Molecular Epidemiology of Colonizing Methicillin-Resistant Staphylococcus aureusin Patients Admitted to Teaching Hospital, Karapitiya

Abstract

Methicillin-resistant Staphylococcus aureus (MRSA) is a pervasive multi-drug resistant pathogen. Acquisition ofresistant genes and virulence mechanisms have become the major concerns. Microbiological identification gives an adquate insight regarding these mechanisms. Robust identification is required for planning an effective antimicrobial therapy against the pathogen. The study was aimed to describe the molecular epidemiology of MRSA isolates collected from the Teaching Hospital, Karapitiya. Patients were enrolled from orthopaedic, medical and surgical wards for six months from September 2016. Nasal swabs were collected from anterior nares within 24 hours of admission and 48 hours prior to discharge. MRSA isolates were identified based on cefoxitin resistance as in Clinical and Laboratory Standard Institute guidelines. Identification of mecA, femB and Panton-Valentine Leucocidin (PVL) genes and Staphylococcal Cassette Chromosome mec (SCCmec) types were performed using polymerase chain reaction. A total of 502 patients were enrolled on admission. Of them, discharge samples were collected from 360 patients. Patients colonized with MRSA on admission and at discharge were 31 (6.2%) and 24 (6.7%), respectively. All 55 isolates were positive for mecA. Of those, 7 (22.5%) and 6 (25%) isolates were positive for PVL and 30 (96.7%) and 23 (95.8%) isolates were positive for femB. SCCmec typing indicated SCCmec type IV (18, 58%), V (3, 9.6%), I (3, 9.6%) and III (7, 22.5%) on admission and SCCmec type IV (16, 67%), V (3, 12.5%) and III (2, 8.3%) including three none-typable isolates at discharge. Molecular profiles confirmed that all MRSA isolates were positive for mecA. Around one-fourth of them were positive for PVL. More than half of the isolates carried SCCmec type IV and V. Isolates positive for PVL gene carrying SCCmec type IV and V may cause more virulent infections compared to the others. Molecular epidemiology provides a better insight for planning effective antibiotic therapy.