Investigation of the effectiveness of using combination disc tests based on the direct beta-lactam inactivation method for the rapid detection and characterization of carbapenemase producing Enterobacterales strains from positive blood culture bottles

Antimicrobial resistance is gradually increasing against carbapenems, which are the last choice in the treatment of infections caused by Enterobacterales, one of the main causes of community and hospital-acquired infections and carbapenem resistance is mainly caused by the production of carbapenemase enzymes. Early detection of carbapenemase enzymes is crucial for the appropriate management of treatment and infection control. In this study, the effectiveness of the direct beta-lactam inactivation method combined with combination disk test-based phenotypic methods (dBLIMplus) was evaluated in the rapid detection and carbapenemase characterization of carbapenemase-producing Enterobacterales strains from positive blood culture bottles. Sixty strains (15 each of class A, B, D carbapenemase positive and 15 carbapenemase negative by PCR), which were evaluated as the causative agent of hospital-acquired infection and identified as Escherichia coli or Klebsiella pneumoniae, were selected for dBLIMplus validation. dBLIMplus evaluation zone diameter criteria were determined by applying dBLIMplus to the validation strains. To evaluate the utility of dBLIMplus in the routine laboratory, dBLIMplus was applied to a total of 100 clinical strains identified as E. coli or K. pneumoniae. It was determined that it was more appropriate to evaluate dBLIMplus at the 6th hour and that dBLIMplus detected carbapenemase activity with 100% sensitivity and specificity, while carbapenemase characterization could be performed with 92.8% sensitivity and 100% specificity (Mc Nemar, p=0,125; Cohen Kappa ĸ=0,920). The correct Ambler class could be determined with dBLIMplus in 22/24 clinical strains (91.6%) in which a resistance gene belonging to a single carbapenemase class was detected. While the sensitivity of dBLIMplus in detecting class A carbapenemases was 87.5% and its specificity was 100%, its sensitivity in detecting class D carbapenemases was found to be 93.7% and its specificity was 98.8%. In conclusion, dBLIMplus can be suggested as a highly appropriate phenotypic method that can be used in routine laboratory applications, with over 90% compatibility with the reference method in the detection and characterization of carbapenemase activity directly from positive blood culture bottles. Rapid carbapenemase detection will accelerate antimicrobial management and infection control practices, as well as contribute to the reduction of antimicrobial resistance by limiting inappropriate antimicrobial use. Keywords: antimicrobial management, dBLIMplus, Enterobacterales, rapid detection, carbapenemase