In vitro susceptibility of chloramphenicol against methicillin-resistant Staphylococcus aureus

To determine the in vitro susceptibility of chloramphenicol against methicillin-resistant Staphylococcus aureus.

Cross-sectional study.

Department of Microbiology, Armed Forces Institute of Pathology, Rawalpindi, from January to June 2012.

One hundred and seventy four isolates of methicillin-resistant Staphylococcus aureus were included in this study using cefoxitin (30 μg) disc for detection. Minimum inhibitory concentration (MIC) of chloramphenicol against MRSA was determined by using E-strip (AB BIO DISK). The susceptibility was determined by swabbing the Mueller-Hinton agar (MHA) plates with the resultant saline suspension of MRSA and applying E-strip of chloramphenicol from AB Biodisk Sweden and determining the MIC of chloramphenicol (in μg/ml). Clinical and Laboratory Standards Institute (CLSI) recommendations of ≤ 8 μg/ml being sensitive, 16 μg/ml as intermediate and ≥32 μg/ml as resistant were followed in interpreting the results.

Out of the 174 MRSA isolates, 132 (75.86%) isolates were susceptible to chloramphenicol with MICs of ≤ 8 μg/ml, 38 (21.84%) were resistant ≥32 μg/ml while 4 (2.30%) were in intermediate range with MIC of 16μg/ml.

Chloramphenicol has shown good in vitro activity against MRSA and is likely to have a key role in the treatment of MRSA infections providing us a good alternative to newer expensive antimicrobials in resource limited countries.