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In vitro activity of lomefloxacin and other antimicrobials against bacterial enteritis pathogens
DIAGN MICROBIOLINFECT DIS 1992;15:339-343
339
In vitro Activity of Lomefloxacin and Other Antimicrobials Against Bacterial Enteritis Pathogens David Felmingham and Marion J. Robbins
Lomefloxacin is a new, difluoroquinolone. In this study, the in vitro activity of lomefloxacin against clinical isolates of a variety of bacterial species associated with acute diarrheal disease was determined and compared with that of ciprofloxacin, ofloxacin, amoxicillin, sulphamethoxazole, trimethoprim, tetracycline, and chloramphenicol. Bacterial isolates were obtained from different geographical areas, including Western Europe and the United Kingdom, Southern Europe, Africa, the Middle East, South and Southeast Asia, and South America, and were included to reflect the range of susceptibility seen throughout the world. Minimum inhibitory concentrations (MICs) were determined using an agar incorporation technique in Mueller-Hinton medium supplemented when neces-
sary with saponin-lysed horse blood at a final concentration of 10% vol/vol. Lomefloxacin was highly active against all the species examined which included Salmonella spp., Shigella spp., Escherichia coli enterotoxigenic [(ETEC), enteroinvasive (EIEC), and enteropathogenic (EPEC) strains], Yersinia enterocolitica, Campylobacter jejuni, Vibrio spp., and Aeromonas hydrophila, with all isolates inhibited by 1 mg/L or less. This activity was similar to ofloxacin and slightly less than that of ciprofloxacin. By contrast, many of the isolates were resistant to one or more of the other, unrelated animicrobials. No cross-resistance between lomefloxacin and any of the nonfluoroquinolone antimicrobials examined in the study was observed.
INTRODUCTION
In a previous study of the susceptibility of a variety of bacterial enteropathogens to 10 antimicrobials, including ampicillin, cotrimoxazole, and doxycycline, Carlson et al. (1983) concluded that the most active agents of those examined were the two fluoroquinolones, enoxacin and norfloxacin. More recently, Felmingham et al. (1985), in a study of the activity of twelve 4-quinolones against bacterial enteric pathogens, showed that all of the new fluoroquinolones, including enoxacin and norfloxacin, were highly active with ofloxacin and ciprofloxacin possessing the greatest potency. In this study, we have determined the in vitro activity of lomefloxacin (1-ethyl-6,8-difluoro-l,4dihydro7-(3-methyl-l-piperazinyl)-4-oxo quinoline3-carboxylic acid monohydrochloride), a new difluoroquinolone with a broad and potent spectrum of antibacterial activity (Robbins et al., 1989), against a variety of bacterial species associated with acute diarrheal disease and compared it with that of amoxicillin, sulphamethoxazole, trimethoprim, tetracycline, and chloramphenicol.
Acute diarrheal disease, caused by bacterial, viral, or parasitic infection, is a worldwide problem. However, the greatest morbidity and mortality is seen in the developing countries of Africa, the Middle East, South and Southeast Asia, and South America, where the infections are most frequently of bacterial etiology. The bacterial species associated with acute infectious diarrhea include Escherichia coli [Enterotoxigenic (ETEC), enteroinvasive (EIEC), and enteropathogenic (EPEC) strains], Salmonella spp., Shigella spp., Yersinia enterocolitica, Campylobacter jejuni, Vibrio cholerae, V ibrio parahaemolyticus , and Aeromonas hydrophila.
From the Department of Clinical Microbiology,University of College Hospital, London, England. Address reprint requests to D. Felmingham, Department of Clinical Microbiology,University College Hospital, Grafton Way, London WCIE 6AU, England, UK. Received 2 April 1991, revised and accepted 1 July 1991. © 1992Elsevier Science Publishing Co., Inc. 655 Avenue of the Americas, New York, NY 10010 0732-8893/92/$5. O0
340
D. Felmingham and M.J. Robbins
MATERIALS A N D M E T H O D S Bacterial Isolates Bacterial isolates used in this study were derived from clinical material examined in the Department of Clinical Microbiology at University College Hospital, London, supplemented with strains from Southern Europe, Africa, the Middle East, South and Southeast Asia, and South America kindly supplied by colleagues at the Hospital for Tropical Diseases, London and the London School of Hygiene and Tropical Medicine. The collection of bacteria studied was designed to reflect the range of antimicrobial susceptibility seen throughout the world and not to represent that seen in defined epidemiological populations.
