Abstract
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.
Highlights
Methicillin-resistant Staphylococcus aureus (MRSA) is aGram-positive bacterium that has developed antibiotic resistance to all penicillins and has become a major health problem since it was first identified (Barrett et al., 1968)
9 isolates were unable to grow on Oxacillin Resistance Screening Agar Base (ORSAB) suggesting that they were sensitive to oxacillin and presumed as methicillinsensitive S. aureus (MSSA)
We detected MRSA isolates by the ability to grow on ORSAB medium and by disc diffusion assay
Summary
Methicillin-resistant Staphylococcus aureus (MRSA) is aGram-positive bacterium that has developed antibiotic resistance to all penicillins and has become a major health problem since it was first identified (Barrett et al., 1968). Emergence of new MRSA strains as public health threat has recently been reported (Grundmann et al., 2006; Yamamoto et al, 2010). This bacterium can cause nosocomial and community-acquired infections ranging from minor skin infections to serious life-threatening diseases such as bacteraemia and invasive endocarditis (Chambers, 2001; Enright et al, 2002; Wisplinghoff et al., 2004). Methicillin was the first penicillinase-resistant penicillin to be used in the treatment of S. aureus infections. It was recognized as the most reliable agent for routine susceptibility testing and resistant strains were termed methicillin-resistant S. aureus (MRSA). Methicillin was replaced by oxacillin and the term oxacillin- resistant S
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