Aeromonas caviae, bacterie ubiquiste de l'environnement hydrique, emerge comme agent de diarrhees et dans des manifestations extra-intestinales. Son pouvoir pathogene a ete longtemps sous-estime et ses facteurs de virulence sont mal connus. Une serie de 28 cas cliniques d'infections a A. caviae majoritairement monomicrobiennes a ete observee dans les hopitaux de la region de Strasbourg durant une periode de quatre ans. Il s'agissait de huit enfants et 13 adultes diarrheiques, ainsi que de sept adultes bacteriemiques, la plupart immunodeprimes, avec un terrain favorisant, (affections cancereuses ou hepatobiliaires, gastrectomie, pH alcalin du tractus intestinal). Nous avons observe une adherence aux cellules HEp-2 et la presence de flagelles lateraux pour des souches d'A. caviae isolees de diarrhees. L'activite hemolytique a ete recherchee sur gelose au sang de mouton et le titre hemolytique a ete determine sur des suspensions d'erythrocytes de lapin. Nous avons montre la presence d'une aerolysine chez une souche d'A. caviae isolee d'une bacteriemie, confirmee par l'amplification du gene codant l'aerolysine. In vitro cette toxine necessitait une activation par la furine pour produire un effet hemolytique. De meme l'ajout de la furine permettait de mettre en evidence une activite enterotoxique par l'accumulation de liquide dans les anses ileales isolees de lapin. A. caviae est ainsi un pathogene dont la survie est favorisee par l'immunodepression, les affections cancereuses et hepatobiliaires, et un pH intestinal legerement alcalin. Ses capacites d'entero-adherence permettent la colonisation et la production d'aerolysine se traduit par son enterotoxicite.
Aeromonas caviae, an ubiquitous aquatic organism, has long been considered to be of low pathogenicity, and its virulence mechanisms are still not clearly understood. Twenty-eight A. caviae isolates of clinical origin, most often monomicrobic, were identified in our university hospital over a four year period. Patients, mostly immunocompromised, were: eight diarrhoeal infants, 13 diarrhoeal adults, seven bacteraemic adults. Adults were frequently suffering from underlying intestinal malignancy, hepatobiliary disease, gastrectomy. Virulence factors were investigated. Adherence, studied by use of tissue culture HEp-2 cells, and staining of characteristic lateral flagella, were observed in diarrhoeal strains. Extracellular hemolytic activity was tested on rabbit erythrocytes suspensions at 25 and 37 o C. One blood culture isolate showed an important hemolytic activity at 25 o C, but none at 37 o C. Treatment with furin activated the aerolysin precursor and resulted in significant hemolysis at 37 o C, and fluid accumulation in rabbit ileal loops similar to that of A. hydrophila as control. The presence of the hemolysin gene was confirmed in this strain by PCR. In conclusion, A. caviae was shown to be a pathogen isolated from diarrhoea and bacteraemia in immunocompromised patients with malignancies and low gastric acidity as favouring factors. Virulence including the ability to adhere to cells and the production of lateral flagella was observed in diarrhoeal strains. The expression and the production of extracellular hemolytic activity and enterotoxicity at 37 o C depended on the activation of the pore forming toxin aerolysin precursor by furin. In vivo the protoxin is probably processed to its mature form by host proteases.