Virulence profiles and other biological characters in water isolated Aeromonas hydrophila

Thirty water isolates of A. hydrophila were tested for potential virulence profiles, antibiotic resistance and Bacteriocin-Like Substances (BLS) produ ction. Cytotoxic activity was present in all strains tested, 87% were hemol ytic and 70% adhesive. Lysine decarboxylase reactions (LDC) positivity was correlated with virulence factors: 100% versus cytotoxicity, 84% versus adh erence, 76% versus hemolytic activity. The correlation was also present in the LDC-negative strains. Hemolytic and cytotoxic activities were frequentl y associated: high cytotoxicity, corresponding to high hemolytic activity a nd vice versa. The in vitro susceptibility of A. hydrophila to 28 antibacte rial agents showed that cefotaxime was the most active beta -lactam antibio tic, and Cefuroxime inhibited 90% of the strains. Isolates were resistant t o Penicillin G, Ampicillin, Carbenicillin, Amoxicillin, Cephalotin and Cefa clor. Tetracycline, Chloramphenicol, Nitrofurantoine, the quinolones and th e aminoglycosides (except Streptomycin) were consistently active. BLS produ ction never emerged against closely-related microorganisms, On the contrary A. hydrophila presented a heteroinhibitory activity against non-taxonomica lly related genera such as Listeria spp. (L. seeligeri NCTC 11856, L. welsh imeri NCTC 11857, L. ivanovii NCTC 11846) and S aureus ATCC 25923. Although a large number of strains showed virulence determinants together with othe r biological characters such as antibiotic resistance and BLS production, i t was not possible to relate these factors to the observed plasmids.