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Influence of NaCl Salt Concentration on the Susceptibility of Moderately Halophilic Bacteria to Antibiotics

Antibiotics are extensively used as selective agents in genetic exchange experiments. In the case of moderate halophiles, it has been reported that when they are grown at their optimal salt concentration,(usually about 10%) they tolerate very high concentrations of the majority of the antibiotics. The susceptibility of some of moderately halophilic collection strains belonging to different genera to some common antibiotics has been investigated and effect of NaCl salt different concentrations(0%, 5%, 10%, and 15%) on the operation of mentioned antibiotics has been studied. Antibiotic sensitivity was tested by Kirby-Bauerʹs disk diffusion method on Muller Hinton Agar medium(M.H.A). Zone of inhibition was measured and sensitivity was determined against standard inhibition zones. Three different patterns of tolerance to Antibiotics were found when salt concentration(NaCl) was varied in the testing media. The first one included the responses to erythromycin, vancomycin, where only minimal effects on the susceptibility were found or was not seen any effect. In the second group, including the responses to gentamycin, amikacin, a remarkable and gradual increase of toxicity was detected at lower salinities. Thirdly, the highest heterogeneity was found for the rest of antimicrobials assayed, where the effect of salinity was moderate dependent on both the individual strain and the antibiotic tested. The data presented here should facilitate genetic studies on moderate halophiles and design of selection media for genetic exchange experiments. Otherwise, identification of resisting halophilic bacteria that disperse in environment is very important because of genetic transformation of resistance gene to pathogen bacteria.