Soap Lake, located in Washington State, is a meromictic, soda lake. Many bacterial isolates retrieved from Soap Lake have been noted to possess resistance to multiple antibiotics. A likely explanation for the wide range of antibacterial resistance exhibited by these strains is due to the impact of high alkalinity on the antibiotics themselves and not due to the presence of antibiotic resistance genes. The aim of our study was to determine if select antibiotics are effective against Halomonas eurialkalitoleranis, a bacterium capable of growth over a wide range of neutral to alkaline pH values, to investigate the influence of alkalinity on antibiotic activity. Five strains of Halomonas eurialkalitoleranis were isolated from Soap Lake sediment. Halomonas eurialkalitoleranis Isolate 9 was inoculated into media buffered over a range of pH values, 7-11. Select antibiotics; tetracycline, ampicillin, vancomycin, neomycin trisulfate salt, demeclocycline, sulfamethizole, kanamycin, chloramphenicol, streptomycin, roxithromycin, erythromycin, and sulfamethaxole, were suspended in inoculated media, to determine their minimum inhibitory concentration (MIC) over the range of pH values tested. Tetracycline, ampicillin, kanamycin, neomycin, roxithromycin, and streptomycin, were found to become ineffective against Isolate 9 at pH values above 8. Vancomycin did not produce statistical differences in MIC values at any pH tested. Erythromycin and sulfamethizole were found to be more effective against Isolate 9 at pH 11 than in neutral media. In addition, polymerase chain reactions were performed to determine if Isolate 9 possessed known genes for antibiotic resistance against the twelve antibiotics tested. Isolate 9 was found to possess resistance genes for all antibiotics tested, except kanamycin and streptomycin. --Abstract, page iv
