Abstract
Introduction: Staphylococcus aureus infections in current times have become challenging to treat because of advent of Methicillin Resistant Staphylococcus aureus (MRSA) strains which are concurrently resistant to a wide panel of drugs and posing a threat to clinicians and microbiologists globally. The optimal drug for treatment of such MRSA infections is vancomycin but strains with augmented Minimum Inhibitory concentration (MIC) for this drug also have surfaced. Objectives: To know the frequency of MRSA isolates in various clinical samples with their antimicrobial sensitivity patterns and to equate agar dilution and E-test methods for MIC determination of vancomycin to MRSA strains. Materials and Methods: A total of 50 non repeat clinical isolates of staphylococcus aureus isolates were collected from various clinical specimens and were tested for methicillin resistance using the cefoxitin disc diffusion test (30mg). All MRSA isolates were tested for specific MIC by agar dilution and E-test methods. Results: 29 (58%) isolates were resistant to cefoxitin (MRSA). 13.8% isolates had MIC of 4mg/ml for vancomycin (VISA) by both agar dilution and E-test methods. However by agar dilution method 25 (86.2%) isolates exhibited vancomycin MIC of ? 2 mg/ml and by E-test 68.9% of the isolates showed MIC ? 2 mg/ml. Conclusion: Multidrug resistant MRSA strains are on the rise and alternate drug of choice for these infections; vancomycin also is showing increased MIC so prudent use of this drug is advocated. E-test can detect MRSA strains with intermediate MIC values useful for detection of MIC creep so that vancomycin can be used rationally.
Highlights
Staphylococcus aureus infections in current times have become challenging to treat because of advent of Methicillin Resistant Staphylococcus aureus (MRSA) strains which are concurrently resistant to a wide panel of drugs and posing a threat to clinicians and microbiologists globally
Isolates showing inhibition zone size ≥ 22 were considered as sensitive (MSSA) and ≤ 21 mm were considered as resistant (MRSA) as per CLSI criteria for zone diameter breakpoints of Staphylococcus aureus for cefoxitin.[6]
Over-all 50 Staphylococcus aureus strains were isolated from various clinical specimens of which pus specimens contributed for bulk of the isolates (78%). 29 (58%) isolates were resistant to cefoxitin while 21 (42%) were sensitive to cefoxitin
Summary
Staphylococcus aureus infections in current times have become challenging to treat because of advent of Methicillin Resistant Staphylococcus aureus (MRSA) strains which are concurrently resistant to a wide panel of drugs and posing a threat to clinicians and microbiologists globally. Conclusion: Multidrug resistant MRSA strains are on the rise and alternate drug of choice for these infections; vancomycin is showing increased MIC so prudent use of this drug is advocated.
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