Application of PCR based - RFLP for species identification of ocular isolates of methicillin resistant staphylococci (MRS).

ABSTRACT

Background & objectives: Early detection of methicillin resistant staphylococci (MRS) from clinical specimens enables institution of appropriate antimicrobial therapy. Limited information is available on speciation of MRS. This study was undertaken to compare results of conventional and molecular methods in detection of methicillin resistance (MR) and application of PCR-restriction fragment length polymorphism (RFLP) and DNA sequencing for speciation of ocular isolates of MRS. Methods: A total of 110 consecutive ocular staphylococcal isolates were screened for MR. MRS was speciated by PCR-RFLP of gap gene and results were confirmed by DNA sequencing. All isolates were processed within 48 h of isolation. A single colony of bacterium, stocked as stab cultures in Hyer’s and Johnson agar, was stored at 40C and sub-cultured at every 15 days interval. Results: Seventy (63.6%) of 110 isolates were identified as MRS and 40 (36.4%) were MSS by conventional and molecular method (100% correlation). Of the 70 MRS, 18 (25.7%) were Staphylococcus aureus, remaining 52 (74.3%) were CNS by conventional and molecular method (100% correlation). PCR-RFLP of gap gene identified 18 (25.71%) MRS as S. aureus, 11 (15.71%) S. epidermidis, 27 (38.57%) S. haemolyticus, 6 (8.57%) S. cohnii subsp. urealyticum, 6 (8.57%) S. equorum, 1 (1.42%) S. xylosus and 1 (1.42%) S. hominis. Interpretation & conclusions: Overall rate of isolation MRS was 63.6 per cent and were predominantly isolated from conjunctival swab (23.6%) and donor corneal scleral rim (23.6%) of non hospitalized patients indicating their community origin. Detection of MR by mecA gene was easier and less time consuming compared to conventional methods. Speciation of MRS was possible by gap gene PCR - RFLP and the predominant MRS in our study was S. haemolyticus.