Predicament in detection and reporting of extended spectrum beta lactamase production in routine antibiotic susceptibility testing

ABSTRACT

This descriptive and cross-sectional study was planned to determine the dilemma of inadvertent detection of extended spectrum beta lactamase [ESBL] production in Enterobacteriaceae when using inhibition zone size of antibiotic disks of Cefotaxime or Aztreonam in routine antibiotic susceptibility testing as recommended by Clinical Laboratory Standards Institute [CLSI]. Screening and double disk tests were adopted as per CLSI. Escherichia coli ATCC 25922 was used as control strain. Among total specimens of 5346, there were 348 isolates of Escherichia coli [n=235], Klebsiella pneumonia [n=92], Klebsiella oxytoca [n=3] or Proteus mirabilus [n=18]. The screening method recommended by CLSI significantly falsely detected ESBL production in 79 [32.3%] isolates [p<0.0001]. ESBL detection is important as its frequency is high and treatment of the infection varies with the presence and absence of ESBL. To avoid false reporting, proper phenotypic detection of ESBL confirmatory method-like double-disk synergy test, should be used routinely