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Updated: Aug 14, 2026

Biosensor for Detection of Antibiotic Resistant Staphylococcus Bacteria
Published on: May 8, 2013
Effect of source of Mueller-Hinton agar on detection of oxacillin resistance in Staphylococcus aureus using a
Abstract:
Dehydrated Mueller-Hinton agar from five different manufacturers was used to prepare plates containing 4% NaCl and 6 micrograms of oxacillin per ml to screen for oxacillin resistance in Staphylococcus aureus. A total of 137 isolates which included 109 oxacillin-resistant isolates obtained from at least eight geographic areas were examined. Results were compared to MICs obtained by using a standard broth microdilution method. Results obtained with screening plates prepared with dehydrated media from three of the manufacturers showed 100% correlation with MICs in detecting oxacillin-resistant S. aureus, and plates prepared with the remaining two media identified oxacillin resistance in 90 and 99% of the resistant isolates, respectively. None of the oxacillin-susceptible isolates grew on any of the screening plates. This study demonstrated that oxacillin screening plates are reliable for detecting oxacillin-resistant S. aureus; however, the source of Mueller-Hinton agar can influence the results.
Insights
Oxacillin screening plates reliably detect oxacillin-resistant Staphylococcus aureus. However, the specific Mueller-Hinton agar manufacturer can impact the accuracy of these crucial diagnostic tests.
Area of Science:
- Microbiology
- Clinical Diagnostics
- Antimicrobial Resistance
Background:
- Staphylococcus aureus is a significant pathogen, and oxacillin resistance is a growing concern.
- Accurate and rapid detection of oxacillin resistance is crucial for effective treatment strategies.
Purpose of the Study:
- To evaluate the reliability of oxacillin screening agar plates for detecting oxacillin-resistant Staphylococcus aureus (ORSA).
- To assess the influence of different Mueller-Hinton agar manufacturers on screening plate performance.
Main Methods:
- Dehydrated Mueller-Hinton agar from five manufacturers was used to prepare screening plates with 4% NaCl and 6 µg/mL oxacillin.
- 137 Staphylococcus aureus isolates (109 resistant, 28 susceptible) from diverse geographic areas were tested.
- Results were compared against minimum inhibitory concentrations (MICs) determined by broth microdilution.
Main Results:
- Screening plates from three manufacturers showed 100% correlation with MICs for detecting ORSA.
- Plates from the remaining two manufacturers demonstrated 90% and 99% correlation, respectively.
- No oxacillin-susceptible isolates grew on any screening plates, indicating high specificity.
Conclusions:
- Oxacillin screening agar plates are a reliable method for detecting oxacillin-resistant Staphylococcus aureus.
- The performance of these screening plates can be influenced by the brand of dehydrated Mueller-Hinton agar used.
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