Characteristics of aeromonas species and their association with human diarrhoeal disease.

Aeromonas species are members of the Vibrio722 without diarrhoea had Aeromonas isolated naceae family, like Vibrio cholerae. They are from their stool samples (13). Another study oxidase-positive, Gram-negative, facultative anaecarried out in the UK found 1.25% of stools robic rods, usually motile with polar flagella and positive for Aeromonas in symptomless subjects, can be differentiated biochemically from other 13.2% in patients with diarrhoea and other enteric genera of Vibrionaceae. pathogens and in 7.1% of patients with diarrhoea without other recognised pathogens (14). These Evidence implicating Aeromonas spp. as studies provide strong supportive evidence for human intestinal pathogens Aeromonas spp. having a pathogenic role in human diarrhoeal disease. In Thailand, isolations Aeromonas spp. were first implicated as a cause were relatively frequent whether subjects had of gastroenteritis in 1961 during an outbreak of diarrhoea (16.2%) or not (10%); this resembles diarrhoea in a nursery for neonates in Colombia (1 ). the situation with Campylobacter jejuni which is Subsequently, episodes of Aeromonas-associated often found in symptomless individuals in the diarrhoea have been reported from many countries tropics but not in industrialised societies (15). We including those in North America (2-4), Europe (5), have recently found Aeromonas spp. in the faeces India (6), Africa (7, 8), Australia (9), and Indoof 15.5% of Balinese children with diarrhoea nesia (10). Although Aeromonas spp. are recogand 12.7% of children without diarrhoea (16); nised as opportunistic pathogens in immunocomthis study is important in demonstrating that the promised hosts (11 ), their role as enteric pathogens isolation rate of strains producing cytotoxic entera is still considered by some to be "not proven" (12). toxin in children with diarrhoea (7.1 % ) was more Reported rates of isolation of faecal Aeromonas than twice that found in children in the control spp. vary a great deal (Table), probably because group (2.8%) and that most of the isolates were of differences in selection of patients for study, A. hydrophila, a strain associated with environ variations in laboratory methodology, and real mental sources, geographical differences in incidence of Aero monas-related intestinal infections. Other factors. Classification and identification such as age, have a significant influence on isolation rates too. The difficulties encountered in assessing the Few studies have compared isolation rates of potential pathogenic role of Aeromonas species Aeromonas in patients with and, without diarrhoea. relate to lack of agreement about their taxonomy In Perth, Australia, we found more than 10% of and classification. This aspect has been high 1156 children with diarrhoea but less than 1% of lighted in a paper by Popoff (17). Methods for a matched control group had enterotoxigenic isolation and identification of the organisms, also, Aeromonas spp. in their faeces (9). In Italy, 1.2% are not uniform. Our practice is to use layered of 495 children with diarrhoea and only 0.13% of blood agar plates with 10 ug/ml of ampicillin, a level below the usual inhibitory concentration for Correspondence and reprint requests should be most species (18). With this method, the raised, addressed to Dr. M. Gracey. greyish, rounded colonies of Aeromonas spp.