHS and an interfering AHS (Streptococcus salivarius), penicillin eliminated both organisms. Penicillin did not, however, reduce the number of GABHS or the AHS in the presence of beta-lactamase-producing S aureus. In contrast, therapy with a second generation cephalosporin (cefprozil) eliminated GABHS and S aureus, but not the cephalosporin-resistant AHS. Beta-lactamase-producing S aureus was therefore able to protect GABHS from penicillin. However, this protection was not present after administration of the cephalosporin. Furthermore, cephalosporin therapy eradicated GABHS while preserving the AHS. A clinical study36 compared the effect on the tonsil flora of therapy with penicillin as compared with therapy with a second-generation cephalosporin (cefprozil) in 60 children scheduled for elective tonsillectomy because of recurrent GABHS tonsillitis (Table 2). For 10 days before tonsillectomy, groups of 20 patients received either penicillin, cefprozil, or no therapy. GABHS were isolated from 15 patients (75%) in the untreated group, 11 (55%) in the penicillin group, and 2 (10%) in the cefprozil groups (P ⬍ 0.001). Thirty-two BLPB isolates were recovered from 19 (95%) patients in the untreated group, 33 from 17 (85%) patients in the penicillin group, and 6 from 4 (20%) patients in the cefprozil groups (P ⬍ 0.01). AHSinhibiting GABHS were less often recovered from patients treated with penicillin. These data suggest that of the 2 antimicrobials, the cephalosporin was more effective in eradicating GABHS, reducing the number of BLPB, and preserving AHS that can
inhibit GABHS. This study also offers an explanation for the greater efficacy of cephalosporins compared with penicillin in the eradication of GABHS tonsillitis. The greater efficacy of the second-generation cephalosporin may be due to its activity against the aerobic BLPB recovered from the patients (ie, S aureus, H influenzae, and M catarrhalis) and its relative lack of activity against AHS (some of which possess interfering capability against GABHS).36
OTITIS MEDIA The nasopharynx and adenoids of healthy individuals are usually colonized by relatively nonpathogenic aerobic and anaerobic bacteria,37 some of which possess the ability to interfere with the growth of potential pathogens.13,38 These organisms include the aerobic AHS (mostly Streptococcus mitis and S sanguis)36 and anaerobic streptococci (Peptostreptococcus anaerobius) and Prevotella melaninogenica.7 Conversely, nasopharyngeal and adenoidal carriage of potential upper respiratory tract pathogens such as S pneumoniae, H influenzae, and M catarrhalis increases significantly in otitis media-prone (OMP) children and in the general population of young children during respiratory illness.39 The presence of organisms with interfering potential in the nasopharynx and adenoids may play a role in the prevention of upper respiratory tract infections.
Clinical Evidence for BI in Otitis Media In a study that determined the quantitative nasopharyngeal bacteriology of AHS and nontypeable H H influenzae in 34 OMP and 25 non-OMP children, Bernstein et al40 recovered a significantly greater number of AHS in the adenoids of non-OMP children as compared with OMP ones. In contrast, they concomitantly found a higher number of non-
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The Role of Bacterial Interference in Otitis. . .
typeable H influenzae isolates in the OMP group as compared to the non-OMP one. These findings suggest the potential protective nature of AHS in the prevention of otitis media. We compared the isolation rate of potential pathogens and aerobic and anaerobic interfering bacteria in the adenoids of 25 OMP to their isolation in 25 non-OMP children who had elective adenoedectomy (Table 1).41 Twenty-seven potential pathogens were isolated from 21 of the 25 OMP children and 10 were recovered from 8 of the 25 non-OMP children (P ⬍ 0.05). BI was noted in 71 instances against 4 potential pathogens (H influenzae, M catarrhalis, S pneumoniae, and GABHS) by 26 normal flora isolates that were recovered from the OMP group, and 193 instances by 63 isolates from the non-OMP group (P ⬍ 0.05). These interfering organisms included alpha and non-hemolytic streptococci, Prevotella spp, and Peptostreptococcus spp. These findings suggest that the adenoids of OMP children contains less aerobic and anaerobic organisms with interfering capability and more potential pathogens as compared with non-OMP children. In another study we compared the frequency of recovery of potential pathogens and aerobic and anaerobic interfering bacteria in the nasopharynx of OMP or nonOMP children (Table 1).42 Eighteen potential bacterial pathogens were isolated for 12 of the 20 OMP children and 9 were recovered from 5 of the 20 non-OMP children (P ⬍ 0.05). BI was observed in 58 instances against 4 potential pathogens by 22 normal flora isolates that were recovered from the OMP group, and in 139 by 57 isolates from the N-OMP group (P ⬍ 0.05). These interfering isolates included alpha and non-AHS, Prevotella spp, and Peptostreptococcus spp. This study shows that the nasopharyngeal flora of non-OMP children contains more aerobic and anaerobic organisms with interfering capabilities and fewer potential pathogens as compared with OMP children.
Therapeutic Use of BI in Otitis Media Roos et al43 recently reported their experience of spraying AHS with interfering activity into the nose of 130 otitisprone children (more than 6 episodes of acute otitis media within 1 year or 3 or more within 6 months). The recolonization was initiated immediately after antibiotic therapy of an acute episode of otitis media. The spray consisted of 2 Streptococcus sanguis, 2 Streptococcus mitis, and 1 Streptococcus oralis strain in equal proportions. The recolonization continued for 10 days and a “booster dose” of the spray was given 2 months later. Forty-two percent (22 of 53) of the children who received the AHS spray remained healthy during the follow-up period and had a normal tympanic membrane compared with 22% (12 of 55) in the placebogroup. Furthermore, a significantly lower number of children who were treated with active spray had secretory otitis media after 3 months of follow-up.
