Detection of high levels of methicillin and multi-drug resistance among clinical isolates of Staphylococcus aureus

Methicillin-resistant Staphylococcus aureus (MRSA) has become a frequent cause of serious infections worldwide. We identified clinical isolates of S. aureus using conventional methods based on morphological and biochemical characteristics. Resistance of isolates to oxacillin was tested by growth on Oxacillin Resistance Screening Agar Base (ORSAB) and disc diffusion method. Oxacillin MICs were determined by agar dilution method. Sensitivity of isolates to a range of antibiotics was also tested by disc diffusion method. We further confirmed methicillin resistance using a PCR-based molecular approach. Data revealed that among 120 clinical bacterial samples tested 81 were confirmed as S. aureus. Out of these 81 isolates, 72 were MRSA (88.9%). The distribution of resistance among MRSA isolates was alarming. Twenty (20) MRSA isolates (27.8%) showed the highest level of resistance detected in this study with oxacillin MIC >6400 μg/ml. Most isolates were also resistant to multiple antibiotics. PCR results revealed the detection of mecA gene responsible for resistance in all tested isolates and therefore confirmed the conventional identification of MRSA isolates. The present study provides additional evidence that the rate of emergence of MRSA is in a continuous increase. Key words: Staphylococcus aureus, MRSA, mecA gene, methicillin resistance, multi-drug resistance.