with saponin-lysed horse blood (Tissue Culture Services) to a final concentration of 10% volYvol. The inoculum used was approximately 104 colony forming units (CFU) of each isolate, contained in 1 p~l. Following inoculation, plates were incubated in air at 37°C for 18-24 hr except those inoculated with the isolates of Campylobacter jejuni, which were incubated microaerophilically (BBL Camypak System) at 37°C for 48 hr. MICs were determined as the lowest concentration of antimicrobial tested that completely inhibited macroscopically visible surface growth of the inoculum after reference to an antimicrobial-free control plate. Escherichia coli (NCTC 10418) and Staphylococcus aureus (NCTC 6571) were included throughout as control bacterial strains.
Antimicrobials RESULTS Substances of known potency were obtained from the following sources: amoxicillin, SmithKline Beecham; sulphamethoxazole and trimethoprim, Wellcome Research Laboratories; tetracycline and chloramphenicol, Sigma Chemical Company; ofloxacin, Hoechst UK; ciprofloxacin, Bayer UK; and lomefloxacin, GD Searle and Company.
Determination of M i n i m u m Inhibitory Concentrations (MICs) of Antimicrobials MICs of the antimicrobials for all isolates except those of Campylobacterjejuni were determined using an agar incorporation technique in NCCLS approved Mueller-Hinton medium (Oxoid). Using the same technique, the antimicrobial susceptibility of isolates of Campylobacter jejuni was determined in NCCLS approved Mueller-Hinton agar (Oxoid) supplemented
Table 1 shows the in vitro susceptibility of the isolates examined to amoxicillin sulphamethoxazole, trimethoprim, tetracycline, chloramphenicol, ofloxacin, ciprofloxacin, and lomefloxacin. All of the fluoroquinolones examined were very active against the isolates of enteric pathogens examined. Ciprofloxacin was generally the most potent of these compounds, particularly against the Enterobacteriaceae, with all 280 isolates examined inhibited by 0.5 mg/L or less. Lomefloxacin exhibited similar potency to that of ofloxacin with all isolates inhibited by 1 mg/L or less of either compound. By contrast, many of the isolates examined were resistant to one or more of the other, unrelated antimicrobials. No cross-resistance between lomefloxacin and any of the nonfluoroquinolone antimicrobials examined in the study was observed.
TABLE 1 Comparative in vitro Activity of Lomefloxacin Against Bacterial Enteric Pathogens MIC (mg/L) Species
No. of Isolates
Escherichia coli
54
(ETEC, EIEC, EPEC)
Antimicrobial Amoxicillin Sulphamethoxazole Trimethoprim Tetracycline Chloramphenicol Ofloxacin Ciprofloxacin Lomefloxacin
Salmonella spp.
50
Amoxicillin Sulphamethoxazole
50% 4 16 0.25 2 8 0.06 ~0.008 0.06 2 128
90% > 64 >512 0.5 >64 >64 0.06 ~0.008 0.12 > 64 >512
Range 1->64 4->512 0.06-1 1->64 2-~64 0.03-0.25 ~0.008-0.06 0.03-0.5 1->64 16-~512
Lomefloxacin A g a i n s t Enteritis P a t h o g e n s
TABLE 1
341
Continued MIC (rag/L)
Species
Salmonella typhi
No. of Isolates
24
Antimicrobial
40
0.25 4 4 0.12 0.015
Lornefloxacin
0.12
0.12
0.5 32 0.12 1 4 0.03 40.008
1 64 0.25 4 8 0.06 0.015
0.12
0.25
Amoxicillin Sulphamethoxazole Trimethoprim Tetracycline Chloramphenicol Ofloxacin Ciprofloxacin
Amoxicillin Sulphamethoxazole Trimethoprim Tetracycline Chloramphenicol Ofloxacin Ciprofloxacin Lomefloxacin
Yersinia enterocolitica
90%
Trimethoprirn Tetracycline Chloramphenicol Ofloxacin Ciprofloxacin
Lomefloxacin
Shigella spp.