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Effect of Antimicrobial Therapy on BI Administration of antimicrobial agents can influence the composition of the nasopharyngeal bacterial flora.44-47 Members of the oral flora with interfering capability (eg, aerobic and anaerobic streptococci as well as penicillinsusceptible P melaninogenica strains) are generally susceptible to amoxicillin. Beta-lactamase-producing P melaninogenica strains are resistant to amoxicillin but are susceptible to amoxicillin-clavulanate. All of these members of the oral flora are relatively resistant to second- and third-generation cephalosporin therapy. Two recent studies46,47 compared the effect of 2 antimicrobial agents used to treat acute otitis media in children on the nasopharyngeal flora. Both studies compared treatment with amoxicillin-clavulanate to a second (cefprozil) and a third (cefdinir) generation cephalosporins (Fig 2). Amoxicillin-clavulanate has a wide spectrum of antimicrobial efficacy, including activity against potentially interfering organisms, whereas the cephalosporins are less potentially inhibitory toward these protective organisms. Both therapy groups exhibited similar clinical cure rates and the eradication of potential pathogens. However, the nasopharyngeal flora contained more organisms with interfering potentials after therapies with either of the cephalosporins, as compared with amoxicillin-clavulanate.46,47 Both studies showed that the oropharyngeal flora at the end of amoxicillin-clavulanate therapy was more depleted of organisms with protective potential than the oral flora after cefprozil or cefdinir therapies. However, the long-term consequences of these observations and the speed at which the oral flora regain their original balance require further study. The effect of antimicrobial therapy with amoxicillin or a second-generation cephalosporin (cefprozil) on the bacterial flora of the adenoids was studied.45 Sixty children scheduled for elective adenoidectomy because of recurrent otitis media participated in a prospective randomized study. They were randomized before surgery into 3 groups of either no therapy or 10 days of either amoxicillin or cefprozil therapy. Core adenoids materials were quantitatively cultured for aerobic and facultative bacteria. The in vitro ability of all isolates to inhibit the growth of non-type-b H influenzae and S pneumoniae was determined. The number of organisms in adenoids recovered from patients treated with either antibiotic was reduced compared with controls. However, in patients treated with amoxicillin, a significant decline in the number of AHS, and an increase (in S aureus) or no change in the number of other BLPB was noted. In contrast, in those treated with the cephalosporin, no change was noted in the frequency of recovery of AHS, and the number of BLPB decreased. Interfering AHS were more often recovered in patients treated with the cephalosporin.
SINUSITIS The origin of pathogens introduced into the sinuses that eventually cause sinusitis is nasopharyngeal and nasal flora.
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Figure 2 Effect of antimicrobial therapy on the recovery of 3 types of interfering bacteria (alpha-hemolytic streptococci, Prevotella melaninogenica, and Peptostreptococcus anaerobius) that inhibit the growth of potential pathogens (Streptococcus pneumoniae, Haemophilus influenzae, and Moraxella catarrhalis.) in children treated with either amoxicillin-clavulanate (n ⫽ 25) or cefdinir (n ⫽ 25) for acute otitis media.47 (Blue column ⫽ number of interfering isolates recovered prior to therapy, green column ⫽ number of isolates recovered after therapy. (SP, Streptococcus pneumoniae; HI, Haemophilus influenzae; MC, Moraxella catarrhali)
The normal nasal flora is made of certain bacterial species that include S aureus, Staphylococcus epidermidis, alpha and gamma streptococci, Propionibacterium acnes, and aerobic diphteroides.48-51 Potential sinus pathogens have been relatively rarely isolated from healthy nasal cavity. These included S pneumoniae (0.5% to 15%), H influenzae (0% to 6%), M catarrhalis (0% to 4%), GABHS (0% to 1%), and the anaerobic bacteria Peptostreptococcus spp (7% to 16%) and Prevotella spp (6% to 8%).41,42,48,49 In contrast to the healthy flora, the nasal cavity of patients with sinusitis is different: while the isolation of staphylococcus and diphtheroids is reduced, the recovery of pathogens increases. S pneumoniae was found in 36% of patients, H influenzae in over 50%, GABHS in 6%, and M catarrhalis in 4%.48,52,53 A recent study54 compared the frequency of recovery of potential pathogens and aerobic and anaerobic interfering bacteria in the nasopharynx and nasal cavity of 20 sinusitis prone (SP) children, to their recovery in 20 non-SP children. Twenty-one potential pathogens were isolated from nasopharyngeal cultures of 14 of the 20 SP children, and 10 from 6 of the 20 non-SP children (P ⬍ 0.05). BI was noted in 64 instances against 4 potential pathogens by 27 normal flora isolates that were recovered from the SP group, and in 144 instances by 76 isolates from the non-SP group (P ⬍ 0.05) (Table 1). Nineteen potential pathogens were recovered from nasal cultures of 13 of the 20 SP children, and 8 were isolated from 5 of the 20 non-SP (P ⬍ 0.05). BI was noted in 21 instances by 13 normal flora isolates that were recovered from the SP group, and in 63 instances by 41 isolates from the non-SP group (P ⬍ 0.05). These finding illustrate that the nasopharyngeal and nasal flora of non-SP children
contains more aerobic and anaerobic organisms with interfering capability and less potential pathogens as compared with SP children. The finding of an increase in the colonization with potential respiratory pathogens in SP as compared to non-SP children are similar to those reported in OMP and non-OMP children39,40,55-58 H influenzae, S pneumoniae, and M catarrhalis were more frequently isolated in OMP than in non-OMP patients. The presence of organisms with interfering potential may play a role in the prevention of sinusitis as well as other URTIs. Alternatively, it is possible that the prior frequent use of antibiotics in children who are SP may have reduced the number of organisms inhibitory to the growth of pathogens. It is plausible that maintenance of the normal nasopharyngeal flora that possesses inhibitory potential of pathogens can contribute to the reduction of recurrent sinus infection. This can be achieved by using narrow spectrum antibiotics that eliminate the potential pathogen(s) but spare the interfering organisms.46,47 Preliminary data illustrated the use of antibiotics with wide spectrum of efficacy against members of the oral flora may enhance colonization with potential pathogens.47
CONCLUSIONS BI may play an important role in maintaining the individual’s normal health and prevent oropharyngeal colonization or infection by potential bacterial pathogens. Understanding the mechanisms and interactions that occur in the process of
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The Role of Bacterial Interference in Otitis. . .
bacterial interference and selection of antimicrobial agents, that spare the normal flora can assist in preserving the normal interfering flora. BI can assist in the process of recovery from infection, in the promotion of health, and the prevention of upper respiratory tract infection. More research is needed to evaluate the efficacy of artificial colonization of interfering organism in the oropharyngeal mucus membranes as a method of preventing infections. This yet relatively unexplored tool may gain practical importance in an era of increases microbial resistance against antibiotics.
