Prospective evaluation of the efficiency of phenotypic tests used in detection of carbapenemase-producing enterobacteriaceae

The Enterobacteriaceae family is the causative agent of both simple community-acquired infections and complex hospital-associated infections. Today, resistance to carbepenems, which is one of the last-choice treatments for Enterobacteriaceae, is becoming widespread due to increasing antimicrobial drug resistance. Surveillance networks have been established around the world due to the rapid spread of CRE isolates and the increase in morbidity and mortality due to infections. The data obtained here warns that BDE isolates spread horizontally between patients in health care institutions and now spreads in the society and threatens public health. For this reason, rapid and accurate detection of these isolates is important in preventing their spread by taking infection control measures. The most common cause of CRE's is the production of carbapenemases. The gold standard for the diagnosis of carbapenemases is molecular methods. However, it cannot be used widely due to experienced personnel, cost and well-equipped laboratory requirements. In our study, we aimed to evaluate the performance of phenotypic tests used in diagnosis. 100 K.pneumoniae isolate included to study that has been isolated from samples sent to our laboratory from various clinics of our hospital between 2018 and 2021. EUCAST 2021 criteria were used as carbapenemase screening criteria. Combined disk method, mCIM and aCIM tests were performed to detect the presence of carbapenemase on the isolates. The mCIM and aCIM tests were evaluated separately according to the 19 and 22 mm inhibition zone diameter cutoff threshold values. Combined disk method, eCIM and CIMplus methods were studied to detect the carbapenemase species and the results were compared. Resistance gene detection was performed on each of the isolates by real-time PCR. The sensitivities of combined disc method, mCIM-19 mm, mCIM 22 mm, aCIM-19 mm, aCIM-22 mm tests as 100%, 83.8%, 94.8%, 82.7%, 94.6%, and the specificities as 83.3%, 100%, 34%, 100%, 57% respectively, for detection of carbapenemases. The sensitivites of combined disc method, eCIM-19 mm, eCIM-22 mm, CIMplus tests as 100%, 75,4%, 84%, 23%, and the specificites as 62,5%, 48,8%, 44%, 100% respectively, for detection of carbapenemase species. We could not detect a significant difference between the results of the mCIM and aCIM tests. We observed that when we increased the inhibition zone diameter threshold value of the mCIM, aCIM and eCIM tests from 19 mm to 22 mm, the sensitivity increased and the specificity decreased. We believe that the most effective results in terms of both performance and functionality will be achieved with the combined disk method. We think that phenotypic tests will be insufficient for isolates containing double resistance genes. Key words: Carbapenem resistant Enterobacteriaceae, carbapenemase, combined disc method, carbapenem, inactivation method