50%
8
>512 >64 >64 4 0.03 40.008
>64 >64 >64 0.12 0.015
>64 >512 >64 >64 64 0.12 40.008
0.06
0.06
Amoxicillin Sulphamethoxazole Trimethoprim Tetracycline Chloramphenicol Ofloxacin Ciprofloxacin
30
Amoxicillin Sulphamethoxazole Trimethoprim Tetracycline Chloramphenicol Ofloxacin Ciprofloxacin Lomefloxacin
Vibrio cholerae
24
Amoxicillin Sulphamethoxazole Trimethoprim Tetracycline Chloramphenicol Ofloxacin Ciprofloxacin Lomefloxacin
0.12->64 2->64 4->64 0.06-0.25 40.008-0.015 0.06-0.12 0.5->64 16->256 0.06->64 1->64 4-32 0.03-0.12 40.008-0.015 0.06-0.25 0.5->64 4->512 0.06->64 2->64 0.5->64 0.03-0.12 40.008-0.015 All at 0.06 1->64 8->512 0.25-4 1-4 1-8 40.008--0.12 40.008-0.015
Lomefloxacin
Campylobacter jejuni
Range
0.015-0.12 8 128 >64 0.5
32 256 >64 >64
4
4
0.25 0.12
0.5 0.25
2->64 16->256 All at >64 0.25->64 2-16 0.12-1 0.06-0.5
0.5
0.5
0.25-1
8
>256 0.5 0.5 1
>64 >256 >64 >64 1
0.015 40.008
0.015 40.008
0.015
0.015
4->64 2->256 0.03->64 0.5-64 0.5-1 40.008-0.015 All at 40.008 40.008-0.015
D. Felmingham and M.J. Robbins
342
TABLE 1
Continued MIC (mg/L)
Species
Vibro parahaemolyticus
No. of Isolates 25
Antimicrobial Amoxicillin Sulphamethoxazole Trimethoprim Tetracycline Chloramphenicol Ofloxacin Ciprofloxacin Lomefloxacin
Aeromonas hydrophila
24
Amoxicillin Sulphamethoxazole Trimethoprim Tetracycline Chloramphenicol Ofloxacin Ciprofloxacin Lomefloxacin
DISCUSSION
The use of antimicrobial chemotherapy for the treatment or prevention of acute diarrhea caused by bacterial enteric pathogens is controversial. Clinical improvement following prompt therapy of shigellosis w i t h compounds such as ampicillin and cotrimoxazole, including a reduction in diarrhea, systemic symptoms, and excretion of the pathogen in feces, has been reported (Haltalin et al., 1967; Tong et al., 1970; Barada and Guerrant, 1980). However, as the disease is usually noninvasive and self-limiting, such treatment is questioned by some because of the rapid selection of bacterial strains characterized by plasmid-mediated resistance to one or more of the commonly used antimicrobials (Farrar and Edison, 1971; Ross et al., 1972). Mujibur et al. (1976) have reported the value of doxycycline in the treatment of cholera and a number of reports have demonstrated antimicrobial prophylaxis to be of value in the prevention of traveler's diarrhea (Dupont et al., 1983; Sack et al., 1978) including a study using norfloxacin, a fluoroquinolone (Wistr6m et al., 1978). In general, oral antimicrobial therapy of diarrhea caused by infection with Salmonella spp., with compounds other than fluoroquinolones, has been shown to have little effect on the course of the disease and in some cases to prolong the carrier state (Rosenstein, 1967). Similarly, a controlled study of the efficacy of erythromycin in the treatment of acute diarrhea caused by Campylobacter spp. showed it to have
50% 62 128 2
90% >64 >256 4
Range
0.25 0.06
0.25 0.12
16-~64 8->256 0.25M 0.5-2 0.5-2 0.008-0.25 ~0.008-0.12
0.25
0.25
0.015-0.5
>64 128 1 1 1 0.015 ~0.008
64->64 8-256 0.25-2 0.5-32 0.5-64 ~0.008-0.12 ~0.008-0.12
0.03
0.015-1
1 1
>64 128 1 0.5 1 0.015 0.008 0.015
1 1
no effect upon the course of the disease, although the organism was eradicated from 100% of the treated patients (Anders et al., 1982). By contrast, studies investigating the use of fluoroquinolones have shown them to be effective not only in treating shigellosis, but also in their ability to reduce the fecal excretion and duration of illness with infections caused by Campylobacter jejuni and Salmonella spp. (Pichler et al., 1987; Dupont et al., 1987). In addition, results obtained from clinical trials of fluoroquinolones for the treatment of typhoid fever suggest that these agents may eventually replace all other treatment regimes for this disease particularly because they appear so effective at complete eradication of the pathogen (Limson, 1986; Ramirez et al., 1985; Diridl et al., 1986). However, enthusiasm for this therapeutic option needs to be tempered in light of reports of clinical failure with the use of ciprofloxacin in the treatment of salmonellosis (particularly where the pretreatment isolate is already resistant to nalidixic acid), and the identification of reduced susceptibility to the fluoroquinolones in vitro amongst isolates of Salmonella spp. and CampyIobacter jejuni (Howard et al., 1990; Piddock et al., 1990; Wray et al., 1990; Endtz et al., 1991). In this study, we have shown that the n e w difluoroquinolone---lomefloxacin, as other members of this class of antimicrobials--is very active against bacterial species that may cause acute infectious diarrhea. In addition, we found no evidence of crossresistance with other, unrelated antibacterial compounds.
