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

Abstract

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 fi nd 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 signifi cantly with MRSA isolates (X2= 8.779, p<0.05, X2= 74.233, p<0.05, X2= 84.2842,
p<0.05, X2= 108.2032, p<0.05, X2= 88.1512, p<0.05 and X2= 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 signifi cantly associated with them (X2=
10.1299, p<0.05). Among three Biochemical tests for the detection of β lactamase detection namely
chromogenic, iodometric and acidimetric test, chromogenic test method had highest sensitivity and
specifi city.
Conclusions: Since MRSA comprised a greater part of S. aureus isolates and were multi-resistant,
patients infected by such strains should be identifi ed and kept in isolation for hospital infection
control and treated with second line of drug like vancomycin.
Key Words: β lactamase, methicillin resistant Staphylococcus aureus,
methicillin sensitive Staphylococcus aureus, resistance pattern