REFERENCES 1. Rotimi VO, Duerden BI. The development of the bacterial flora in normal neonates. J Med Microbiol 1981;14:51– 62. 2. Bibel DJ, Aly R, Bayles C, Strauss WG, et al. Competetive adherence as a mechanism of bacterial interference. Can J Microbiol 1983;29: 700 –3. 3. Wannamaker LW. Bacterial interference and competition. Scand J Infect Dis Suppl 1980;Suppl 24:82–5. 4. Smith H. The revival of interest in mechanisms of bacterial pathogenicity. Biol Rev 1995;70:277–316. 5. Dajani A, Tom M, Law DJ. Viridins, bacteriocins of alpha-hemolytic streptococci: isolation, characterization and partial purification. Antimicrob Agents Chemother 1976;9:81– 8. 6. Jack RW, Tagg JR, Ray B. Bacteriocins of gram-positive bacteria. Microbiol Rev 1995;59:171–200. 7. Daw MA, Falkiner FR. Bacteriocins: nature, function and structure. Micron. 1996;27:467–79. 8. Parker MW, Pattus F, Tucker AD, et al. Structure of the membrane pore forming fragment of the colicin A. Nature 1989;337:93– 6. 9. Jack RW, Tagg JR, Ray B. Bacteriocins of gram-positive bacteria. Microbiol Rev 1995;59:171–200. 10. Murray PR, Rosenblatt JE. Bacterial interference by oropharyngeal and clinical isolates of anaerobic bacteria. J Infect Dis 1976;134: 281–5. 11. Kaplan EL, Johnson DR. Unexplained reduced microbiological efficacy of intramuscular benzathine penicillin G and of oral penicillin V in eradication of group a streptococci from children with acute pharyngitis. Pediatrics 2001;108:1180 – 6. 12. Brook I. The role of beta-lactamase-producing bacteria in the persistence of streptococcal tonsillar infection. Rev Infect Dis 1984;6:601–7. 13. Sanders WE. Bacterial interference: I. its occurrence among the respiratory tract flora and characterization of inhibition of group A streptococci by viridans streptococci. J Infect Dis 1969;120:698 –707. 14. Crow CC, Sanders Jr, WE Longley S. Bacterial interference. II. Role of the normal throat flora in prevention of colonization by group A Streptococcus. J Infect Dis 1973;128:527–32. 15. Sanders CC, Sanders Jr, WE Harrowe DJ. Bacterial interference: effects of oral antibiotics on the normal throat flora and its ability to interfere with group A streptococci. Infect Immun 1976;13:808 –12. 16. Sanders CC, Nelson GE, Sanders WE. Bacterial interference, IV: epidemiologic determinants of the antagonistic activity of the normal throat flora against group A streptococci. Infect Immun 1977;16:599 – 603. 17. Johanson WG, Blackstock R, Pierce AK. The role of bacterial antagonism in pneumococcal colonization of the human pharynx. J Lab Clin Med 1970;75:946 –52. 18. Aly R, Maibach HI, Shinefield HR, et al. Bacterial interference among strains of Staphylococcus aureus in man. J Infect Dis 1974;129:720 – 4. 19. Roos K, Grahm E, Lind L, et al. Treatment of recurrent streptococcal tonsillitis by recolonization with alpha-streptococci. Eur J Clin Microbiol Infect Dis 1989;8:318 –9.
145 20. Dajani AS, Wannamaker LW. Experimental infection of the skin in the hamster simulating human impetigo. III. Interaction between staphylococci and group A streptococci. J Exp Med 1971;134:588 –94. 21. Dajani AS, Tom MC, Law DJ. Viridins, enteriocins of alphahemolytic streptococci: isolation, characterization, and partial purification. Antimicrob Agents Chemother 1976;9:81– 8. 22. Tagg JR, Dajani AS, Wannamaker LW, et al. Group A streptococcal bacteriocin. Production, purification, and mode of action. J Exp Med 1973;138:1168 – 83. 23. Beck A. Interference by an alpha-hemolytic streptococcus of betahemolytic pathogenic streptococci. Inflammation 1979;3:463–5. 24. Roos K, Grahn E, Holm SE. Evaluation of beta-lactamase activity and microbial interference in treatment failures of acute streptococcal tonsillitis. Scand J Infect Dis 1986;18:313–9. 25. Fujimori I, Kikushima K, Hisamatsu K, et al. Interaction between oral alpha-streptococci and group A streptococci in patients with tonsillitis. Ann Otol Rhinol Laryngol 1997;106:571– 4. 26. Grahn E, Holm SE. Bacterial interference in the throat flora during a streptococcal tonsillitis outbreak in an apartment house area. Zbl Bakt Hyg A 1983;256:72–9. 27. Brook I, Gober AE. Role of bacterial interference and beta-lactamaseproducing bacteria in the failure of penicillin to eradicate group A streptococcal pharyngotonsillitis. Arch. Otolaryngol. Head Neck Surg. 1995;121:1405–1409. 28. Brook I, Gober AE. Bacterial interference by aerobic and anaerobic bacteria in children with recurrent group A beta-hemolytic streptococcal tonsillitis. Arch Otolaryngol Head Neck Surg 1999;125:552– 4. 29. Sprunt K, Leidy G. The use of bacterial interference to prevent infection. Can J Microbiol 1988;34:332– 8. 30. Roos K, Grahn E, Holm SE, et al. Interfering alpha-streptococci as a protection against recurrent streptococcal tonsillitis in children. Int J Pediatr Ot 1993;25:141– 8. 31. Roos K, Holm SE, Grahn E, et al. Alpha-streptococci as supplementary treatment of recurrent streptococcal tonsillitis: a randomized placebo-controlled study. Scand J Infect Dis 1993;25:31–5. 32. Roos K, Holm SE, Grahn-Hakansson E, et al. Recolonization with selected alpha- streptococci for prophylaxis of recurrent streptococcal pharyngotonsillitis: a randomized placebo-controlled multicentre study. Scand J Infect Dis 1996;28:459 – 62. 33. Falck G, Grahn-Håkansson E, Holm SE, et al. Tolerance and efficacy of interfering alpha-streptococci in recurrence of streptococcal pharyngotonsillitis: a placebo-controlled study. Acta Otolaryngol (Stockh) 1999;119:944 – 8. 34. Grahn E, Holm SE, Roos K. Penicillin tolerance in beta-streptococci isolated from patients with tonsillitis. Scand J Infect Dis 1987;19: 421– 6. 35. Brook I, Gillmore JD. Evaluation of bacterial interference and betalactamase production in the management of experimental infection with group A beta-hemolytic streptococci. Antimicrob Agents Chemother 1993;37:1452–5. 36. Brook I, Foote PA. Effect of penicillin or cefprozil therapy on tonsillar flora. J. Antimicrob Chemother 1997;40:725– 8. 37. Mackowiak PA. The normal flora. N Engl J Med 1983;307:83–93. 38. Sprunt K, Redman W. Evidence suggesting importance of role of interbacterial inhibition in maintaining balance of normal flora. Ann Intern Med 1968;68:579 –90. 39. Faden H, Zaz MJ, Bernstein JM, et al. Nasopharyngeal flora in the first three years of life in normal and otitis-prone children. Ann Otolo Rhinolo Laryngolo 1991;100:612–5. 40. Bernstein JM, Sagahtaheri-Altaie S, Dryjd DM, et al. Bacterial interference in nasopharyngeal bacterial flora of otitis-prone and nonototis-prone children. Acta oto- rhino-laryngologica belgium 1994;48: 1–9. 41. Brook I, Yocum P. Bacterial interference in the adenoids of otitis media prone children. Ped Infect Dis J 1999;18:835–7. 42. Brook I, Gober A. Bacterial interference in the nasopharynx of otitis media prone and not otitis media prone children. Arch Otolaryngol Head Neck Surg 2000;126:1011–3.
