Performance evaluation of cefoxitin screen test on two different automated antimicrobial susceptibility test systems:...

Area of Science:

• Clinical Microbiology
• Antimicrobial Resistance
• Diagnostic Technology

Background:

• Accurate detection of beta-lactam resistance mediated by mecA and mecC genes is crucial for effective patient management.
• Automated antimicrobial susceptibility testing (AST) systems are widely used for rapid susceptibility results.

Purpose of the Study:

• To compare the performance of the Vitek 2 and BD Phoenix automated systems in detecting mecA/mecC-mediated beta-lactam resistance.
• To evaluate the new cefoxitin screen test on Vitek 2 against reference methods and the BD Phoenix system.

Main Methods:

• Evaluated 250 Staphylococcus isolates (120 mecA-positive, 10 mecC-positive, 120 negative).
• Performed cefoxitin screen and oxacillin tests on Vitek 2 and BD Phoenix, comparing with disk diffusion and broth microdilution reference methods.
• Utilized PCR for confirmation of mecA and mecC genes.

Main Results:

• Vitek 2 cefoxitin screen: 100% sensitivity, 98% specificity vs. reference.
• BD Phoenix cefoxitin screen: 84% sensitivity, 100% specificity vs. reference.
• Combined cefoxitin and oxacillin tests improved Phoenix sensitivity to 100% with unchanged specificity.

Conclusions:

• The Vitek 2 cefoxitin screen demonstrates high sensitivity for detecting mecA/mecC-mediated resistance.
• Both Vitek 2 and BD Phoenix achieve high performance when using a combination of cefoxitin and oxacillin tests.
• These findings support the reliable use of these automated systems in clinical settings.