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Five Aeromonas strains, isolated from both clinical and environmental sources and characterized by a polyphasic approach, including phylogenetic analysis derived from gyrB, rpoD, and 16S rRNA gene sequencing, as well as DNA-DNA hybridization, extensive biochemical and antibiotic susceptibility tests, were recognized as members of an unknown, or undescribed, Aeromonas species. These "Aeromonas eucrenophila-like" strains were closely related to the species A. eucrenophila and Aeromonas encheleia, but they were negative for indole and acid from glycerol tests. Therefore, based on the results of the phylogenetic analyses and DNA-DNA pairing data of these strains, a novel species of the genus Aeromonas is described, for which the name Aeromonas tecta is proposed with isolate F518(T) (CECT7082(T), DSM17300(T), MDC91(T)) as the type strain.

Two Aeromonas strains, IBS S6874(T) and IBS S6652, were isolated from the faeces of two healthy monkeys (Macaca fascicularis) from Mauritius that were kept in quarantine in the Centre for Primatology, Strasbourg, France. Phylogenetic analysis based on 16S rRNA gene sequences showed that the two isolates formed an unknown genetic lineage within the genus Aeromonas. The two isolates had nearly identical sequences (0.1 % nucleotide substitution) that were related closely to those of recognized Aeromonas species (1.7-3.5 % nucleotide substitution). DNA-DNA hybridization showed that strains IBS S6874(T) and IBS S6652 had high DNA-DNA similarity (89 %) to each other and a low level of DNA-DNA similarity to closely related taxa (18 % relatedness to Aeromonas trota and 16 % relatedness to Aeromonas schubertii). Phenotypically, the two monkey isolates differed from most previously described mesophilic Aeromonas species by their lack of haemolysis on sheep-blood agar and inability to produce indole, gas from glucose or acid from mannitol. They differed from the most closely related species, A. schubertii, by their ability to produce acid from D-cellobiose and D-sucrose and by their pyrazinamidase activity. The name Aeromonas simiae sp. nov. is proposed for these isolates; strain IBS S6874(T) (=CIP 107798(T)=CCUG 47378(T)) is the type strain.

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 degrees C. One blood culture isolate showed an important hemolytic activity at 25 degrees C, but none at 37 degrees C. Treatment with furin activated the aerolysin precursor and resulted in significant hemolysis at 37 degrees 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 degrees 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.