Sensitive and specific detection of carbapenemase-producing carbapenem resistant Enterobacteriaceae in the routine microbiology laboratory with modified Hodge test and CarbaNP test

Abstract

Carbapenemase-producing carbapenem resistant Enterobacteriaceae (CP-CRE) are of major clinical and public health concerns due to the highly transmissible nature and the lack of therapeutic options. Rapid and reliable detection of CP-CRE in the routine clinical microbiology laboratory is critical for the timely optimisation of therapy and implementation of infection control measures. This study aims to evaluate the performance of the various phenotypic methods that are available in our laboratory. 312 carbapenem intermediate or resistant Enterobacteriaceae isolates were tested for carbapenemase production using the modified Hodge test (MHT), the CarbaNP test, the MAST Carbapenemase Detection Test (MASTDISCS D70C) and the KPC/MBL and OXA-48 Kit (ROSCO Diagnostica). The phenotypic test results were compared against molecular detection of the carbapenemase genes via polymerase chain reaction (PCR). In our laboratory, the MHT had a sensitivity of 95.8% and a specificity of 87.7%. The CarbaNP test had a sensitivity of 96.6% and a specificity of 93.7%. Combining the MHT and CarbaNP test improved the sensitivity to 100%, with a positive predictive value of 97% and a negative predictive value of 100%. In conclusion, the combination of MHT and CarbaNP test represents the most sensitive and cost effective methods of CP-CRE phenotypic detection in our laboratory.