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Epidemiology of Aeromonas species in a hospital
Journal
of Hospital
Infection
Epidemiology
11, 169-l 75
of Aeromonas
S. E. Millership*, *Public
(1988)
species
J. R. Stephensont
in a hospital
and S. Tabaqchalit
Health Laboratory, Whipps Cross Hospital, London El1 and TDept. of Microbiology, St Bartholomew’s Hospital, London EC1 Accepted for publication
3 June 1987
Summary: The occurrence of Aeromonas spp. in a hospital water supply, in patients and in the local community was investigated. In healthy persons outside the hospital the isolation rate was 3.6% and among hospital patients it was 6%. Seven per cent of water samples yielded aeromonas strains. Isolates were typed by sodium dodecyl sulphate polyacrylamide gel electrophoresis of sulphur-35 methionine labelled proteins of aeromonas isolates. No relationship between water and human isolates could be established, even when a strain of A. hydrophilu producing Vero cell cytotoxin contaminated enteral feeds given to patients in the intensive care unit. Key words: Aeromonas;
hospital
water
Introduction
It is well established that Aeromonas spp. may cause septicaemia, especially in immunocompromised patients (Abrams, Zierdt & Brown, 1971; Janda, Reitano & Bottone, 1984), biliary tract infections (von Graevenitz 8z Mensch, 1968) and wound infections following contact with contaminated water (McCraken & Barkley, 1972; Washington, 1972). There is also evidence that some strains may cause acute gastroenteritis (Gracey, Burke & Robinson, 1982; Millership, Barer & Tabaqchali, 1986) which is occasionally severe and prolonged (Janda et al., 1983; Agger, McCormick & Gurwith, 1985). For this reason in particular it is important to establish the relationship between strains found in the water supply and those from patients with diarrhoea. Aeromonas spp. have been found in chlorinated drinking water throughout the world (Hazen et al., 1978; Burke et al., 1984), including the UK (Millership & Chattopadhyay, 198.5) and it is possible that they are able to survive treatment regarded at present as sufficient to render the water safe to drink (Burke et al., 1984). Clusters of isolates occurring in hospitals have been described (Cookson, Houang & Lee 1984; Picard & Goullet 1984). However, most laboratories Correspondence to Dr S. E. Millership, Dept. of Bacteriology, Hammersmith Hospital, Ducane Road, London W12 OHS. 01954701/88/020169+07
$03.00/O
Royal Postgraduate
Medical
0 1988 The Hospital
169
Infection
School,
Society
170
S. E. Millership
et al.
do not use selective media for the isolation of aeromonas and no generally accepted typing method is available. Thus very little is known about the epidemiology of this organism in hospitals. The present study was undertaken to examine this question using a newly described typing method, based on sodium dodecyl sulphate polyacrylamide gel electrophoresis of radiolabelled proteins of aeromonas (Stephenson, Millership & Tabaqchali, in press). Materials
and methods
The complete study took place over 20 months in a district general hospital with 750 beds. In two periods between May 1982 to August 1983, all faecal samples from hospital in-patients and the community submitted to the laboratory were examined for aeromonas. The latter specimens were obtained from three sources: food handlers screened prior to starting work, asymptomatic contacts of persons with salmonellas or shigellas who did not have faecal pathogens isolated and healthy persons investigated during the course of outbreaks of gastrointestinal disease. In the last case, environmental health officers usually collected samples from all members of an affected institution, regardless of symptoms. All those in whom no pathogens were found and who remained asymptomatic throughout the investigation were called ‘healthy’ for the purpose of the present study. Water samples from taps and tanks throughout the hospital received in the laboratory between July 1983 and February 1984 were examined for aeromonas. In September and October 1983 the intensive care unit was studied in more detail. Samples were taken weekly from all taps, drains and draining boards and on alternate days, as far as possible, from humidifiers, ventilator tubing, suction apparatus and patient feeds. Nose, throat, sputum, umbilical, perineal, rectal and urine specimens were taken on at least five days each week from all patients. A record was kept of any change in the clinical condition of patients. Primary isolation of aeromonads from faeces and water samples was by methods previously described (Millership, Curnow & Chattopadhyay 1983; Millership & Chattopadhyay, 1985). In brief, faecal samples (l-2 g approx.) were enriched in 10 ml alkaline peptone water (pH 8.6) which was incubated overnight at room temperature, then subcultured to xylose deoxycholate citrate agar (XDCA) or bile salts brilliant green (BBG) agar. Water (l&l 00 ml) samples were either filtered through an 0.45 l.t millipore membrane cultured on BBG agar incubated anaerobically, or 2ml was added to 20 ml alkaline peptone water which was treated as above. All other specimens were cultured by conventional methods. Swabs and 2 ml liquid samples other than from the water supply were additionally enriched in 10 ml nutrient broth incubated overnight at 37°C and subcultured to horse blood and MacConkey agars.
