SCC mec type and Antimicrobial susceptibility pattern of MRSA Isolated from blood stream infection in Phramongkutklao hospital

Abstract

Methicillin-resistant Staphylococcus aureus (MRSA) is a major cause of infection in hospitals. The main mechanism of antibiotic resistance is mediated by producing an altered penicillin-binding protein (PBP2a), which has low affinity to beta-lactams drug. This protein is encoded by mecA gene, located on Staphylococcal Cassette Chromosome mec (SCCmec).  Nowadays, at least 11 types of SCCmec elements have been identified using multiplex PCR. The objectives of this study were to identify and characterize the SCCmec type and evaluate the antibiotic susceptibility pattern of MRSA isolated from blood. A total of 124 MRSA isolates were collected from blood samples of bloodstream infection in Phramongkutklao hospital from January 2012 to December 2013. All the isolates were identified as MRSA by agar oxacillin and mecA-mediated oxacillin resistance method. The genotyping study demonstrated that all MRSA isolates were positive for 16SrRNA gene and mecA gene. SCCmec typing showed 74 (59.7 %) of isolates were SCCmec type I, 41 (33.1 %) of isolates were SCCmec type II, 4 (3.2 %) of isolates were SCCmec type III, 3 (2.4 %) of isolates were SCCmec type IV and 2 (1.6 %) of isolates were untypable. Their antibiotic susceptibility was performed using disk diffusion method for nine antimicrobial agents, including ciprofloxacin, levofloxacin, erythromycin, clindamycin, gentamicin, fosfomycin, fusidic acid, tetracycline and trimethoprim/ sulfamethoxazole. The result showed that 100%, 94.4%, 66.7%, 64.8%, and 10.5% of the MRSA strains were susceptible to fusidic acid, trimethoprim/sulfamethoxazole, fosfomycin, tetracycline, and gentamicin respectively. The MIC of vancomycin, by E-tests, ranged from 0.5 to 2 µg/mL. They were also arranged in 10 Antibiograms, of which pattern 1 (susceptible to vancomycin, fusidic acid, trimethoprim /sulfamethoxazole, fosfomycin and tetracycline) and 3 (susceptible to vancomycin, fusidic acid and trimethoprim/sulfamethoxazole) were mostly found with frequency of 52.4 % and 28.2 %, และ respectively.