Occurrence of vancomycin MIC creep in methicillin resistant isolates in Saudi Arabia

Abstract

Background: "MIC creep" is a phenomenon that describes an increase of an organism MICs over time and have been reported from different parts of the world. High MIC in MRSA has been theoretically liked to treatment failure and may be a precursor to hVISA and VISA. This study was conducted to assess presence of vancomycin minimum inhibitory concentration (MIC) creeps among clinical isolates of methicillin-resistant Staphylococcus aureus (MRSA) in Saudi Arabia.

Methods: Minimum inhibitory concentration (MIC) of vancomycin by E test of all MRSA isolates of from 2013 to 2018 were reviewed.

Results: Of the 736 isolates evaluated, no isolates with MIC above 2 were found. Majority of MRSA isolates were susceptible to vancomycin with MIC less than 1. There was a significant increase in both Arithmetic and geometric mean MIC for vancomycin during the first three years which progressively declined in the next three years.

Conclusions: Although most of MRSA isolated remained very susceptible to vancomycin there was evidence of dynamic vancomycin MIC creep over time.

Keywords: MIC creep; MRSA; VANCOMYCIN.