Aeromonas Table
Aesculin breakdown Gas production beta haemolysis Growth at 42°C Fermentation of arabinose Fermentation of salicin Acetoin production
I. DifJerentiation
171
spp. in a hospital
of the species of Aeromonas sobria
Aeromonas hydrophila
caviae
+ + + +
+ + + + + +
+ + + -
Oxidase positive colonies were identified using AP120E and vibriostatic agent O/129. Aeromonas isolates were further identified to species level seven biochemical tests as previously described (Barer, Millership & Tabaqchali, 1986). The breakdown of aesculin, fermentation of arabinose and salicin, gas production from glucose and acetoin production were examined by standard methods. Beta haemolysis was examined on horse blood agar after 18 h incubation at 37”C, and growth at 42°C on horse blood agar compared with that of single colonies at 37°C. Species were identified as shown in Table I. Strains were typed using sodium dodecyl sulphate polyacrylamide gel electrophoresis (SDS-PAGE) of sulphur-35 labelled proteins (Stephenson et al. in press). In brief, overnight cultures of isolates grown on horse blood agar were inoculated into Methionine Assay Medium (Difco) containing 35S methionine (Amersham International). After incubation for 2 h at 37°C double strength sample buffer (Laemmli, 1970) was added and the samples boiled for 3 min SDS-PAGE was performed according to Laemmli (1970) and autoradiographs of the fixed gels developed after 24 h exposure. The protein profiles of each pair of isolates within an experiment were compared visually and the Dice coefficient calculated (Dice, 1945). Pairs of isolates were considered indistinguishable if they were more than 80% related and definitely different if less than 70% related in the species caviae and hydrophila. All pairs in the species sobriu were considered definitely different if the similarity coefficient was less than SO%, and above this to be indistinguishable. Using these criteria at least 75% of all pairs expected to be different on epidemiological grounds were considered to be distinguishable and the results were reproducible within acceptable limits. All isolates were tested for the production of cytotoxin in vitro (Barer et al., 1986). Overnight broth cultures shaken at 100-200 rpm were centrifuged and filtered. The filtrate was added to Vero cell monolayers in microtitre trays and cytotoxic effects were observed after incubation overnight at 37°C.
172
S. E. Millership
et al.
Results
In 1982 faecal samples were received from 118 hospital inpatients, of whom seven (6.0%) had aeromonas. Three isolates were A. caviae, two A. hydrophila, one A. sobria and one a strain not classifiable in any of these species. One A. hydrophila and the A. sobria isolates were cytotoxin producing. A further five isolates were recovered from the faeces of hospital patients in 1983 of which two were A. caviue, and three were cytotoxigenic A. sobria. In the community six of 169 (3.6%) persons had aeromonas species (four A. caviue, one non-toxigenic A. hydrophilu, one toxigenic A. sobriu). There was no significant difference between isolation rates from the community or hospital inpatients (x2 = O-91; 0.8 P> O-5). Fifty-seven water samples were examined of which seven (12 per cent) had aeromonas. An isolate of A. caviue and single toxin-producing isolates of A. hydrophilu and A. sobriu were recovered from tanks. One isolate of A. caviae, one toxin-positive A. hydrophilu and two isolates not classifiable into any of the named species were found in tap samples. The detailed study of the intensive care unit yielded ten environmental of which two were cytotoxin-producing A. isolates of aeromonas, hydrophilu and eight A. caviue. Both A. hydrophilu isolates were recovered in mixed culture at the end of the infusion period from two different whole protein nasogastric feeds given to patients. Two weeks after the end of the study period cytotoxin-producing A. hydrophila was again isolated, this time from nasogastric suction apparatus. One environmental isolate of A. cuviue was found in a nasogastric feed. The other seven isolates came from the tap, drain or draining board of the kitchen in the unit which was used for the preparation of patient’s feeds. The only aeromonads recovered from patients were two isolates of A. cuviue. The first isolate was cultured from the throat swab of a patient after 24 h on the unit at the time of discharge. Ten days later screening swabs on re-admission were negative. A second patient had A. cuviue in perineal and rectal swabs 18 days after admission to the unit. The samples were taken 8 days after recovery of the first aeromonas isolate. Subsequent samples from this patient for the remainder of the study period were negative. No patient had diarrhoea solely attributable to aeromonas. The relationships of all isolates from the hospital are illustrated in Figure 1. No environmental strain was detected in any patient throughout the study. A total of 19 different strains of the three named species among 32 isolates were identified. In the intensive care unit the kitchen tap, drain or draining board yielded the same strain of A. cuviae on five occasions, plus two other strains. A feed had a further strain of A. cuviue. Both patient isolates of A. cuviae were distinguishable. Six A. hydrophila isolates in the hospital water supply and on the intensive care unit from intragastric feeds and nasogastric aspiration bottles were all identical. All isolates of A. sobriu were different.
