Molecular characterization of staphylococcal cassette chromosome MEC in methicillin-resistant staphylococci -

Abstract

Background: Methicillin-resistant staphylococci (MRS) are major human pathogens accounting for most hospital-acquired (HA) infections across the world. More recently community-acquired (CA) MRS strains have emerged. These CA-MRS strains differ from HA-MRS strains in that they are susceptible to a wider range of antimicrobial agents and possess a staphylococcal cassette chromosome mec (SCCmec) type IV or V. The recent increase of methicillin resistance among staphylococci led us to investigate the genotypes of the MRS strains that could be circulating. Therefore, this study aimed at determining the antimicrobial agents profiles, SCCmec types, genotypes, and prevalence of Panton-Valentine leucociden (PVL) and toxic shock syndrome toxin 1 (TSST-1) among the studied MRS isolates.Methods: Thirty-six MRS isolates collected between October 2010 and September 2011 at Clemenceau Medical Center (CMC), Lebanon were typed using various phenotypic and genotypic methods. Antimicrobial susceptibility was determined using the disk diffusion agar method. SCCmec typing was performed by multiplex PCR and sequence analysis. The prevalence of the genes encoding PVL and TSST-1 virulence factors and their transcription levels, were determined by quantitative real-time PCR. The genomic relatedness of the isolates was assessed by random amplified polymorphic DNA (RAPD) analysis. Results: Antimicrobial susceptibility determination revealed three distinct antibiotypes. The predominant SCCmec type found among the MRS isolates was type IVa (51percent). Twenty-nine percent harbored SCCmec type III and 14percent harbored SCCmec type II. Only one isolate harbored SCCmec type IVc, and one harbored SCCmec type I. All methicillin-resisrtant Staphylococcus aureus (MRSA) isolates were negative for the gene encoding for PVL, and two were positive for the gene encoding for TSST-1. RAPD analysis demonstrated high genomic diversity among the MRS isolates.Conclusion: This study demonstrated the SCCmec types and the clonality of the MRS strains, allowing the diffe