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43. Roos K, Grahn Håkansson E, Holm S. Effect of recolonisation with “interfering” alpha- streptococci on recurrences of acute and secretory otitis media in children: randomised placebo controlled trial. BMJ 2001;322:210 –2. 44. Foote Jr, PA Brook I. Penicillin and clindamycin therapy in recurrent tonsillitis. Effect of microbial flora. Arch Otolaryngolo Head Neck Surg 1989;15:856 –9. 45. Brook I, Foote PA. Bacterial interference and beta-lactamase-producing bacteria in the adenoids after antimicrobial therapy. Rev Inf Dis 1997;25:493. 46. Brook I, Gober AE. Bacterial interference in the nasopharynx following antimicrobial therapy of acute otitis media. J Antimicrob Chemother 1998;41:489 –92. 47. Brook I, Gober AE. Long-term effects on the nasopharyngeal flora of children following antimicrobial therapy of acute otitis media with cefdinir or amoxycillin-clavulanate. J Med Microb (In press). 48. Jousimies-Somer HR, Savolainen S, Ylikoski JS. Comparison of the nasal bacterial floras in two groups of healthy subjects and in patients with acute maxillary sinusitis. Clin Microbiol 1989;27:2736 – 43. 49. Brook I. Aerobic and anaerobic bacteriology of purulent nasopharyngitis in children. J Clin Microbiol 1988;26:592– 4. 50. Savolainen S, Ylikoski J, Jousimies-Somer H. The bacterial flora of the nasal cavity in healthy young men. Rhinology 1986;24:249 –55.
51. Winther B, Brofeldt S, Gronborg H, et al. Study of bacteria in the nasal cavity and nasopharynx during naturally acquired common colds. Acta Otolaryngol (Stockh) 1984;98:315–20. 52. Gwaltney JM Jr, Sydnor A Jr, Sande MA. Etiology and antimicrobial treatment of acute sinusitis. Ann Otol Rhinol Laryngol 1981;Suppl; 90(3 Pt 3):68-71. 53. Nylen O, Jeppsson PH, Branefors-Helander P. Acute sinusitis: a clinical bacteriological and serological study with special reference to Haemophilus influenzae. Scand J Infect Dis 1972;4:43– 8. 54. Brook I, Gober A. Bacterial interference in the nasopharynx and nasal cavity of sinusitis prone and not sinusitis prone children. Acta Otolaryngol 1999;119:832– 6. 55. Faden H, Zaz MJ, Bernstein JM, et al. Nasopharyngeal flora in the first three years of life in normal and otitis-prone children. Ann Otol Rhin Laryngol 1991;100:612–5. 56. Stenfors LE, Raisanen S. The flora of the nasopharynx, with special reference to middle ear pathogens. Acta Otolaryngol (Stockh) 1989; 108:122–5. 57. Faden H, Harabuchi Y, Hong JJ. Epidemiology of moraxella catarrhalis in children during the first 2 years of life: relationship to otitis media. J Infect Dis 1994;169:1312–7. 58. Fujimori I, Hisamatsu K, Kikushima K, et al. The nasopharyngeal bacterial flora in children with otitis media with effusion. Eur Arch Otolaryngol 1996;253:260 –3.
REVIEW
The Role of Bacterial Interference in Otitis, Sinusitis and Tonsillitis Itzhak Brook, MD, MSc From the Department of Pediatrics, Georgetown University. Bacterial interactions that include antagonism (interference) and synergism help maintain balance between the members of the normal endogenous flora. Alpha-streptococci that predominate in the normal respiratory tract flora attracted most attention in studies of bacterial interference. Other organisms that possess interfering characteristics in upper respiratory tract infections (URTIs) are nonhemolytic streptococci, and Prevotella and Peptostreptococcus spp. The production of bacteriocins by some microorganisms is one of the important mechanisms of interference. The role of bacterial interference in the development of URTI and its effect on the eradication of these infections is discussed. These infections include pharyngo-tonsillitis, otitis media, and sinusitis. Treatment with various antimicrobial agents can affect the balance between members of the oro-pharyngeal bacterial flora and interfering organisms. Implantation into the indigenous microflora of low virulence bacterial strains that are potentially capable of interfering with colonization and infection with other more virulent organisms has been used in preliminary studies as a means of coping with the failure of antimicrobials in the treatment of several URTI. © 2005 American Academy of Otolaryngology–Head and Neck Surgery Foundation, Inc. All rights reserved.
Bacterial colonization of the mucous membranes is initiated in the newborn immediately after delivery.1 The process of colonization of mucus membranes evolves competitive interactions between the various micro-organisms. Bacteria interactions occur when micro-organisms compete to establish themselves and dominate their environment. Some of these interactions are synergistic while others are antagonistic, as organisms can interfere with each other’s growth and compete for their ecological space. Bacterial interference (BI) can have a major role in maintaining the normal flora of skin and mucous membranes by preventing Reprint request: Itzhak Brook, MD, MSc, 4431 Albemarle St, NW, Washington DC 20016.
colonization and subsequent invasion by potential pathogenic bacteria (Fig 1). This phenomenon is most important in preventing certain bacterial infections. Several mechanisms account for BI. One proposed mechanism is that the normal bacteria occupy certain sites on the epithelial surface cells and thus prevent pathogens from adhering to these cells.2 Other mechanisms includes changes in the bacterial microenvironment, the production of antagonistic substances by some bacteria, and competition for needed nutritional substances.3,4 The mediators of BI include bacteriophages and the production of complex materials by micro-organisms such as bacteriocins or bacteriolytic enzymes and less complex molecules such as hydrogen peroxide, lactic, or fatty acids and ammonia.3,4 Bacteriocins are bactericidal proteins that are generated by bacteria and are extracellular toxins that selectively kill other bacteria and promote colonization.5 Unlike traditional antibiotics, some have a broad spectrum while others possess narrow spectrum of activity and only kill bacteria of the same or closely related species.6,7 The strains producing a bacteriocin are generally resistant to the bacteriocins they produce. The mode of action of bacteriocins with larger molecules is through adsorption to their specific outer membrane receptor that is present on the susceptible cells. They are thereafter translocated to their specific target(s) within these cells.8 This is followed by significant biologic and morphologic changes in the targeted bacterial cell and probably also in the bacteriocin particle. The recent worldwide emergence of increasing resistance to antimicrobial agents has generated interest in BI as a means of controlling the problem. This approach evolves substituting the use of antimicrobial therapy with artificial E-mail address: [email protected].