Lomefloxacin Against Enteritis Pathogens
Lomefloxacin is well absorbed after oral administration with m a x i m u m serum concentrations of the order of 3 mg/L a n d a half-life of - 7 . 8 hr observed after a dose of 400 m g (Morrison et al., 1988). Furthermore, lomefloxacin has been s h o w n to be present in feces at m e a n concentrations of 89 and 203 mg/kg after 2 and 7 days, respectively, of a course of 400 mg given daily for 7 days to 10 healthy volunteers (Edlund et al., 1990). This regime resulted in selective suppression of the normal aerobic Gram-
343
negative microflora (>3.0 log10 reduction in the n u m b e r of bacteria per gram feces) w i t h o u t the selection of resistant mutants. There was little, or no effect on the aerobic Gram-positive a n d anaerobic microflora. The results of this study, together with the pharmacokinetic observations of others, suggest that lomefloxacin m a y be of clinical value in the treatment or prophylaxis of acute infectious diarrhea of bacterial etiology.
REFERENCES Anders BJ, Laver BA, Paisley JW, Reller LB (1982) Doubleblind placebo controlled trial of erythromycin for the treatment of Campylobacter enteritis. Lancet 1:131-132. Barada FA, Guerrant RL (1980) Sulphamethoxazole-trimethoprim versus ampicillin in treatment of acute invasive diarrhoea in adults. Antimicrob Agents Chemother 17:961-964. Carlson JR, Thornton SA, Dupont HL, West AH, Matthewson JJ (1983) Comparative in vitro activities of ten antimicrobial agents against bacterial enteropathogens. Antimicrob Agents Chemother 24:509-513. Diridl G, Pichler H, Wolf D (1986) Treatment of chronic salmonella carriers with ciprofloxacin. Eur ] Clin Microbiol 5:260-261. Dupont HL, Galindo E, Evans DG, Cabada FJ, Sullivan P, Evans DG Jr (1983) Prevention of traveller's diarrhoea with trimethoprim-sulphamethoxazole (TMP/SMX) and trimethoprim (TMP) alone. Gastroenterology 84:75-80. Dupont HL, Ericsson CD, Robinson A, Johnson PC (1987) Current problems in antimicrobial therapy for bacterial enteric infection. Am J Med 82:(Suppl 4A):324-328. Edlund C, Brismar B, Nord CE (1990) Effect of lomefloxacin on the normal oral and intestinal microflora. Eur J Clin Microbiol Inf Dis 9:35-39. Endtz HP, Ruijs GJ, Von Klingeren B, Jansen WH, Van der Reyden T, Mouton RP (1991) Quinolone resistance in campylobacter isolated from man and poultry following the introduction of fluoroquinolones in veterinary medicine. J Artimicrob Chemother 27:199-208. Farrar WE Jr, Eidson M (1971) Antibiotic resistance to Shigella mediated by R factors. J Infect Dis 123:477-484. Felmingham D, O'Hare MD, Robbins MJ, Wall RA, Williams AH, Cremer AW, Ridgway GL, Grtineberg RN (1985) Comparative in vitro studies with 4-quinolone antimicrobials. Drugs Exp Clin Res 11:317-329. Haltalin KC, Nelson JD, Ring R, Sladoje M, Hinton LV (1967) Double blind treatment study of shigellosis comparing ampicillin, sulphadiazine and placebo. J Pediatr 70:970-981. Howard AJ, Joseph TD, Bloodworth LLO, Frost JA, Chart M, Rowe B (1990) The emergence of ciprofloxacin resistance in Salmonella typhimurium. ] Antimicrob Chemother 26:296-8. Limson BM (1986) Efficacy and safety of ciprofloxacin in
