Bacteriocin-like substance of Aeromonas hydrophila.

The genus Aeromonas comprises Gram negative rods found mainly in aquatical environments that may infect humans and animals (JM Janda 1991 Clin Microbiol Rev 4: 397-410). In humans, some Aeromonas species have been associated with intestinal and extraintestinal infections and enterotoxins, cytotoxins as well as invasive mechanisms have been incriminated in the development of illness in the host (Janda loc. cit.). Bacteriocin-like substances (BLS) are protein compounds produced by some bacteria (G Ivanovics 1962 Bacteriol Rev 26: 108-118) showing antagonic activity against their own species (isoinhibitory activity IA) or other non-related species (heteroinhibitory activity HA). The use of the expression BLS is recommended to nominate bacterial products showing antagonic activity though not characterized (K Sandhu et al. 1983 J Clin Microbiol 17: 511-515). These substances have been widespread utilized in epidemiological studies as specific marker properties of bacteria, in the regulation of population dynamics in bacterial ecosystems and clinical treatment (V Fantinato & F Zelante 1991 Rev Microbiol 22: 49-51). As BLS have not been currently described in Aeromonas species, the purpose of this study was to investigate their production in strains isolated from animal, clinical and environmental sources. The assays for the production of BLS were performed according to Sandhu et al. (loc. cit.). The strains used as BLS producers and BLS indicators are listed in Table. Our results showed that among 32 Aeromonas strains, the BLS could be only demonstrated in a strain of A. hydrophila isolated from a water tank containing alligators. This strain demonstrated heteroinhibitory activity against four Staphylococcus aureus strains (one ATCC 6538 and three methicillin-resistant MRSA). The heteroinhibitory activity was demonstrated after an incubation of 48 hr at 37°C and not at 25°C, conditions also observed for the BLS production in Serratia, Pseudomonas, Leuconostoc and Enterococcus strains (JD Foulds & D Shemin 1969 J Bacteriol 99: 655-660, JRW Govan & G Harris 1985 J Clin Microbiol 22: 490-494, F Mathleu et al. 1993 J Appl Bacteriol 74: 372-379, F Villani 1993 J Appl Bacteriol 74: 380-387). The heteroinhibitory activity was demonstrated by inhibitory zones ranging from 17 to 27mm. JR Govan (1986 Scand J Infec Dis 49: 31-37) proposed that different inhibition zone diameters may depend on the potency either of BLS action or they may be correlated with the number of receptors for BLS in the bacterial surface. In spite of these results, further research is necessary to better understand the bacteriocin-like activity in Aeromonas species as well as to investigate the chemical nature of this substance and its pharmacological usefulness.