0194-5998/$30.00 © 2005 American Academy of Otolaryngology–Head and Neck Surgery Foundation, Inc. All rights reserved. doi:10.1016/j.otohns.2005.03.012
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Figure 1 Role of normal flora in preventing colonization and subsequent infection by pathogenic bacteria.
implantation into the indigenous microflora bacterial strains of low virulence that are potentially capable of interfering with colonization and subsequent infection with more virulent organism(s). Antibiotic therapy can also affect the balance between pathogens and normal flora by disrupting the ecological balance thus facilitating recurrent upper respiratory tract infections (URTI). Alpha-streptococci (AHS) that predominate in the normal respiratory tract flora have attracted the most attention in studies of bacterial interference.9 Most AHS can produce bacteriocins.7,8 Other organisms that possess interfering characteristics in URTI are non-hemolytic streptococci, and Prevotella and Peptostreptococcus spp.10 This review is focused on the role of BI in the development, prevention and eradication of URTI.
STREPTOCOCCAL PHARYNGOTONSILLITIS The failure of penicillin therapy to eradicate tonsillitis caused by Group A beta hemolytic streptococci (GABHS) is of great clinical concern. In a recent study,11 more than 35% patients treated with oral penicillin V and 37% of benzathine penicillin G-treated patients were microbiologic treatment failures at either 10 to 14 or 29 to 31 days after therapy. Various theories have been offered to explain this phenomenon. One is that beta-lactamase-producing bacteria (BLPB) can “shield” GABHS by inactivating penicillin. BLPB were recovered from over 75% of the tonsils of patients who had tonsillectomy for recurrent infection.12 Another explanation is that interfering organisms such as AHS that are part of the normal oral flora are missing in many of those patients who fail penicillin therapy.13-16 These AHS play an important protective role in preventing colonization and subsequent infection by GABHS and their absence may lead to failure of penicillin therapy.13
Clinical Evidence for BI The interactions between GABHS and other bacteria in the oropharynx have been studied over the past 30 years. Crow et al14 demonstrated that children who subsequently became colonized with GABHS were less often colonized by flora inhibitory or bactericidal for GABHS than those who did not become colonized with these organisms. Sanders et al15
showed that oral therapy with penicillin (and to a less extent with tetracycline) induced a decline in the number of interfering organisms, a decrease that lasted for at least 21 days after therapy. Sanders et al16 found that interfering bacteria are more often isolated during the months with the highest prevalence of GABHS infection and that the prevalence of bactericidal organisms increased with age, probably contributing to the resistance of older individuals to streptococcal infections when compared with children. The organisms with the greatest inhibitory capacity were AHS, non-hemolytic streptococci, and Neisseriae species. AHS can inhibit the colonization of a variety of pathogens such as Streptococcus pneumoniae, GABHS, and Staphylococcus aureus in patients as well as in vitro. Their production of bacteriocin and other inhibitory substances may explain this phenomenon.13,14,17,18 Suppression of some bacterial growth may also occur through utilization of nutrients in the nasopharyngeal environment essential for the colonization by potential pathogens.19 Dajani and Wannamaker20 found that many strains of AHS could produce bacteriocin. These inhibitory substances have been called viridins and one of these (viridin B) has been partially purified and characterized.21 This bacteriocin (and apparently other viridins as well) is inhibitory against Gram-positive as well as Gram-negative bacteria. GABHS also harbors an inhibitory capability through the production of peroxide as well as a bacteriocin, designated Streptocin A or streptococcin A-FF22.22 Beck23 observed a high interfering capability of a Streptococcus viridans strain isolated from an individual who was resistant to acquisition of infection with GABHS. This strain inhibited completely 72% and partially 28% of the GABHS tested. Beck suggested the “implantation” of this strain to patients with recurrent infections of GABHS as a method of preventing recurrences. The tonsils of patients with recurrent streptococcal pharyngotonsillitis harbor less AHS with interfering activity against GABHS compared with healthy individuals.24,25 Grahn and Holm26 found an increased resistance toward recurrent GABHS throat infections in family members with high numbers of interfering AHS in the throat flora as compared with those who lacked such AHS. Roos et al19,24 found that patients with recurrent GABHS pharyngotonsillitis lacked interfering AHS more often than healthy relatives who were carriers of the same type of GABHS. Roos et al24 and Brook and Gober27 showed that both production of beta-lactamase by the normal oropharyngeal flora and the lack of colonization of the pharynx by inhibiting AHS were associated with the failure of penicillin to cure GABHS tonsillitis. The role of aerobic and anaerobic organisms other than AHS in interfering with GABHS growth, was evaluated in a study by Brook and Gober.28 The authors compared the frequency of recovery of aerobic and anaerobic bacteria with interfering capability for GABHS from the tonsils of
Brook
The Role of Bacterial Interference in Otitis. . .
141
Table 1 Recovery of organisms with bacterial interference capabilities in children who are prone to infection and not prone to infection. Number of interfering organisms/individuals (average per individual) Infection type
Site cultured
Otitis media
Adenoids Nasopharynx Nasopharynx Nasal cavity Tonsils
Sinusitis Tonsillitis
Prone to infection 26/25 22/20 27/20 13/20 11/20
(1.04) (1.1) (1.35) (0.65) (0.55)
20 children with and 20 without the history of recurrent GABHS pharyngo-tonsillitis (Table 1). Eleven aerobic and anaerobic isolates with interfering capability for GABHS were recovered from 6 (30%) of the 20 children with recurrent GABHS, and 40 such organisms were isolated from 17 (85%) of the 20 without recurrences (P ⬍ 0.01). The interfering organisms included aerobic (alpha and non-hemolytic streptococci), and anaerobic organisms (Prevotella and Peptostreptococcus spp) The study illustrates that the tonsils of children with the history of recurrent GABHS infection contain less aerobic and anaerobic bacteria with interfering capability of GABHS than those without that history. It also suggests that the presence of these interfering bacteria may play a role in preventing GABHS infection.