uncomplicated typhoid fever. In Proceedings of the 1st International Ciprofloxacin Workshop. Eds, HC Neu and H Weuta. Amsterdam: Excerpta Medica, p 362. Morrison PJ, Mant TGK, Norman GT, Robinson J, Kunja RL (1988) Pharmacokinetics and tolerance of lomefloxacin after sequentially increasing oral doses. Antimicrob Agents Chemother 32:1503-1507. Mujibur Rahaman M, Majib MA, Jamiul Alam AKM, Rafiqul Islam M (1976) Effects of doxycycline in actively purging cholera patients: a double-blind clinical trial. Antimicrob Agents Chemother 10:610-617. Pichler HET, Diridl G, Stickler K, Wolf D (1987) Clinical efficacy of ciprofloxacin compared with placebo in bacterial diarrhoea. Am J Med 82:(Suppl 4A):329-332. Piddock LJV, Whale K, Wise R (1990) Quinolone resistance in salmonella: clinical experience. Lancet 1:1459. Ramirez CA, Bran JL, Mejia CR, Garcia JF (1985) Open, prospective study of the clinical efficacy of ciprofloxacin. Antimicrob Agents Chemother 28:128-132. Robbins MJ, Baskerville AJ, Sanghrajka M, Mumtaz G, Felmingham D, Ridgway GL, Griineberg RN (1989) Comparative in vitro activity of lomefloxacin, a difluoro-quinolone. Diagn Microbiol Infect Dis 12(Suppl): 65S-76S. Rosenstein BJ (1967) Salmonellosis in infants and children: epidemiological and therapeutic considerations. J Paediatr 70:1-7. Ross S, Controni G, Khan W (1972) Resistance of shigellae to ampicillin and other antibiotics: its clinical and epidemiological implications. JAMA 221:45-47. Sack DA, Kaminsky DC, Sack RB, Itotia JN, Arthur RR, Kapikian AZ, Orskov F, Orskov I (1978) Prophylactic doxycycline for traveller's diarrhoea: results of a prospective double-blind study of Peace Corps volunteers in Kenya. N Engl J Med 298:758-763. Tong MJ, Martin DG, Cunningham JJ, Gunning J (1970) Clinical and bacteriological evaluation of antibiotic treatment in shigellosis. JAMA 214:1841-1844. Wistr6m J, Norrby SR, Burman LG, Lundholm R, Jelheden B, Englund G (1987) Norfloxacin versus placebo for prophylaxis against traveller's diarrhoea. J Antimicrob Chemother 20:563-574. Wray C, McClaren I, Wise R, Piddock LJV (1990) Nalidixic acid-resistant salmonellae. Vet Rec 126:489.
339
In vitro Activity of Lomefloxacin and Other Antimicrobials Against Bacterial Enteritis Pathogens David Felmingham and Marion J. Robbins
Lomefloxacin is a new, difluoroquinolone. In this study, the in vitro activity of lomefloxacin against clinical isolates of a variety of bacterial species associated with acute diarrheal disease was determined and compared with that of ciprofloxacin, ofloxacin, amoxicillin, sulphamethoxazole, trimethoprim, tetracycline, and chloramphenicol. Bacterial isolates were obtained from different geographical areas, including Western Europe and the United Kingdom, Southern Europe, Africa, the Middle East, South and Southeast Asia, and South America, and were included to reflect the range of susceptibility seen throughout the world. Minimum inhibitory concentrations (MICs) were determined using an agar incorporation technique in Mueller-Hinton medium supplemented when neces-
sary with saponin-lysed horse blood at a final concentration of 10% vol/vol. Lomefloxacin was highly active against all the species examined which included Salmonella spp., Shigella spp., Escherichia coli enterotoxigenic [(ETEC), enteroinvasive (EIEC), and enteropathogenic (EPEC) strains], Yersinia enterocolitica, Campylobacter jejuni, Vibrio spp., and Aeromonas hydrophila, with all isolates inhibited by 1 mg/L or less. This activity was similar to ofloxacin and slightly less than that of ciprofloxacin. By contrast, many of the isolates were resistant to one or more of the other, unrelated animicrobials. No cross-resistance between lomefloxacin and any of the nonfluoroquinolone antimicrobials examined in the study was observed.
