Phenotypic and Genotypic study of vancomycin resistance inMethicillin-ResistantStaphylococcus aureus (MRSA) isolates collected from clinical specimens at Imam Reza and SinaHospitals of Tabriz.

Background: Methicillin-resistant Staphylococcus aureusis an important cause of severe infections in hospital and community and infections caused by this strains can lead to high mortality. Typing of SCCmec, in addition to separating strains associated with community and hospital. Staphylococcus aureus with reduced susceptibility to vancomycin (hVISA, VISA, VRSA), associated with high mortality rate and started to increase in the world, so, the use of genetic markers that identify vancomycin MIC in a short time in a MRSA epidemic is a necessity. Methods: By using several phenotypic tests such as Gram stain, catalase, coagulase, DNase and manitol fermentations and by screening resistance to methicillin, 100 MRSA isolates were identified. For identifying resistance to vancomycin, phenotypic tests with the disc diffusion method, determining MIC byE-test method and screening test in BHIA (Brain Heart Infusion Agar) containing vancomycin and molecular PCR test in order to identify femB, mecA, vanA,SCCmecI, II, III, IVa, IVb, IVc, IVd and Vgenes were carried out. Results: In the E-test method 92% VSSA and 8% hVISA were identified. However, screening tests in BHIA, containing3 μg/ml and4 μg/ml vancomycin, detected 18% hVISA and 4% VISA, respectively. Frequency of types and sub-types found were as follows: SCC mecIII (77%), SCCmecI (5%), SCCmecIVa (1%), SCCmecIVc (1%), mixed strain SCCmecIVc-III (1%) and strains Non typeable (15%). the Kruskal-Wallis test indicate a significant association in SCCmecIII and Non type able isolates with high vancomycin MIC (MIC 2 μg /ml) (p=0.015). Conclusion: In our study, the isolates with SCC mecIII type were associated with high vancomycin MIC. Among the variety of types, SCCmecIIIcould be considered as a genetic marker of organism for surveillance in healthcare settings.

کلیدواژه ها:

Methicillin-resistant Staphylococcus aureus ، E-test ، vanA gene ، Vancomycin agar screening ، SCCmec ، Multiplex-PCR