Therapeutic Use of BI in Tonsillitis The first attempts to recolonize the throat with bacteria isolated from the normal flora to avoid overgrowth of pathogenic bacteria have been presented by Sprunt and Leidy.29 A series of 4 studies from Göteborg, Sweden30-32 evaluated the use of inoculation of the nasopharynx with interfering AHS, in the prevention of recurrent GABHS pharyngotonsillitis. This approach was used because patients treated with antibiotics often have a disrupted pharyngeal flora and may lack AHS that possess interfering activity against GABHS. The first study was open and nonrandomized and included 31 patients with recurrent streptococcal tonsillitis that were given antibiotics for 10 days.30 At the end of therapy, the patients mouths were sprayed with 4 selected AHS strains known to have strong in vitro growth inhibiting activity against most GABHS. After AHS treatment, none of the patients contracted a new episode of tonsillitis during the follow-up period of 3 months; 8% of a group of patients who did not receive AHS had a second tonsillitis. The second study was double-blind, randomized, and placebo-controlled.31 Thirty-six patients with recurrent GABHS tonsillitis were treated with antibiotics followed by mouth spraying with either placebo (19 patients) or a pool of 4 selected AHS interfering strains (17 patients). None of the patients in the AHS-treated group experienced a recur-
Not prone to infection 63/25 57/20 76/20 41/20 40/20
(2.52) (2.85) (3.8) (2.05) (2.0)
Reference number 41 41 54 54 28
rence during the first 2 months of follow-up, but 7 in those treated with antibiotics and placebo did (P ⬍ 0.05). After 3 months, only 1 patient in the group treated with AHS and 11 in the placebo-treated group had a recurrence. The third study32 was a randomized, placebo-controlled, double-blind, multi-center one. A total of 130 patients with recurrence of GABHS and clinical signs of pharyngotonsillitis were enrolled. The patients received antibiotics for 10 days, followed by 10 days of AHS-inhibitory to GABHS or placebo spray therapy. The clinical recurrences (bacteriologically verified) in the AHS- (n ⫽ 51) and placebo-treated (n ⫽ 61) patient groups were 2% (n ⫽ 1) and 23% (n ⫽ 4) respectively, in patients given spray (P ⫽ 0.004). The inclusion of “early treatment failures” reduces this difference (P ⫽ 0.064). The authors concluded that AHS given as a spray and used for at least 5 days significantly prevented recurrence of GABHS pharyngotonsillitis. The fourth study33 was randomized and placebo-controlled and included 342 patients with tonsillitis but did not focus on individuals with recurrent episodes of infection. A significantly lower number of recurrences was also found in patients with nonrecurrent streptococcal pharyngotonsillitis recolonized with AHS compared with those receiving placebo. The recurrence rates in this study were 19% (36 of 189) and 30% (28 of 93) in patients given AHS-spray and placebo, respectively. The results of these studies suggest that use of the interference phenomena as part of the management of recurrent GABHS tonsillitis is a feasible approach that deserves further evaluation.
Effect of Antimicrobial Therapy on the Pharyngo-Tonsillar Interfering Flora An additional potential untoward outcome of penicillin therapy is the potential eradication, in the absence of BLPB, of AHS that possess inhibiting activity of GABHS.13,34,35 AHS may have a beneficial role by competing with GABHS, thus preventing colonization and subsequent infection with GABHS. However, because AHS are generally as susceptible to penicillin as is GABHS, they can also be eradicated by penicillin therapy.34 In contrast, AHS are usually more resistant to cephalosporins.35 These differ-
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Table 2 GABHS and aerobic beta-lactamase producing and interfering organisms isolated from the core of excised tonsils from 60 children33 Organism alpha-Hemolytic Streptococcus† Group A Streptococcus Staphylococcus aureus‡ Staphylococcus epidermidis‡ Moraxella catarrhalis‡ Haemophilus influenzae Type b‡ Non-type b‡ Haemophilus parainfluenzae‡ Pseudomonas aeruginosa Escherichia coli Total (all organisms)
Penicillin (n ⫽ 20)
Cefprozil (n ⫽ 20)
6 11 13 3 8
(1)* (13) (1) (7)
16 (9) 2* 2 (2)* 1 (0) 2 (2)
4 11 2 1
(2) (7) (2) (1)
1 (0) 3 (1)* 0 1 (1)
72 (33)
42 (6)*
No therapy (n ⫽ 20) 18 15 12 2 10
(8) (12) (1) (9)
3 (1) 11 (6) 2 (2) 1 (1) 103 (32)
*P ⬍ 0.01 vs other group. †Number of strains inhibiting GABHS in parenthesis. ‡Number of BLPB in parenthesis.
