Rattus norvegicus: not a model for Aeromonas-associated gastroenteritis in man

The lack of a suitable animal model of Aeromonas-associated diarrhoea has hampered investigations into Aeromonas pathogenic mechanisms. Hence, a published report that clindamycin-pretreated rats developed signs and symptoms of enteritis following intragastric inoculation of an Aeromonas strain required further investigation. Although we could demonstrate long-term colonisation (>12 days) and histological damage in this animal model with Pseudomonas aeruginosa isolated from patients with chronic diarrhoea, this was not seen with Aeromonas spp. Six Aeromonas strains, selected for their potential virulence and colonising abilities and including the strain from the original report, were either not recovered from stools or were recovered for no longer than 2 days post inoculation. Intestinal histology remained normal. Destruction of bacteria in vivo appeared to be due to immune mechanisms as inoculum strains were not 'suicidal' or unduly sensitive to low pH or clindamycin. This study was, therefore, unable to validate the clindamycin-treated rat model as a useful one for investigating the enteropathogenicity of Aeromonas species. Possible reasons for the discrepancy between our study and the original report are discussed.