Evaluation of colorimetric nitrate reductase assay for rapid detection of methicillin resistance in clinical isolates ofStaphylococcus aureus.
OBJECTIVE
Methicillin resistant Staphylococcus aureus (MRSA) remains a major cause of health care-associated infections. Rapid detection of MRSA facilitates the early initiation of appropriate treatment and infection control. Hence, the present study was undertaken to standardize and evaluate the performance of rapid colorimetric nitrate reductase assay (NRA) for determining methicillin resistance in S.aureus.


METHODS
A total of 160 clinical isolates of S. aureus, (80 each of methicillin susceptible and methicillin resistant) were included in the study. Minimum inhibitory concentration (MIC) was determined by NRA and reference broth micro dilution (BMD) methods. Results of NRA were compared with BMD and analyzed.


RESULTS
For MRSA, the MIC values ranged from 4 to ≥ 16 μg/ml and for MSSA, ≤ 0.5 to 2 μg/ml. Category and essential agreement for NRA as compared with BMD were found to be 99.4 and 89.7 per cent, respectively. No minor or major discrepancy was observed. A single resistant isolate showed very major discrepancy.


CONCLUSIONS
Colorimetric NRA being an inexpensive test requiring no special equipment can be employed as an alternative method for rapid detection of MRSA in resource limited settings.
Department of Microbiology, Jawaharlal Institute of Postgraduate Medical Education & Research, Puducherry, India.
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Niveditha
Department of Microbiology, Jawaharlal Institute of Postgraduate Medical Education & Research, Puducherry, India.
Sujatha
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Sistla
D003124:Colorimetry / Q000379:methods*; D006801:Humans; D008712:Methicillin / Q000627:therapeutic use; D055624:Methicillin-Resistant Staphylococcus aureus / Q000201:enzymology / Q000302:isolation & purification*; D050901:Nitrate Reductase / Q000235:genetics / Q000302:isolation & purification*; D013203:Staphylococcal Infections / Q000175:diagnosis* / Q000235:genetics / Q000382:microbiology
D050901:Nitrate Reductase; D008712:Methicillin