ences in susceptibility of cephalosporins to beta-lactamases produced by S aureus, Haemophilus influenzae, and Moraxella catarrhalis may explain the improved activity of these agents compared with penicillin in the treatment of acute pharyngo-tonsillar infections. The occurrence of these phenomena was shown in vivo using a subcutaneous abscess model in mice.35 In mice infected with GABHS and an interfering AHS (Streptococcus salivarius), penicillin eliminated both organisms. Penicillin did not, however, reduce the number of GABHS or the AHS in the presence of beta-lactamase-producing S aureus. In contrast, therapy with a second generation cephalosporin (cefprozil) eliminated GABHS and S aureus, but not the cephalosporin-resistant AHS. Beta-lactamase-producing S aureus was therefore able to protect GABHS from penicillin. However, this protection was not present after administration of the cephalosporin. Furthermore, cephalosporin therapy eradicated GABHS while preserving the AHS. A clinical study36 compared the effect on the tonsil flora of therapy with penicillin as compared with therapy with a second-generation cephalosporin (cefprozil) in 60 children scheduled for elective tonsillectomy because of recurrent GABHS tonsillitis (Table 2). For 10 days before tonsillectomy, groups of 20 patients received either penicillin, cefprozil, or no therapy. GABHS were isolated from 15 patients (75%) in the untreated group, 11 (55%) in the penicillin group, and 2 (10%) in the cefprozil groups (P ⬍ 0.001). Thirty-two BLPB isolates were recovered from 19 (95%) patients in the untreated group, 33 from 17 (85%) patients in the penicillin group, and 6 from 4 (20%) patients in the cefprozil groups (P ⬍ 0.01). AHSinhibiting GABHS were less often recovered from patients treated with penicillin. These data suggest that of the 2 antimicrobials, the cephalosporin was more effective in eradicating GABHS, reducing the number of BLPB, and preserving AHS that can
inhibit GABHS. This study also offers an explanation for the greater efficacy of cephalosporins compared with penicillin in the eradication of GABHS tonsillitis. The greater efficacy of the second-generation cephalosporin may be due to its activity against the aerobic BLPB recovered from the patients (ie, S aureus, H influenzae, and M catarrhalis) and its relative lack of activity against AHS (some of which possess interfering capability against GABHS).36
OTITIS MEDIA The nasopharynx and adenoids of healthy individuals are usually colonized by relatively nonpathogenic aerobic and anaerobic bacteria,37 some of which possess the ability to interfere with the growth of potential pathogens.13,38 These organisms include the aerobic AHS (mostly Streptococcus mitis and S sanguis)36 and anaerobic streptococci (Peptostreptococcus anaerobius) and Prevotella melaninogenica.7 Conversely, nasopharyngeal and adenoidal carriage of potential upper respiratory tract pathogens such as S pneumoniae, H influenzae, and M catarrhalis increases significantly in otitis media-prone (OMP) children and in the general population of young children during respiratory illness.39 The presence of organisms with interfering potential in the nasopharynx and adenoids may play a role in the prevention of upper respiratory tract infections.
Clinical Evidence for BI in Otitis Media In a study that determined the quantitative nasopharyngeal bacteriology of AHS and nontypeable H H influenzae in 34 OMP and 25 non-OMP children, Bernstein et al40 recovered a significantly greater number of AHS in the adenoids of non-OMP children as compared with OMP ones. In contrast, they concomitantly found a higher number of non-
Brook
The Role of Bacterial Interference in Otitis. . .
typeable H influenzae isolates in the OMP group as compared to the non-OMP one. These findings suggest the potential protective nature of AHS in the prevention of otitis media. We compared the isolation rate of potential pathogens and aerobic and anaerobic interfering bacteria in the adenoids of 25 OMP to their isolation in 25 non-OMP children who had elective adenoedectomy (Table 1).41 Twenty-seven potential pathogens were isolated from 21 of the 25 OMP children and 10 were recovered from 8 of the 25 non-OMP children (P ⬍ 0.05). BI was noted in 71 instances against 4 potential pathogens (H influenzae, M catarrhalis, S pneumoniae, and GABHS) by 26 normal flora isolates that were recovered from the OMP group, and 193 instances by 63 isolates from the non-OMP group (P ⬍ 0.05). These interfering organisms included alpha and non-hemolytic streptococci, Prevotella spp, and Peptostreptococcus spp. These findings suggest that the adenoids of OMP children contains less aerobic and anaerobic organisms with interfering capability and more potential pathogens as compared with non-OMP children. In another study we compared the frequency of recovery of potential pathogens and aerobic and anaerobic interfering bacteria in the nasopharynx of OMP or nonOMP children (Table 1).42 Eighteen potential bacterial pathogens were isolated for 12 of the 20 OMP children and 9 were recovered from 5 of the 20 non-OMP children (P ⬍ 0.05). BI was observed in 58 instances against 4 potential pathogens by 22 normal flora isolates that were recovered from the OMP group, and in 139 by 57 isolates from the N-OMP group (P ⬍ 0.05). These interfering isolates included alpha and non-AHS, Prevotella spp, and Peptostreptococcus spp. This study shows that the nasopharyngeal flora of non-OMP children contains more aerobic and anaerobic organisms with interfering capabilities and fewer potential pathogens as compared with OMP children.
Therapeutic Use of BI in Otitis Media Roos et al43 recently reported their experience of spraying AHS with interfering activity into the nose of 130 otitisprone children (more than 6 episodes of acute otitis media within 1 year or 3 or more within 6 months). The recolonization was initiated immediately after antibiotic therapy of an acute episode of otitis media. The spray consisted of 2 Streptococcus sanguis, 2 Streptococcus mitis, and 1 Streptococcus oralis strain in equal proportions. The recolonization continued for 10 days and a “booster dose” of the spray was given 2 months later. Forty-two percent (22 of 53) of the children who received the AHS spray remained healthy during the follow-up period and had a normal tympanic membrane compared with 22% (12 of 55) in the placebogroup. Furthermore, a significantly lower number of children who were treated with active spray had secretory otitis media after 3 months of follow-up.
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Effect of Antimicrobial Therapy on BI Administration of antimicrobial agents can influence the composition of the nasopharyngeal bacterial flora.44-47 Members of the oral flora with interfering capability (eg, aerobic and anaerobic streptococci as well as penicillinsusceptible P melaninogenica strains) are generally susceptible to amoxicillin. Beta-lactamase-producing P melaninogenica strains are resistant to amoxicillin but are susceptible to amoxicillin-clavulanate. All of these members of the oral flora are relatively resistant to second- and third-generation cephalosporin therapy. Two recent studies46,47 compared the effect of 2 antimicrobial agents used to treat acute otitis media in children on the nasopharyngeal flora. Both studies compared treatment with amoxicillin-clavulanate to a second (cefprozil) and a third (cefdinir) generation cephalosporins (Fig 2). Amoxicillin-clavulanate has a wide spectrum of antimicrobial efficacy, including activity against potentially interfering organisms, whereas the cephalosporins are less potentially inhibitory toward these protective organisms. Both therapy groups exhibited similar clinical cure rates and the eradication of potential pathogens. However, the nasopharyngeal flora contained more organisms with interfering potentials after therapies with either of the cephalosporins, as compared with amoxicillin-clavulanate.46,47 Both studies showed that the oropharyngeal flora at the end of amoxicillin-clavulanate therapy was more depleted of organisms with protective potential than the oral flora after cefprozil or cefdinir therapies. However, the long-term consequences of these observations and the speed at which the oral flora regain their original balance require further study. The effect of antimicrobial therapy with amoxicillin or a second-generation cephalosporin (cefprozil) on the bacterial flora of the adenoids was studied.45 Sixty children scheduled for elective adenoidectomy because of recurrent otitis media participated in a prospective randomized study. They were randomized before surgery into 3 groups of either no therapy or 10 days of either amoxicillin or cefprozil therapy. Core adenoids materials were quantitatively cultured for aerobic and facultative bacteria. The in vitro ability of all isolates to inhibit the growth of non-type-b H influenzae and S pneumoniae was determined. The number of organisms in adenoids recovered from patients treated with either antibiotic was reduced compared with controls. However, in patients treated with amoxicillin, a significant decline in the number of AHS, and an increase (in S aureus) or no change in the number of other BLPB was noted. In contrast, in those treated with the cephalosporin, no change was noted in the frequency of recovery of AHS, and the number of BLPB decreased. Interfering AHS were more often recovered in patients treated with the cephalosporin.