spp. in a hospital
Aeromonas Specimens
sampled;
173
Waters i ITU
Faeces
I
I
t
Other
Aeromonos
M
J
J
A
.
sobria
.
.
MJJASONDJF
1982
1983 Calendar
1984
months
Strains of Aeromonus isolated from humans and the hospital environment. n , Human isolates; A, Water isolates; 0, Other environmental isolates. Each horizontal line represents isolates of a single strain.
Discussion
This study illustrates the level of colonization of patients and the environment in a hospital by Aeromonas spp. in the absence of any outbreak. No previous study of this kind has been done. It is notable that with the use of special isolation techniques aeromonads appear to be not uncommon. However, unlike some other gram-negative organisms (Cross, 1985) the isolation rate is not greatly increased by admission to hospital. As in previous studies of clusters of cases we have found considerable heterogeneity among the aeromonads isolated. The hospital is in an old building and it was impossible to establish with certainty the plumbing connections throughout the building. We have therefore assumed that, although some areas were mainly supplied by a particular tank, there were potential connections between all parts of the system and patients were at risk of acquiring any strain of aeromonas found in any part of the water system. The strains probably came from different
174
S. E. Millership
et al.
sources. Some may have been present in the water distribution system (Hazen et al., 1979; Burke et al., 1984; Stephenson et al., in press), other strains may have been introduced by contamination of the tank (Millership & Chattopadhyay, 1985) and yet others by local contamination of taps. The most striking finding from our study is the lack of relationship between water and human isolates. Also, if aeromonads were acquired from drinking water it might be expected that different patients would have indistinguishable isolates, but this is not the case. There is some evidence that A. caviae is non-pathogenic in the gut (Figura et al., 1986) whereas the species producing cytotoxin are likely to cause diarrhoea (Cumberbatch, et al., 1979; Millership, et al., in press). It is therefore surprising that toxigenic strains, which were administered to patients on gastric acid inhibitors by enteral feed, were not detected in faeces, nor was any change in the patient’s clinical condition observed. It therefore seems that the isolation of Aeromonas sp. from a water supply or the environment does not necessarily imply that there is a risk of diarrhoeal disease. It is likely that more than one virulence factor is involved in the production of gastroenteritis, as is often the case with other alimentary pathogens when acquired from drinking water or foods. References Abrams, E., Zierdt, C. H. & Brown, J. A. (1971). Observations on Aeromonas hydrophila septicaemia in a patient with leukaemia. Journal of Clinical Pathology 24, 491427. Agger, W. A., McCormick, J. D. & Gurwith, M. (1985). Clinical and microbiological features of Aeromonas hydrophila-associated diarrhoea. Journal of Clinical Microbiology
21,909-913. Barer, M. R., Millership, S. E. & Tabaqchali, S. (1986). Relationship of toxin production to species of the genus Aeromonas. Journal of Medical Microbiology 22, 3033310. Burke, V., Robinson, J., Gracey, M., Peterson, D. & Partridge, K. (1984). Isolation of Aeromonas hydrophilu from a metropolitan water supply: seasonal correlation with clinical isolates. Applied and Environmental Microbiology 48, 361-366. Cookson, B. D., Houang, E. T. & Lee, J. V. (1984). The use of a biotyping system to investigate an unusual clustering of bacteremias caused by Aeromonas species. Journal of Hospital Infection 5, 205-209. Cross, A. S. (1985). Evolving epidemiology of Pseudomonas aeruginosa infections. European Journal of Clinical Microbiology 44, 156-159. Cumberbatch, N., Gurwith, M. J., Langston, C., Sack, R. B. & Brunton, J. L. (1979). Cytotoxic enterotoxin produced by Aeromonas hydrophila: relationship of toxigenic isolates to diarrhoeal disease. Infection and Immunity 23, 829-837. Dice, L. R. (1945). Measures of the amount of ecologic association between species. Ecology 26, 297-302. S., Ceccherini, C. & Bereri, A. (1986). Prevalence, species Figura, N., Marri, L., Verdiani, differentiation and toxigenicity of Aeromonas strains in cases of childhood gastro-enteritis and in controls. Journal of Clinical Microbiology 23, 595-599. gastroenteritis. Lancet Gracey, M., Burke, V. & Robinson, J. (1982). A eromonas-associated
ii, 1304-l 306. von Graeventiz A. & Mensch, A. H. (1968). The genus Aeromonas in human bacteriology. Report of 30 cases and review of the literature. New EnglandJournal of Medicine 278, 245-249. Hazen, T. C., Fliermans, C. B., Hirsch, R. P. & Esch, G. (1978). Prevalence and distribution of Aeromonas hydrophila in the United States. Applied and Environmental Microbiology 36, 731-738.