INTRODUCTION
In a previous study of the susceptibility of a variety of bacterial enteropathogens to 10 antimicrobials, including ampicillin, cotrimoxazole, and doxycycline, Carlson et al. (1983) concluded that the most active agents of those examined were the two fluoroquinolones, enoxacin and norfloxacin. More recently, Felmingham et al. (1985), in a study of the activity of twelve 4-quinolones against bacterial enteric pathogens, showed that all of the new fluoroquinolones, including enoxacin and norfloxacin, were highly active with ofloxacin and ciprofloxacin possessing the greatest potency. In this study, we have determined the in vitro activity of lomefloxacin (1-ethyl-6,8-difluoro-l,4dihydro7-(3-methyl-l-piperazinyl)-4-oxo quinoline3-carboxylic acid monohydrochloride), a new difluoroquinolone with a broad and potent spectrum of antibacterial activity (Robbins et al., 1989), against a variety of bacterial species associated with acute diarrheal disease and compared it with that of amoxicillin, sulphamethoxazole, trimethoprim, tetracycline, and chloramphenicol.
Acute diarrheal disease, caused by bacterial, viral, or parasitic infection, is a worldwide problem. However, the greatest morbidity and mortality is seen in the developing countries of Africa, the Middle East, South and Southeast Asia, and South America, where the infections are most frequently of bacterial etiology. The bacterial species associated with acute infectious diarrhea include Escherichia coli [Enterotoxigenic (ETEC), enteroinvasive (EIEC), and enteropathogenic (EPEC) strains], Salmonella spp., Shigella spp., Yersinia enterocolitica, Campylobacter jejuni, Vibrio cholerae, V ibrio parahaemolyticus , and Aeromonas hydrophila.
From the Department of Clinical Microbiology,University of College Hospital, London, England. Address reprint requests to D. Felmingham, Department of Clinical Microbiology,University College Hospital, Grafton Way, London WCIE 6AU, England, UK. Received 2 April 1991, revised and accepted 1 July 1991. © 1992Elsevier Science Publishing Co., Inc. 655 Avenue of the Americas, New York, NY 10010 0732-8893/92/$5. O0
340
D. Felmingham and M.J. Robbins
MATERIALS A N D M E T H O D S Bacterial Isolates Bacterial isolates used in this study were derived from clinical material examined in the Department of Clinical Microbiology at University College Hospital, London, supplemented with strains from Southern Europe, Africa, the Middle East, South and Southeast Asia, and South America kindly supplied by colleagues at the Hospital for Tropical Diseases, London and the London School of Hygiene and Tropical Medicine. The collection of bacteria studied was designed to reflect the range of antimicrobial susceptibility seen throughout the world and not to represent that seen in defined epidemiological populations.
with saponin-lysed horse blood (Tissue Culture Services) to a final concentration of 10% volYvol. The inoculum used was approximately 104 colony forming units (CFU) of each isolate, contained in 1 p~l. Following inoculation, plates were incubated in air at 37°C for 18-24 hr except those inoculated with the isolates of Campylobacter jejuni, which were incubated microaerophilically (BBL Camypak System) at 37°C for 48 hr. MICs were determined as the lowest concentration of antimicrobial tested that completely inhibited macroscopically visible surface growth of the inoculum after reference to an antimicrobial-free control plate. Escherichia coli (NCTC 10418) and Staphylococcus aureus (NCTC 6571) were included throughout as control bacterial strains.
Antimicrobials RESULTS Substances of known potency were obtained from the following sources: amoxicillin, SmithKline Beecham; sulphamethoxazole and trimethoprim, Wellcome Research Laboratories; tetracycline and chloramphenicol, Sigma Chemical Company; ofloxacin, Hoechst UK; ciprofloxacin, Bayer UK; and lomefloxacin, GD Searle and Company.
Determination of M i n i m u m Inhibitory Concentrations (MICs) of Antimicrobials MICs of the antimicrobials for all isolates except those of Campylobacterjejuni were determined using an agar incorporation technique in NCCLS approved Mueller-Hinton medium (Oxoid). Using the same technique, the antimicrobial susceptibility of isolates of Campylobacter jejuni was determined in NCCLS approved Mueller-Hinton agar (Oxoid) supplemented
Table 1 shows the in vitro susceptibility of the isolates examined to amoxicillin sulphamethoxazole, trimethoprim, tetracycline, chloramphenicol, ofloxacin, ciprofloxacin, and lomefloxacin. All of the fluoroquinolones examined were very active against the isolates of enteric pathogens examined. Ciprofloxacin was generally the most potent of these compounds, particularly against the Enterobacteriaceae, with all 280 isolates examined inhibited by 0.5 mg/L or less. Lomefloxacin exhibited similar potency to that of ofloxacin with all isolates inhibited by 1 mg/L or less of either compound. By contrast, many of the isolates examined were resistant to one or more of the other, unrelated antimicrobials. No cross-resistance between lomefloxacin and any of the nonfluoroquinolone antimicrobials examined in the study was observed.
