Detection of methicillin-resistant Staphylococcus epidermidis.

Area of Science:

• Microbiology
• Clinical Diagnostics
• Antimicrobial Resistance

Background:

• Methicillin-resistant Staphylococcus aureus (MRSA) detection methods are widely used.
• The effectiveness of these methods for identifying methicillin-resistant Staphylococcus epidermidis (MRSE) is less understood.
• Accurate MRSE detection is crucial for patient care and infection control.

Purpose of the Study:

• To evaluate the performance of various susceptibility testing methods for detecting MRSE.
• To compare MRSE detection rates using different incubation times, media supplements, and inoculum preparations.
• To determine the optimal method for reliable MRSE identification.

Main Methods:

• Tested 135 S. epidermidis isolates using Vitek AMS, agar screen, disk diffusion, and microdilution methods.
• Modified methods included 24- vs. 48-h incubation, NaCl-supplemented vs. unsupplemented broth, and standard vs. direct inoculum.
• Evaluated oxacillin and methicillin resistance using different concentrations and testing formats.

Main Results:

• Oxacillin disk diffusion at 24 hours detected the most resistant strains (59), with 3 additional strains identified at 48 hours.
• Oxacillin disk diffusion and agar screen showed comparable results at 24 and 48 hours.
• Vitek AMS identified 50 resistant strains; methicillin-based methods with NaCl supplementation detected fewer resistant strains at 24 hours.

Conclusions:

• Direct inoculum with 24-hour oxacillin disk diffusion and reincubation is recommended for MRSE detection.
• Alternatively, 24-hour oxacillin agar screen with 48-hour incubation for non-growing strains is a viable option.
• These methods ensure more accurate identification of methicillin-resistant Staphylococcus epidermidis.