Aeromonas
spp. in a hospital
175
Janda, J. M., Bottone, E. J., Skinner, C. V. & Calcaterra, D. (1983). Phenotypic markers associated with gastrointestinal Aeromonas hydrophila isolates from symptomatic children. Journal of Clinical Microbiology 17, 588-591. Janda, J. M., Reitano, M. & Bottone, E. J. (1984). Biotyping of Aeromonas isolates as a correlate to delineating a species-associated disease spectrum. Journal of Clinical iMicrobiology 19, 44-47. Laemmli, U. K. (1970). Cleavage of structural proteins during assembly of the head of bacteriophage T4. Nature 227, 68&685. McCraken, A. W. & Barkley, R. (1972). Isolation of Aeromonas species from clinical sources. Journal of Clinical Pathology 25, 970-975. Millership, S. E., Barer, M. R. & Tabaqchali, S. (1986). Toxin production by Aeromonas spp from different sources. Journal of Medical Microbiology. (In press.) Millership, S. E. & Chattopadhyay B. (1985). Aeromonas hydrophila in chlorinated water supplies. Journal of Hospital Infection 6, 75-80. Millership, S. E., Curnow, S. & Chattopadhyay, B. (1983). F aecal carriage rate of Aeromonas hydrophila. Journal of Clinical Pathology 36, 926923. Picard, B. & Goullet, P. H. (1984). Letter. Journal of Hospital Infection 5, 335-336. Stephenson, J. R., Millership, S. E. & Tabaqchali, S. (1986). Typing of Aeromonas species by polyacrylamide gel electrophoresis of radiolabelled cellular proteins. Journal of Medical Microbiology. (In press.) Washington, J. A. 1972). Aeromonas hydrophila in clinical bacteriologic specimens. Annals of Internal Medicine 76, 611-614.
of Hospital
Infection
Epidemiology
11, 169-l 75
of Aeromonas
S. E. Millership*, *Public
(1988)
species
J. R. Stephensont
in a hospital
and S. Tabaqchalit
Health Laboratory, Whipps Cross Hospital, London El1 and TDept. of Microbiology, St Bartholomew’s Hospital, London EC1 Accepted for publication
3 June 1987
Summary: The occurrence of Aeromonas spp. in a hospital water supply, in patients and in the local community was investigated. In healthy persons outside the hospital the isolation rate was 3.6% and among hospital patients it was 6%. Seven per cent of water samples yielded aeromonas strains. Isolates were typed by sodium dodecyl sulphate polyacrylamide gel electrophoresis of sulphur-35 methionine labelled proteins of aeromonas isolates. No relationship between water and human isolates could be established, even when a strain of A. hydrophilu producing Vero cell cytotoxin contaminated enteral feeds given to patients in the intensive care unit. Key words: Aeromonas;
hospital
water
Introduction
It is well established that Aeromonas spp. may cause septicaemia, especially in immunocompromised patients (Abrams, Zierdt & Brown, 1971; Janda, Reitano & Bottone, 1984), biliary tract infections (von Graevenitz 8z Mensch, 1968) and wound infections following contact with contaminated water (McCraken & Barkley, 1972; Washington, 1972). There is also evidence that some strains may cause acute gastroenteritis (Gracey, Burke & Robinson, 1982; Millership, Barer & Tabaqchali, 1986) which is occasionally severe and prolonged (Janda et al., 1983; Agger, McCormick & Gurwith, 1985). For this reason in particular it is important to establish the relationship between strains found in the water supply and those from patients with diarrhoea. Aeromonas spp. have been found in chlorinated drinking water throughout the world (Hazen et al., 1978; Burke et al., 1984), including the UK (Millership & Chattopadhyay, 198.5) and it is possible that they are able to survive treatment regarded at present as sufficient to render the water safe to drink (Burke et al., 1984). Clusters of isolates occurring in hospitals have been described (Cookson, Houang & Lee 1984; Picard & Goullet 1984). However, most laboratories Correspondence to Dr S. E. Millership, Dept. of Bacteriology, Hammersmith Hospital, Ducane Road, London W12 OHS. 01954701/88/020169+07
$03.00/O
Royal Postgraduate
Medical
0 1988 The Hospital
169
Infection
School,
Society
170
S. E. Millership
et al.
