INFLUENCE OF SALT CONCENTRATION ON THE SUSCEPTIBILITY OF MODERATELY HALOPHILIC BACTERIA TO ANTIMICROBIALS AND ITS POTENTIAL USE FOR GENETICTRANSFER STUDIES

The influence of salinity on the susceptibility of 13 moderately halop hilic collection strains belonging to the genera Chromohalobacter, Del eya, Halomonas, Vibrio, and Volcaniella to 10 common antimicrobials ha s been studied. Three different patterns of tolerance were found when salinity was varied from 10 to 1% (wt/vol) total salts in the testing media. The first one included the responses to ampicillin and rifampic in, where only minimal effects on the susceptibility were found. All m oderate halophiles showed a high sensitivity to rifampicin regardless of the salt concentration. In the second group, including the response s to the aminoglycosides gentamycin, kanamycin, neomycin, and streptom ycin, a remarkable and gradual increase of the toxicity was detected a t lower salinities. Thirdly, the highest heterogeneity was found for t he rest of antimicrobials assayed (trimethoprim, nalidixic acid, spect inomycin, and tetracycline), where the effect of salinity was moderate and dependent on both the individual strain and the antimicrobial tes ted. The data presented here should facilitate genetic studies on mode rate halophiles. Thus, they simplify the design of selection media for genetic exchange experiments. Besides, by using low-salinity media, g enes encoding resistance to a number of antimicrobials, especially to aminoglycosides, can be used as genetic markers for plasmids or transp osons to be transferred to these extremophiles.