Evaluation of different methods of identification of methicillin-resistant Staphylococcus aureus (MRSA); antibiogram and plasmid profile of hospital and community-acquired strains

Nosocomial infections by methicillinresistant Staphylococcus aureus (MRSA) represent an increasing problem in hospitals. The aims of this study were to assess the prevalence of MRSA in Shebin El-Kom Teaching Hospital, to evaluate oxacillin screen agar, oxacillin disc diffusion and E-test in the identification of MRSA, to analyze the plasmid profile and know the role of hospital staff in transmition of infection within the hospital. The results of the present study showed that Staph. aureus constituted 40.2% of all nosocomial infections and that 76 out of the isolated 177 Staph. aureus strains were resistant to oxacillin (66 MRSA strains were isolated from 132 inpatients, 7 from 25 outpatients, and 3 from 38 medical staff). All isolated MRSA strains were multi-drug resistant with a high rate of resistance to penicillin, ampicillin, oxacillin, amoxicillin-clavulanate, cephalexin, ceftriaxone, erythromycin, tetracycline and gentamycin. On the other hand, they were mostly sensitive to rifampicin, clindamycin, vancomycin and teicoplanin. Oxacillin screen agar base (ORSAB) was more sensitive as compared to both E- test and oxacillin disk diffusion in detecting MRSA (76 MRSA isolates were identified by ORSAB while 73 and 72 MRSA strains were detected by the Etest and disc diffusion respectively). Plasmid profile analysis showed that 55 (72.4%) MRSA strains harboured plasmids, while 21(27.6%) were plasmidless. The molecular weight of plasmids ranged from 1.2 to 23 MDa and the number of plasmids per isolate ranged from 1 to 5. Nine out of 27 MRSA strains isolated from clinical sites contained a 1.4 MDa plasmid which was occasionally present in strains isolated from medical staff who had an antibiotic resistance pattern which was similar to patients strains. In conclusion, multi-drug resistant MRSA strains are important cause of nosocomial infection. Most of them contained plasmids which may be responsible for antibiotic resistance. Oxacillin screen agar may be a reliable and rapid method for identification of MRSA. Surveillance of medical staff for MRSA carriage may be helpful in detecting carriers and subsequent better control of MRSA spread.