do not use selective media for the isolation of aeromonas and no generally accepted typing method is available. Thus very little is known about the epidemiology of this organism in hospitals. The present study was undertaken to examine this question using a newly described typing method, based on sodium dodecyl sulphate polyacrylamide gel electrophoresis of radiolabelled proteins of aeromonas (Stephenson, Millership & Tabaqchali, in press). Materials
and methods
The complete study took place over 20 months in a district general hospital with 750 beds. In two periods between May 1982 to August 1983, all faecal samples from hospital in-patients and the community submitted to the laboratory were examined for aeromonas. The latter specimens were obtained from three sources: food handlers screened prior to starting work, asymptomatic contacts of persons with salmonellas or shigellas who did not have faecal pathogens isolated and healthy persons investigated during the course of outbreaks of gastrointestinal disease. In the last case, environmental health officers usually collected samples from all members of an affected institution, regardless of symptoms. All those in whom no pathogens were found and who remained asymptomatic throughout the investigation were called ‘healthy’ for the purpose of the present study. Water samples from taps and tanks throughout the hospital received in the laboratory between July 1983 and February 1984 were examined for aeromonas. In September and October 1983 the intensive care unit was studied in more detail. Samples were taken weekly from all taps, drains and draining boards and on alternate days, as far as possible, from humidifiers, ventilator tubing, suction apparatus and patient feeds. Nose, throat, sputum, umbilical, perineal, rectal and urine specimens were taken on at least five days each week from all patients. A record was kept of any change in the clinical condition of patients. Primary isolation of aeromonads from faeces and water samples was by methods previously described (Millership, Curnow & Chattopadhyay 1983; Millership & Chattopadhyay, 1985). In brief, faecal samples (l-2 g approx.) were enriched in 10 ml alkaline peptone water (pH 8.6) which was incubated overnight at room temperature, then subcultured to xylose deoxycholate citrate agar (XDCA) or bile salts brilliant green (BBG) agar. Water (l&l 00 ml) samples were either filtered through an 0.45 l.t millipore membrane cultured on BBG agar incubated anaerobically, or 2ml was added to 20 ml alkaline peptone water which was treated as above. All other specimens were cultured by conventional methods. Swabs and 2 ml liquid samples other than from the water supply were additionally enriched in 10 ml nutrient broth incubated overnight at 37°C and subcultured to horse blood and MacConkey agars.
