DISTRIBUTION OF CPHA OR RELATED CARBAPENEMASE-ENCODING GENES AND PRODUCTION OF CARBAPENEMASE ACTIVITY IN MEMBERS OF THE GENUS AEROMONAS

The prevalence of the cphA gene or related carbapenemase-encoding gene s was investigated in 114 Aeromonas strains belonging to the six speci es of major clinical interest. A species-related distribution of cphA- related sequences was observed. Similar sequences were found in A. hyd rophila, A. veronii by. sobria, A. veronii by. veronii, and A. jandaei , but not in A. caviae, A. trota, or A. schubertii. However, a single A. caviae strain (of 62 tested) was found carrying cphA-related sequen ces, suggesting the possibility of the horizontal transfer of this gen e to species which normally do not carry it, Production of carbapenema se activity was detectable in 83% of the hybridization-positive strain s but in none of the hybridization-negative ones. When it was present, carbapenemase activity was always inhibitable by EDTA. Either carbape nemase-producing or not, Aeromonas strains appeared to be susceptible to imipenem when in vitro susceptibility testing was performed,vith in ocula of conventional size (10(5) CFU), for which MICs were always les s than or equal to 1 mu g/ml. With a larger inoculum (10(8) CFU), the MICs for carbapenemase-negative strains always remained less than or e qual to 1 mu g/ml, while those for carbapenemase-producing strains wer e always greater than or equal to 4 mu g/ml, being usually higher than the breakpoint for susceptibility, The present results indicate that the production of metallocarbapenemase activity, apparently encoded by cphA homologs, is widespread among some of the Aeromonas species of c linical interest (A. hydrophila, A. veronii by. sobria, A. veronii by. veronii, and A. jandaei) and that imipenem MICs for carbapenemase-pro ducing strains are subjected to a relevant inoculum size effect.