Molecular characterization of Staphylococcus aureus strains isolated from hospitalized patients based on coagulase gene polymorphism analysis: High frequency of vancomycin-intermediate S. aureus and the emergence of coagulase type II in Iran

Abstract

Staphylococcus aureus is a leading cause of nosocomial infections and a significant contributor to economic and societal cost. There has been a worldwide increase in infections related to S. aureus especially with those expressing a multi-drug resistance that makes the management of the infections difficult. In the current study, it is aimed to investigate the coa gene polymorphism, prevalence, resistance and virulence pattern in S. aureus strains. A total of Ninety-five clinical S. aureus strains were investigated in the study. Antibiogram analysis was done by disk diffusion test method except for vancomycin and mupirocin (broth microdilution). Methicillin resistance was determined by using the cefoxitin disk diffusion test and subsequently PCR of the mecA gene was done. Inducible resistance to clindamycin was identified by D-test. The genetic background was characterized by coagulase typing. The overall prevalence of methicillin-resistant S. aureus (MRSA) and methicillin-susceptible S. aureus (MSSA) was 67.4% and 32.6%, respectively. The multidrug resistance (MDR) rate for MRSA isolates was higher than MSSA (87.5% vs 77.4%). Intermediate resistance to vancomycin in S. aureus (VISA) was detected in 11.6% of strains which all were MRSA and isolated from intensive care unit (ICU). Resistance to mupirocin was confirmed in 30.5% of strains which of these 34.5% and 65.5% exhibited resistance to mupirocin in high and low level respectively. The overall prevalence of cMLSB, iMLSB, and MS phenotype was 45.3%, 23.2%, and 3.1% respectively. Both iMLSB and cMLSB phenotypes predominated in MRSA strains. A total of seven coa type were found in this study. coa type II was the most prevalent type (44.2%). Isolates of coa type II had higher detection of pvl and tst genes than those of other types identified. The MRSA-coa II expressed the greatest MDR while coa IVb and VIII were susceptible to all applied antibiotics. Present data revealed that spreading seven coa types of S. aureus with a high prevalence of VISA strains which is a serious threat in our region. Our study supported careful monitoring of vancomycin treatment to prevent the further spread of VISA and VRSA strains.