Erroneous reporting of vancomycin susceptibility for Staphylococcus spp. by Vitek software version 2.01.

Area of Science:

• Clinical microbiology
• Antimicrobial resistance
• Medical diagnostics

Background:

• Vancomycin resistance in Staphylococcus species presents significant therapeutic and epidemiological challenges.
• Accurate susceptibility testing is vital for guiding patient treatment and monitoring resistance trends.

Purpose of the Study:

• To evaluate the performance of Vitek software version 2.01 for vancomycin susceptibility testing in Staphylococcus species.
• To compare Vitek 2.01 results against reference methods like broth dilution, vancomycin screen agar, and Etest.

Main Methods:

• Testing of 105 Staphylococcus isolates.
• Utilized CLSI-recommended broth dilution, CDC-recommended vancomycin screen agar, and Etest as reference methods.
• Compared results obtained from Vitek 2.01 automated system with reference methods.

Main Results:

• Vitek 2.01 incorrectly identified 16 out of 105 isolates (15%) as having intermediate or resistant vancomycin phenotypes.
• Discrepancies highlight potential inaccuracies in automated susceptibility testing for vancomycin resistance.

Conclusions:

• Automated systems like Vitek 2.01 may produce false vancomycin resistance reports in Staphylococcus species.
• Laboratories must implement validated confirmatory methods to verify vancomycin resistance detected by automated systems.