TABLE 1 Comparative in vitro Activity of Lomefloxacin Against Bacterial Enteric Pathogens MIC (mg/L) Species
No. of Isolates
Escherichia coli
54
(ETEC, EIEC, EPEC)
Antimicrobial Amoxicillin Sulphamethoxazole Trimethoprim Tetracycline Chloramphenicol Ofloxacin Ciprofloxacin Lomefloxacin
Salmonella spp.
50
Amoxicillin Sulphamethoxazole
50% 4 16 0.25 2 8 0.06 ~0.008 0.06 2 128
90% > 64 >512 0.5 >64 >64 0.06 ~0.008 0.12 > 64 >512
Range 1->64 4->512 0.06-1 1->64 2-~64 0.03-0.25 ~0.008-0.06 0.03-0.5 1->64 16-~512
Lomefloxacin A g a i n s t Enteritis P a t h o g e n s
TABLE 1
341
Continued MIC (rag/L)
Species
Salmonella typhi
No. of Isolates
24
Antimicrobial
40
0.25 4 4 0.12 0.015
Lornefloxacin
0.12
0.12
0.5 32 0.12 1 4 0.03 40.008
1 64 0.25 4 8 0.06 0.015
0.12
0.25
Amoxicillin Sulphamethoxazole Trimethoprim Tetracycline Chloramphenicol Ofloxacin Ciprofloxacin
Amoxicillin Sulphamethoxazole Trimethoprim Tetracycline Chloramphenicol Ofloxacin Ciprofloxacin Lomefloxacin
Yersinia enterocolitica
90%
Trimethoprirn Tetracycline Chloramphenicol Ofloxacin Ciprofloxacin
Lomefloxacin
Shigella spp.
50%
8
>512 >64 >64 4 0.03 40.008
>64 >64 >64 0.12 0.015
>64 >512 >64 >64 64 0.12 40.008
0.06
0.06
Amoxicillin Sulphamethoxazole Trimethoprim Tetracycline Chloramphenicol Ofloxacin Ciprofloxacin
30
Amoxicillin Sulphamethoxazole Trimethoprim Tetracycline Chloramphenicol Ofloxacin Ciprofloxacin Lomefloxacin
Vibrio cholerae
24
Amoxicillin Sulphamethoxazole Trimethoprim Tetracycline Chloramphenicol Ofloxacin Ciprofloxacin Lomefloxacin
0.12->64 2->64 4->64 0.06-0.25 40.008-0.015 0.06-0.12 0.5->64 16->256 0.06->64 1->64 4-32 0.03-0.12 40.008-0.015 0.06-0.25 0.5->64 4->512 0.06->64 2->64 0.5->64 0.03-0.12 40.008-0.015 All at 0.06 1->64 8->512 0.25-4 1-4 1-8 40.008--0.12 40.008-0.015
Lomefloxacin
Campylobacter jejuni
Range
0.015-0.12 8 128 >64 0.5
32 256 >64 >64
4
4
0.25 0.12
0.5 0.25
2->64 16->256 All at >64 0.25->64 2-16 0.12-1 0.06-0.5
0.5
0.5
0.25-1
8
>256 0.5 0.5 1
>64 >256 >64 >64 1
0.015 40.008
0.015 40.008
0.015
0.015
4->64 2->256 0.03->64 0.5-64 0.5-1 40.008-0.015 All at 40.008 40.008-0.015
D. Felmingham and M.J. Robbins
342
TABLE 1
Continued MIC (mg/L)
Species
Vibro parahaemolyticus
No. of Isolates 25
Antimicrobial Amoxicillin Sulphamethoxazole Trimethoprim Tetracycline Chloramphenicol Ofloxacin Ciprofloxacin Lomefloxacin
Aeromonas hydrophila
24
Amoxicillin Sulphamethoxazole Trimethoprim Tetracycline Chloramphenicol Ofloxacin Ciprofloxacin Lomefloxacin
DISCUSSION
The use of antimicrobial chemotherapy for the treatment or prevention of acute diarrhea caused by bacterial enteric pathogens is controversial. Clinical improvement following prompt therapy of shigellosis w i t h compounds such as ampicillin and cotrimoxazole, including a reduction in diarrhea, systemic symptoms, and excretion of the pathogen in feces, has been reported (Haltalin et al., 1967; Tong et al., 1970; Barada and Guerrant, 1980). However, as the disease is usually noninvasive and self-limiting, such treatment is questioned by some because of the rapid selection of bacterial strains characterized by plasmid-mediated resistance to one or more of the commonly used antimicrobials (Farrar and Edison, 1971; Ross et al., 1972). Mujibur et al. (1976) have reported the value of doxycycline in the treatment of cholera and a number of reports have demonstrated antimicrobial prophylaxis to be of value in the prevention of traveler's diarrhea (Dupont et al., 1983; Sack et al., 1978) including a study using norfloxacin, a fluoroquinolone (Wistr6m et al., 1978). In general, oral antimicrobial therapy of diarrhea caused by infection with Salmonella spp., with compounds other than fluoroquinolones, has been shown to have little effect on the course of the disease and in some cases to prolong the carrier state (Rosenstein, 1967). Similarly, a controlled study of the efficacy of erythromycin in the treatment of acute diarrhea caused by Campylobacter spp. showed it to have
