Antibiotic Susceptibility Pattern of Nosocomial Isolates of Staphylococcus aureus in a Tertiary Care Hospital, Nepal

Introduction: Methicillin resistant Staphylococcus aureus (MRSA), the most common cause of nosocomial infection has been a major cause of morbidity and mortality around the world. They are normally resistant to most of the antibiotics used in clinical practice. This study has been carried out to find out the resistance pattern among S. aureus. Methods: During November 2007 to June 2008, clinical samples from patients with nosocomial infection were processed for culture and sensitivity following standard methodology in microbiology laboratory, Tribhuvan University teaching hospital, Kathmandu, Nepal. Results: Among 149 Staphylococcus aureus isolates, highest resistance was observed against Penicillin (91.94%) followed by Fluoroquinolone (61.74%), Erythromycin (52.94%), Gentamicin (46.98%), Cotrimoxazole (42.95%), Tetracycline (40.94%) and others, whereas susceptibility was observed maximum against Chloramphenicol (94.85%) followed by Rifampicin (92.61%), Tetracycline (59.06%), Cotrimoxazole (57.04%), and others. None of the isolates were resistant to Vancomycin and Teicoplanin. Of these isolates 44.96 % of the isolates were Methicillin resistant S. aureus (MRSA). Resistance to Penicillin, Fluoroquinolone, Erythromycin, Gentamicin, Co-trimoxazole and Tetracycline were associated significantly with MRSA isolates (X(2)=8.779, p<0.05, X(2)=74.233, p<0.05, X(2)=84.2842, p<0.05, X(2)=108.2032, p<0.05, X(2)=88.1512, p<0.05 and X(2)=79.1876, p<0.05 respectively). Although most of the Methicillin sensitive S. aureus (MSSA) isolates were susceptible to both Rifampicin and Chloramphenicol, only Rifampicin susceptibility was significantly associated with them (X(2)=10.1299, p<0.05). Among three Biochemical tests for the detection of beta lactamase detection namely chromogenic, iodometric and acidimetric test, chromogenic test method had highest sensitivity and specificity. Conclusions: Since MRSA comprised a greater part of S. aureus isolates and were multi-resistant, patients infected by such strains should be identified and kept in isolation for hospital infection control and treated with second line of drug like vancomycin.