Aeromonas Table
Aesculin breakdown Gas production beta haemolysis Growth at 42°C Fermentation of arabinose Fermentation of salicin Acetoin production
I. DifJerentiation
171
spp. in a hospital
of the species of Aeromonas sobria
Aeromonas hydrophila
caviae
+ + + +
+ + + + + +
+ + + -
Oxidase positive colonies were identified using AP120E and vibriostatic agent O/129. Aeromonas isolates were further identified to species level seven biochemical tests as previously described (Barer, Millership & Tabaqchali, 1986). The breakdown of aesculin, fermentation of arabinose and salicin, gas production from glucose and acetoin production were examined by standard methods. Beta haemolysis was examined on horse blood agar after 18 h incubation at 37”C, and growth at 42°C on horse blood agar compared with that of single colonies at 37°C. Species were identified as shown in Table I. Strains were typed using sodium dodecyl sulphate polyacrylamide gel electrophoresis (SDS-PAGE) of sulphur-35 labelled proteins (Stephenson et al. in press). In brief, overnight cultures of isolates grown on horse blood agar were inoculated into Methionine Assay Medium (Difco) containing 35S methionine (Amersham International). After incubation for 2 h at 37°C double strength sample buffer (Laemmli, 1970) was added and the samples boiled for 3 min SDS-PAGE was performed according to Laemmli (1970) and autoradiographs of the fixed gels developed after 24 h exposure. The protein profiles of each pair of isolates within an experiment were compared visually and the Dice coefficient calculated (Dice, 1945). Pairs of isolates were considered indistinguishable if they were more than 80% related and definitely different if less than 70% related in the species caviae and hydrophila. All pairs in the species sobriu were considered definitely different if the similarity coefficient was less than SO%, and above this to be indistinguishable. Using these criteria at least 75% of all pairs expected to be different on epidemiological grounds were considered to be distinguishable and the results were reproducible within acceptable limits. All isolates were tested for the production of cytotoxin in vitro (Barer et al., 1986). Overnight broth cultures shaken at 100-200 rpm were centrifuged and filtered. The filtrate was added to Vero cell monolayers in microtitre trays and cytotoxic effects were observed after incubation overnight at 37°C.
172
S. E. Millership
et al.
Results
In 1982 faecal samples were received from 118 hospital inpatients, of whom seven (6.0%) had aeromonas. Three isolates were A. caviae, two A. hydrophila, one A. sobria and one a strain not classifiable in any of these species. One A. hydrophila and the A. sobria isolates were cytotoxin producing. A further five isolates were recovered from the faeces of hospital patients in 1983 of which two were A. caviue, and three were cytotoxigenic A. sobria. In the community six of 169 (3.6%) persons had aeromonas species (four A. caviue, one non-toxigenic A. hydrophilu, one toxigenic A. sobriu). There was no significant difference between isolation rates from the community or hospital inpatients (x2 = O-91; 0.8 P> O-5). Fifty-seven water samples were examined of which seven (12 per cent) had aeromonas. An isolate of A. caviue and single toxin-producing isolates of A. hydrophilu and A. sobriu were recovered from tanks. One isolate of A. caviae, one toxin-positive A. hydrophilu and two isolates not classifiable into any of the named species were found in tap samples. The detailed study of the intensive care unit yielded ten environmental of which two were cytotoxin-producing A. isolates of aeromonas, hydrophilu and eight A. caviue. Both A. hydrophilu isolates were recovered in mixed culture at the end of the infusion period from two different whole protein nasogastric feeds given to patients. Two weeks after the end of the study period cytotoxin-producing A. hydrophila was again isolated, this time from nasogastric suction apparatus. One environmental isolate of A. cuviue was found in a nasogastric feed. The other seven isolates came from the tap, drain or draining board of the kitchen in the unit which was used for the preparation of patient’s feeds. The only aeromonads recovered from patients were two isolates of A. cuviue. The first isolate was cultured from the throat swab of a patient after 24 h on the unit at the time of discharge. Ten days later screening swabs on re-admission were negative. A second patient had A. cuviue in perineal and rectal swabs 18 days after admission to the unit. The samples were taken 8 days after recovery of the first aeromonas isolate. Subsequent samples from this patient for the remainder of the study period were negative. No patient had diarrhoea solely attributable to aeromonas. The relationships of all isolates from the hospital are illustrated in Figure 1. No environmental strain was detected in any patient throughout the study. A total of 19 different strains of the three named species among 32 isolates were identified. In the intensive care unit the kitchen tap, drain or draining board yielded the same strain of A. cuviae on five occasions, plus two other strains. A feed had a further strain of A. cuviue. Both patient isolates of A. cuviae were distinguishable. Six A. hydrophila isolates in the hospital water supply and on the intensive care unit from intragastric feeds and nasogastric aspiration bottles were all identical. All isolates of A. sobriu were different.
spp. in a hospital
Aeromonas Specimens
sampled;
173
Waters i ITU
Faeces
I
I
t
Other
Aeromonos
M
J
J
A
.
sobria
.
.
MJJASONDJF
1982
1983 Calendar
1984
months
Strains of Aeromonus isolated from humans and the hospital environment. n , Human isolates; A, Water isolates; 0, Other environmental isolates. Each horizontal line represents isolates of a single strain.
