Prevalence of methicillin resistant Staphylococcus aureus and resistance pattern of its clinical strains to beta-lactam antibiotics

Staphylococcus aureus is the leading overall cause otf nosocomial infections with increasing resistance to β lactam antibiotics. This study was carried out to study the current resistant/susceptibility pattern of S. aureus to β lactam antibiotics and prevalence of Methicillin Resistant S. aureus (MRSA) in the studied population. Clinical isolates of S. aureus strains were collected from Medical Microbiology Unit of University College Hospital, Ibadan between May and October, 2012. The isolates were confirmed through growth on Mannitol Salt Agar (MSA) and tube coagulase test. The susceptibility / resistance pattern of the S. aureus strains to antibiotics were tested by disc diffusion method. Fifty studied S. aureus strains were highly resistant to Amoxycillin (92%), Aztreonam (70%), but high susceptibility was observed to Imipenem (90%), Cefotaxime (62%), Ceftazidine (50%), Cefoxitin (66%), Ceftriazone (52%), Amoxycillin/Clavulanic acid (50%), S. aureus strains (42%) that were resistant to amoxicillin were susceptible to amoxicillin/clavulanic acid while 34% of the studied S. aureus strains were MRSA. The relatively high prevalence of MRSA in the studied S. aureus strains call for surveillance studies and implementation policies in control of MRSA. Cephalosporins are still relatively effective for treatment of S. aureus infections. The observed synergy in this study between imipenem and aztreonam is an indication that combine therapy of imipenem and aztreonam will lead to enhanced antimicrobial activity of aztreonam.