50% 62 128 2
90% >64 >256 4
Range
0.25 0.06
0.25 0.12
16-~64 8->256 0.25M 0.5-2 0.5-2 0.008-0.25 ~0.008-0.12
0.25
0.25
0.015-0.5
>64 128 1 1 1 0.015 ~0.008
64->64 8-256 0.25-2 0.5-32 0.5-64 ~0.008-0.12 ~0.008-0.12
0.03
0.015-1
1 1
>64 128 1 0.5 1 0.015 0.008 0.015
1 1
no effect upon the course of the disease, although the organism was eradicated from 100% of the treated patients (Anders et al., 1982). By contrast, studies investigating the use of fluoroquinolones have shown them to be effective not only in treating shigellosis, but also in their ability to reduce the fecal excretion and duration of illness with infections caused by Campylobacter jejuni and Salmonella spp. (Pichler et al., 1987; Dupont et al., 1987). In addition, results obtained from clinical trials of fluoroquinolones for the treatment of typhoid fever suggest that these agents may eventually replace all other treatment regimes for this disease particularly because they appear so effective at complete eradication of the pathogen (Limson, 1986; Ramirez et al., 1985; Diridl et al., 1986). However, enthusiasm for this therapeutic option needs to be tempered in light of reports of clinical failure with the use of ciprofloxacin in the treatment of salmonellosis (particularly where the pretreatment isolate is already resistant to nalidixic acid), and the identification of reduced susceptibility to the fluoroquinolones in vitro amongst isolates of Salmonella spp. and CampyIobacter jejuni (Howard et al., 1990; Piddock et al., 1990; Wray et al., 1990; Endtz et al., 1991). In this study, we have shown that the n e w difluoroquinolone---lomefloxacin, as other members of this class of antimicrobials--is very active against bacterial species that may cause acute infectious diarrhea. In addition, we found no evidence of crossresistance with other, unrelated antibacterial compounds.
Lomefloxacin Against Enteritis Pathogens
Lomefloxacin is well absorbed after oral administration with m a x i m u m serum concentrations of the order of 3 mg/L a n d a half-life of - 7 . 8 hr observed after a dose of 400 m g (Morrison et al., 1988). Furthermore, lomefloxacin has been s h o w n to be present in feces at m e a n concentrations of 89 and 203 mg/kg after 2 and 7 days, respectively, of a course of 400 mg given daily for 7 days to 10 healthy volunteers (Edlund et al., 1990). This regime resulted in selective suppression of the normal aerobic Gram-
343
negative microflora (>3.0 log10 reduction in the n u m b e r of bacteria per gram feces) w i t h o u t the selection of resistant mutants. There was little, or no effect on the aerobic Gram-positive a n d anaerobic microflora. The results of this study, together with the pharmacokinetic observations of others, suggest that lomefloxacin m a y be of clinical value in the treatment or prophylaxis of acute infectious diarrhea of bacterial etiology.
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