Evaluation of Antimicrobial Susceptibility Pattern Changes and Antibiotic Resistance Genes of Vibrio cholerae O1 Strains Isolated in 2012-2015 Outbreaks in Iran Referred to Reference Laboratory Using Phenotypic and Molecular Methods

Background & objectives: Antibiotic resistance in Vibrio cholerae is a crucial matter in the world. Objective of this study was the improvement of cholera surveillance by assessing the antimicrobial resistance pattern and bacterial resistance genes in V. cholerae O1 isolates, reffered to Iranian Reference Health Laboratory, in cholera outbreaks during 2012- 2015. Methods: This study is a cross sectional- descriptive research. Antimicrobial susceptibility test (AST) to 8 antibiotics was performed on 113 V.cholerae O1 isolates using E-test method. For all isolates, conventional PCR method was used to detect the presence of tetracycline resistance genes (tetA, tetB and tetC) and the sulfamethoxazole-trimethoprim resistance genes (sul2 and dfrA1). Results: All isolates were sensitive to ampicillin, temocillin, ciprofloxacin and cefixime and 64% of strains showed intermediate susceptibility to erythromycin. The resistance rate of nalidixic acid, sulfamethoxazole-trimethoprim and tetracycline were 90%, 71% and 50% respectively. However, the frequency of multidrug resistant (MDR) strains varied across the years. The frequency of resistance genes (tetA, tetB, tetC, sul2 and dfrA1) were 70%, 34%, 58%, 66% and 70% respectively. Conclusion: AST should be used to determine the resistance profile at the beginning of a cholera outbreak and to monitor the resistance profile of circulating strains as part of surveillance of the disease. A prominent association was observed between phenotypic resistance to sulfamethoxazole-trimethoprim and presence of dfrA1gene. Determining the presence of resistance genes is necessary for understanding the epidemiology and routes of transmission of antibiotic resistance genes