Molecular Characterization, Drug Resistance and Virulence Analysis of Constitutive and Inducible Clindamycin Resistance Staphylococcus aureus Strains Recovered from Clinical Samples, Tehran - Iran.

Background: Macrolide-lincosamide streptogramin B family is one of the important alternative antibiotics for treating staphylococcal infections. The aim of this study was to determine the characteristics and prevalence of antibiotic resistance genes in different coagulase types of clinical Staphylococcus aureus strains.

Methods: In the present study, 86 isolates with different phenotypes of MLSB resistance were investigated. In vitro susceptibility was assessed by the disk diffusion and broth microdilution methods. PCR assays were used to detect resistance-related genes. Coagulase and SCC mec types were identified by multiplex PCR assay.

Results: The prevalences of constitutive MLSB , inducible MLSB , and MS phenotypes were found to be 23%, 14.2%, and 4.9%, respectively. The rates of resistance to mupirocin, fusidic acid, and tigecycline were found to be 9.3%, 4.6%, and 2.3%, respectively. The top three predominant resistance genes were mecA, tet (M), erm (C) representing 75.6, 50, and 40.7% of isolates. mupA (7%), fusB (3.5%), and fusC (1.2%) genes were also detected among tested isolates. Coagulase types were mainly type II (34.9%), followed by III (32.6%), V (20.9%), and I (11.6%).

Conclusion: These findings indicated high resistance rate and low genetic variability with the prominence of coa type II, highlighting the particular importance of diagnosis of these strains to avoid treatment failure.