Discussion
This study illustrates the level of colonization of patients and the environment in a hospital by Aeromonas spp. in the absence of any outbreak. No previous study of this kind has been done. It is notable that with the use of special isolation techniques aeromonads appear to be not uncommon. However, unlike some other gram-negative organisms (Cross, 1985) the isolation rate is not greatly increased by admission to hospital. As in previous studies of clusters of cases we have found considerable heterogeneity among the aeromonads isolated. The hospital is in an old building and it was impossible to establish with certainty the plumbing connections throughout the building. We have therefore assumed that, although some areas were mainly supplied by a particular tank, there were potential connections between all parts of the system and patients were at risk of acquiring any strain of aeromonas found in any part of the water system. The strains probably came from different
174
S. E. Millership
et al.
sources. Some may have been present in the water distribution system (Hazen et al., 1979; Burke et al., 1984; Stephenson et al., in press), other strains may have been introduced by contamination of the tank (Millership & Chattopadhyay, 1985) and yet others by local contamination of taps. The most striking finding from our study is the lack of relationship between water and human isolates. Also, if aeromonads were acquired from drinking water it might be expected that different patients would have indistinguishable isolates, but this is not the case. There is some evidence that A. caviae is non-pathogenic in the gut (Figura et al., 1986) whereas the species producing cytotoxin are likely to cause diarrhoea (Cumberbatch, et al., 1979; Millership, et al., in press). It is therefore surprising that toxigenic strains, which were administered to patients on gastric acid inhibitors by enteral feed, were not detected in faeces, nor was any change in the patient’s clinical condition observed. It therefore seems that the isolation of Aeromonas sp. from a water supply or the environment does not necessarily imply that there is a risk of diarrhoeal disease. It is likely that more than one virulence factor is involved in the production of gastroenteritis, as is often the case with other alimentary pathogens when acquired from drinking water or foods. References Abrams, E., Zierdt, C. H. & Brown, J. A. (1971). Observations on Aeromonas hydrophila septicaemia in a patient with leukaemia. Journal of Clinical Pathology 24, 491427. Agger, W. A., McCormick, J. D. & Gurwith, M. (1985). Clinical and microbiological features of Aeromonas hydrophila-associated diarrhoea. Journal of Clinical Microbiology
21,909-913. Barer, M. R., Millership, S. E. & Tabaqchali, S. (1986). Relationship of toxin production to species of the genus Aeromonas. Journal of Medical Microbiology 22, 3033310. Burke, V., Robinson, J., Gracey, M., Peterson, D. & Partridge, K. (1984). Isolation of Aeromonas hydrophilu from a metropolitan water supply: seasonal correlation with clinical isolates. Applied and Environmental Microbiology 48, 361-366. Cookson, B. D., Houang, E. T. & Lee, J. V. (1984). The use of a biotyping system to investigate an unusual clustering of bacteremias caused by Aeromonas species. Journal of Hospital Infection 5, 205-209. Cross, A. S. (1985). Evolving epidemiology of Pseudomonas aeruginosa infections. European Journal of Clinical Microbiology 44, 156-159. Cumberbatch, N., Gurwith, M. J., Langston, C., Sack, R. B. & Brunton, J. L. (1979). Cytotoxic enterotoxin produced by Aeromonas hydrophila: relationship of toxigenic isolates to diarrhoeal disease. Infection and Immunity 23, 829-837. Dice, L. R. (1945). Measures of the amount of ecologic association between species. Ecology 26, 297-302. S., Ceccherini, C. & Bereri, A. (1986). Prevalence, species Figura, N., Marri, L., Verdiani, differentiation and toxigenicity of Aeromonas strains in cases of childhood gastro-enteritis and in controls. Journal of Clinical Microbiology 23, 595-599. gastroenteritis. Lancet Gracey, M., Burke, V. & Robinson, J. (1982). A eromonas-associated
ii, 1304-l 306. von Graeventiz A. & Mensch, A. H. (1968). The genus Aeromonas in human bacteriology. Report of 30 cases and review of the literature. New EnglandJournal of Medicine 278, 245-249. Hazen, T. C., Fliermans, C. B., Hirsch, R. P. & Esch, G. (1978). Prevalence and distribution of Aeromonas hydrophila in the United States. Applied and Environmental Microbiology 36, 731-738.
Aeromonas
spp. in a hospital
175
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