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Updated: Nov 8, 2025
Biosensor for Detection of Antibiotic Resistant Staphylococcus Bacteria
Published on: May 8, 2013
Comparison of PCR and phenotypic methods for the detection of methicillin resistant Staphylococcus aureus
Anitha Madhavan1, Arun Sachu2, Anukumar Balakrishnan3
1Department of Microbiology, Government TD Medical College, Alappuzha, Kerala, India.
Background And Objectives:
Resistance to methicillin in methicillin resistant strains of Staphylococcus aureus (MRSA) is due to the presence of mec-A gene, which encodes a low affinity penicillin binding protein (PBP)-2a or PBP2. Accurate and rapid identification of MRSA in clinical specimens is essential for timely decision on effective treatment. The aim of the study was to compare three different methods for detection of MRSA namely cefoxitin disc diffusion, CHROM agar MRSA and VITEK-2 susceptibility with PCR which is the gold standard reference method and to find the antibiotic susceptibility pattern of these isolates by VITEK-2.
Materials And Methods:
A Total of 100 non-duplicate S. aureus isolates were collected from different clinical samples among both outpatient and inpatients. Detection of MRSA among these isolates was done by cefoxitin disc diffusion, VITEK-2, CHROM agar MRSA and PCR.
Results:
The sensitivity and specificity of cefoxitin disc diffusion and Vitek was found to be 97.2% and 100%, while that of CHROM agar was found to be 100% and 78.6%. The overall prevalence of MRSA in our study by PCR was 72%.
Conclusion:
Based on the findings in our study, isolates which show cefoxitin zone diameter < 22 mm can be reported as MRSA. However, those isolates which have a zone diameter between 22-24 mm, should ideally be confirmed by PCR.
Insights
Accurate identification of methicillin-resistant Staphylococcus aureus (MRSA) is crucial for effective treatment. Cefoxitin disc diffusion and VITEK-2 showed high accuracy, while CHROM agar MRSA requires confirmation for certain results.
Area of Science:
- Clinical microbiology
- Infectious diseases
- Antimicrobial resistance
Background:
- Methicillin-resistant Staphylococcus aureus (MRSA) poses a significant clinical challenge due to its resistance mechanisms, primarily the mecA gene encoding PBP2a.
- Rapid and accurate MRSA detection is vital for guiding appropriate patient treatment and infection control strategies.
Purpose of the Study:
- To evaluate and compare the diagnostic performance of cefoxitin disc diffusion, CHROM agar MRSA, and VITEK-2 susceptibility testing against PCR for MRSA detection.
- To determine the antibiotic susceptibility patterns of identified MRSA isolates using VITEK-2.
Main Methods:
- A total of 100 non-duplicate Staphylococcus aureus isolates from clinical samples were analyzed.
- MRSA detection was performed using cefoxitin disc diffusion, VITEK-2 automated system, CHROM agar MRSA, and PCR as the reference standard.
Main Results:
- Cefoxitin disc diffusion and VITEK-2 demonstrated high sensitivity (97.2%) and specificity (100%).
- CHROM agar MRSA exhibited 100% sensitivity but lower specificity (78.6%).
- The overall prevalence of MRSA in the study population, as determined by PCR, was 72%.
Conclusions:
- Cefoxitin disc diffusion with a zone diameter < 22 mm is a reliable indicator for MRSA identification.
- Isolates with cefoxitin zone diameters between 22-24 mm necessitate confirmation by PCR to ensure accurate diagnosis.
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