antibiotic resistance pattern among gram negative mercury resistant bacteria isolated from contaminated environments

background mercury is one of the most toxic heavy metals. even a small amount of it is toxic for all living organisms. some of bacteria have developed special resistance mechanisms against mercury, in addition to resistant to different antibiotics. these bacteria usually acquire hg and antibiotic resistance genes via horizontal gene transfer in their habitat. objectives the aim of this study was isolation and identification of mercury resistant bacteria and evaluating the relation between increase of environmental levels of mercury and prevalence of antibiotic resistance among gram negative hg resistant bacteria. materials and methods the samples were collected from water and sediments of kor river. we evaluated amounts of mercury in the water and sediment samples and counted the number of bacteria in both hg containing and non-hg containing media. antibiotic resistance pattern was studied using disk diffusion method for hg resistant and hg sensitive bacteria. results the frequencies of mercury resistant bacteria were between 35% for pole khan station and 2.5% for doroodzan station. these stations were the most and the lowest mercury-contaminated areas of the kor river respectively. pseudomonas sp., entrobacter sp., escherichia coli, klebsiella sp. and serratia marcescens were isolated as mercury resistant bacteria. the highest level of antibiotic resistance was seen for ampicillin, tetracycline and sterptomycin. antibiotic resistance frequencies among these bacteria were higher than mercury sensitive ones. conclusions our results showed that hg resistance genes in contaminated areas are exchanged between residing bacteria along with the antibiotic resistance genes and resulted in prevalence of antibiotic resistance among residing bacteria.