Phenotypic and Genotypic Analysis of Gentamicin, Penicillin, Methicillin, Vancomycin, Linezolid and Tetracycline Resistance in Clinical Isolates of Staphylococcus aureus

Abstract

In this study, it was aimed to investigate the resistance rates of gentamicin, penicillin, methicillin, vancomycin, linezolid and tetracycline by phenotypic and genotypic methods in Staphylococcus aureus isolates and to determine plasmid content. Between the months of January and September in 2015, 100 clinical isolates of S. aureus were obtained from different samples such as wound, blood, urine. The automated bacteria identification and antibiotic susceptibility system (BD PhoenixTM, Sparks, MD, USA) was used to determine of antibiotic sensitivities. The resistance to methicillin was also investigated by Kirby-Bauer disc diffusion method using a 30 μg cefoxitin disc. The presence of aac(6’)/aph(2’’), blaZ, mecA, femA, vanA, vanB, cfr, tetK and tetM genes related to antibiotic resistance was investigated by PCR amplification in all isolates. Plasmid DNAs were isolated by using a Thermo Scientific GeneJET Plasmid Miniprep Kit. The cefoxitin resistance of S.aureus isolates, identified according to the results of disk diffusion and automated system, was calculated as 19%. Vancomycin and linezolid resistance were not observed in isolates while gentamicin 2%, penicillin 100%, methicillin 19%, tetracycline 18% resistance were identified using the automated system. According to the results of molecular analysis aac(6’)/aph(2’’), blaZ, mecA, femA, tetK and tetM genes frequencies were determined as 2%, 100%, 19%, 100%, 17% and 3% respectively, but vanA, vanB and cfr genes were not amplified by PCR. In order to determine the relationship between antibiotic resistance and plasmid presence, plasmids were isolated from identified bacterial isolates. It is found that most of bacterial isolates (79%) contain different numbers plasmids. Rapid and reliable method for antibiotic susceptibility is important to determine the appropriate therapy decision. PCR can be used for confirmation of the results obtained by automated system or could be used as an alternative diagnostic method in the routine diagnosis for rapid, sensitive, and specific detection of MRSA associated antibiotic resistance genes.