SINUSITIS The origin of pathogens introduced into the sinuses that eventually cause sinusitis is nasopharyngeal and nasal flora.
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Figure 2 Effect of antimicrobial therapy on the recovery of 3 types of interfering bacteria (alpha-hemolytic streptococci, Prevotella melaninogenica, and Peptostreptococcus anaerobius) that inhibit the growth of potential pathogens (Streptococcus pneumoniae, Haemophilus influenzae, and Moraxella catarrhalis.) in children treated with either amoxicillin-clavulanate (n ⫽ 25) or cefdinir (n ⫽ 25) for acute otitis media.47 (Blue column ⫽ number of interfering isolates recovered prior to therapy, green column ⫽ number of isolates recovered after therapy. (SP, Streptococcus pneumoniae; HI, Haemophilus influenzae; MC, Moraxella catarrhali)
The normal nasal flora is made of certain bacterial species that include S aureus, Staphylococcus epidermidis, alpha and gamma streptococci, Propionibacterium acnes, and aerobic diphteroides.48-51 Potential sinus pathogens have been relatively rarely isolated from healthy nasal cavity. These included S pneumoniae (0.5% to 15%), H influenzae (0% to 6%), M catarrhalis (0% to 4%), GABHS (0% to 1%), and the anaerobic bacteria Peptostreptococcus spp (7% to 16%) and Prevotella spp (6% to 8%).41,42,48,49 In contrast to the healthy flora, the nasal cavity of patients with sinusitis is different: while the isolation of staphylococcus and diphtheroids is reduced, the recovery of pathogens increases. S pneumoniae was found in 36% of patients, H influenzae in over 50%, GABHS in 6%, and M catarrhalis in 4%.48,52,53 A recent study54 compared the frequency of recovery of potential pathogens and aerobic and anaerobic interfering bacteria in the nasopharynx and nasal cavity of 20 sinusitis prone (SP) children, to their recovery in 20 non-SP children. Twenty-one potential pathogens were isolated from nasopharyngeal cultures of 14 of the 20 SP children, and 10 from 6 of the 20 non-SP children (P ⬍ 0.05). BI was noted in 64 instances against 4 potential pathogens by 27 normal flora isolates that were recovered from the SP group, and in 144 instances by 76 isolates from the non-SP group (P ⬍ 0.05) (Table 1). Nineteen potential pathogens were recovered from nasal cultures of 13 of the 20 SP children, and 8 were isolated from 5 of the 20 non-SP (P ⬍ 0.05). BI was noted in 21 instances by 13 normal flora isolates that were recovered from the SP group, and in 63 instances by 41 isolates from the non-SP group (P ⬍ 0.05). These finding illustrate that the nasopharyngeal and nasal flora of non-SP children
contains more aerobic and anaerobic organisms with interfering capability and less potential pathogens as compared with SP children. The finding of an increase in the colonization with potential respiratory pathogens in SP as compared to non-SP children are similar to those reported in OMP and non-OMP children39,40,55-58 H influenzae, S pneumoniae, and M catarrhalis were more frequently isolated in OMP than in non-OMP patients. The presence of organisms with interfering potential may play a role in the prevention of sinusitis as well as other URTIs. Alternatively, it is possible that the prior frequent use of antibiotics in children who are SP may have reduced the number of organisms inhibitory to the growth of pathogens. It is plausible that maintenance of the normal nasopharyngeal flora that possesses inhibitory potential of pathogens can contribute to the reduction of recurrent sinus infection. This can be achieved by using narrow spectrum antibiotics that eliminate the potential pathogen(s) but spare the interfering organisms.46,47 Preliminary data illustrated the use of antibiotics with wide spectrum of efficacy against members of the oral flora may enhance colonization with potential pathogens.47
CONCLUSIONS BI may play an important role in maintaining the individual’s normal health and prevent oropharyngeal colonization or infection by potential bacterial pathogens. Understanding the mechanisms and interactions that occur in the process of
Brook
The Role of Bacterial Interference in Otitis. . .
bacterial interference and selection of antimicrobial agents, that spare the normal flora can assist in preserving the normal interfering flora. BI can assist in the process of recovery from infection, in the promotion of health, and the prevention of upper respiratory tract infection. More research is needed to evaluate the efficacy of artificial colonization of interfering organism in the oropharyngeal mucus membranes as a method of preventing infections. This yet relatively unexplored tool may gain practical importance in an era of increases microbial resistance against antibiotics.
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43. Roos K, Grahn Håkansson E, Holm S. Effect of recolonisation with “interfering” alpha- streptococci on recurrences of acute and secretory otitis media in children: randomised placebo controlled trial. BMJ 2001;322:210 –2. 44. Foote Jr, PA Brook I. Penicillin and clindamycin therapy in recurrent tonsillitis. Effect of microbial flora. Arch Otolaryngolo Head Neck Surg 1989;15:856 –9. 45. Brook I, Foote PA. Bacterial interference and beta-lactamase-producing bacteria in the adenoids after antimicrobial therapy. Rev Inf Dis 1997;25:493. 46. Brook I, Gober AE. Bacterial interference in the nasopharynx following antimicrobial therapy of acute otitis media. J Antimicrob Chemother 1998;41:489 –92. 47. Brook I, Gober AE. Long-term effects on the nasopharyngeal flora of children following antimicrobial therapy of acute otitis media with cefdinir or amoxycillin-clavulanate. J Med Microb (In press). 48. Jousimies-Somer HR, Savolainen S, Ylikoski JS. Comparison of the nasal bacterial floras in two groups of healthy subjects and in patients with acute maxillary sinusitis. Clin Microbiol 1989;27:2736 – 43. 49. Brook I. Aerobic and anaerobic bacteriology of purulent nasopharyngitis in children. J Clin Microbiol 1988;26:592– 4. 50. Savolainen S, Ylikoski J, Jousimies-Somer H. The bacterial flora of the nasal cavity in healthy young men. Rhinology 1986;24:249 –55.
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