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Fresh and salt water samples analyzed in Rio de Janeiro city showed the presence of Plesiomonas shigelloides. Forty-six strains were isolated from both environments. A high incidence of P. shigelloides was achieved in polluted fresh and salt waters as well as in samples from non-polluted streams. P. shigelloides isolates had biochemical characteristics similar to those already described in the literature. None of the isolates analyzed produced enterotoxin in the suckling mouse assay. Hemolytic activity against sheep and human type A erythrocytes was detected in the strains tested. The results of the antibiotic susceptibility tests indicated that all the isolates were susceptible to the cephalosporins, penicillins combined with a beta-lactamase inhibitor, aminoglycosides, imipenem, norfloxacin, tetracycline, chloramphenicol and trimethoprim-sulfamethoxazole. All the isolates were resistant to the penicillins.

The Aeromonas genus have been consideredas important infectious agents in humans and ani-mals (JM Janda 1991 Clin Microbiol Reviews 4:397-410). The biological characteristics such as,toxins production (e. g. hemolysins, cytotoxins andenterotoxins) and also cell-associated features, thatappear to play important role in infectious pro-cesses in humans and animals, have been studiedin the attempt of elucidate patogenicity of the dif-ferent Aeromonas species (Janda loc. cit.). Evi-dences indicate that the animal passage may influ-ence in the expression of biological characteris-tics in many organisms such as, Plesiomonasshigelloides (SC Sanyal et al. 1980 J Med Microbiol13: 401-409) and Vibrio cholera O1 biotype ElTor (A Tikoo et al. 1994 J Med Microbiol 40: 246-251). DV Singh and SC Sanyal (1992 J MedMicrobiol 37: 262-267) reported that passagethrough rabbit instestines may control the expres-sion of the genes responsible for toxins produc-tion in Aeromonas spp.In this communication we report on the alter-ation of the hemolytic and enterotoxigenic charac-ter and also surface characteristics in one strain ofAeromonas isolated from environment, after ani-mal passage by endovenous route.Four samples of Aeromonas were used in thisstudy, three from polluted estuary water ( A. caviae- 030, Aeromonas sp. - 057, A. trota - 058) and onefrom drain treatment station supplyed by FundacaoOswaldo Cruz, Rio de Janeiro (A. hydrophila -T336). Those strains were maintend in nutrient agar(NA) with 1% of NaCl (FW Hickman-Brenner etal. 1987 J Clin Microbiol 25: 900- 906) at roomtemperature.All samples were tested with regar to hemol-ysin production, through β hemolysis zones aroundthe colonies in rabbit blood agar with 5% (v/v) oferitrocytes and the haemolitic activity was analyzedwith the metodology described by M Cumberbatchet al. (1979 Infect Immun 23: 829-837). The suck-ling mouse test (WA Dean et al. 1972 Infect Dis125: 407), was used for enterotoxin detection, theautoagglutination capacity for self pelleting (SP)and for preciptation after boiling (PAB) as de-scribed by JM Janda et al. (1987 Infect Immun 55:3070-77). The hidrofobic profile by phase parti-tioning with hydrocarbon solvents described by MRosenburg et al. (1980 Fems Microbiol Lett 9: 29-33).Strains for animal experiments were cultivatedin 5ml of BHI (OXOID) at 28