Comparison of Disc Diffusion and E test methods for Antimicrobial Susceptibility Testing Of Vancomycin in Coagulase Negative Staphylococcus Isolated from Blood Culture

  Background and Objective: Reliable methods of detection of antimicrobial resistance are of paramount importance in the treatment and management of infections caused by coagulase negative staphylococci (CoNS). The objective of the present study was to compare and evaluate the performance of disc diffusion and E test (Epsilometer test) methods for antimicrobial testing of coagulase negative staphylococci in blood cultures. Materials and Methods: A total of 77 isolates of coagulase negative staphylococci from blood cultures were included as test strains. Antimicrobial susceptibility testing was performed by disc diffusion method for vancomycin. Minimum inhibitory concentration (MIC) determination was performed by E test for the same antimicrobial agent. All tests were performed on Mueller Hinton media. Results: Disc diffusion showed four resistant and 73 susceptible cases in examined strains with vancomycin. E test showed susceptibility of all strains to vancomycin. Decreased susceptibility to vancomycin were detected in 20 isolates in disc diffusion method but in 18 isolates by E test method Conclusion: Disc diffusion test may be used as a preliminary screening method for susceptibility testing of coagulase negative staphylococci. E test is a simple, easy and reliable method for determination of resistance in coagulase negative staphylococci, however, cost and limited availability in Iran limits its use.