A ten year study of prevalence, antimicrobial susceptibility pattern, and genotypic characterization of Methicillin resistant Staphylococcus aureus causing ocular infections in a tertiary eye care hospital in South India

Abstract

Methicillin-resistant Staphylococcus aureus (MRSA) is an important cause of vision threatening ocular infections. This study aimed to determine the prevalence and antimicrobial susceptibility pattern of MRSA and their genotypic characterization in ocular infections. The study period was from January 2007 to December 2017 in Aravind Eye Hospital, Madurai. Retrospective analysis of clinical records found a total of 1306 Staphylococcus aureus in various ocular infections. Among these, 274 (21%) were found to be MRSA with an increased incidence from 9% in 2007 to 38% in 2017 (P = .007). MRSA was isolated commonly from lacrimal sac infection 89 (32%), lid infection 55 (20%), keratitis 45 (16%) and orbital infection 34 (12%). MRSA isolates showed 100% sensitivity to vancomycin, 91% to chloramphenicol and majority of MRSA isolates were resistant to all fluoroquinolones. MSSA strains showed very minimal resistance to chloramphenicol (5%) and also there was no resistance to vancomycin. In case of the MSSA isolates, resistance to fluroquinolones (ciprofloxacin, gatifloxacin, moxifloxacin, ofloxacin and levofloxacin) was found to increase during study period. Methicillin-resistance is conferred by the carriage of Staphylococcal Cassette Chromosome mec (SCCmec) and most of our isolates were belonged to SCCmec type V and IV which is known to be community acquired MRSA. MLST sequencing on seven housekeeping genes revealed, sequence type ST772 was predominant followed by ST22. Agr typing identified most of the isolates (69) were agr type II (77%). By spa typing, there are 16 spa types were identified, among which 60% of the isolates had t657 spa type.