COMPARISON OF THE SUSCEPTIBILITY OF ESBL-POSITIVE AND ESBL-NEGATIVE ISOLATES OF E. COLI AND KLEBSIELLA PNEUMONIAE TO ANTIMICROBIAL AGENTS

Abstract

The aim of this investigation was to compare the susceptibility between ESBL-positive and ESBL-negative isolates to different antimicrobial agents. Material and methods: A total of 1207 consecutive non-repeat isolates of E. coli and K. pneumoniae-Kp (E. coli-804, Kp-403) were obtained from different clinical specimens from patients hospitalized at the University Clinics in Skopje over a one year period. Conventional microbiological procedures for the isolation and detection of the strains were used. Susceptibility to beta-lactams and non-beta-lactams was determined by standard disk diffusion method and by automated method using Vitek (for determination of the MIC-minimal inhibitory concentration). A total of 251 isolates were selected (E. coli-126 and K. pneumoniae-125) using tests for phenotypic detection of the ESBL-production. A total of 233 randomly selected strains which were ESBL-negative by phenotypic tests (E.coli-130 and K.pneumoniae103) were used as a control strains for susceptibility testing. Results: Difference of the susceptibility to imipenem between ESBL-positive and ESBL-negative strains of E. coli and K. pneumoniae was not detected. Both groups of strains were 100% susceptible to imipenem. Considering the rest of the tested beta-lactams, as well as non-beta lactams and uroantiseptics, there was a difference in the susceptibility comparing both groups of strains of E. coli and K. pneumoniae. This was due to the fact that ESBL-negative strains were highly susceptible to all tested antimicrobial agents, unlike the ESBL-positive ones (except in cases of cotrimoxazole and nitrofurantoin, where the difference in susceptibility between ESBL-positive and ESBL-negative strains of E. coli was not statistically significant, because both groups of strains were susceptible to those antimicrobial agents).These data are important for recommending adequate treatment of infections with ESBL-producing bacteria.