Detection of carbapenemase producing Enterobacterales by MALDI-TOF mass spectrometry in Samutprakan Hospital, Thailand

Abstract

A rapid phenotypic carbapenemase-producing Enterobacterales (CPE) detection method was established using Matrix Assisted Laser Desorption Ionization-Time of Flight Mass Spectrometry (MALDI-TOF MS). Sixtyfour carbapenem-resistant Enterobacterales (CRE) strains from Samutprakan Hospital were examined using MALDI-TOF MS by the ertapenem hydrolysis method and the susceptibility was compared with a modified carbapenem inactivation method (mCIM). Drug resistance genes were detected by polymerase chain reaction (PCR). The ertapenem drug and bacterial strains were mixed and drug hydrolysis owing to CPE activity was confirmed by specific molecular masses of ertapenem [M+H]+ at 476.5 m/z (±500 ppm), with peak disappearance judged as carbapenemase-positive. The most common CRE species were Klebsiella pneumoniae, Escherichia coli, and Enterobacter cloacae. From 58 CPE strains, 17 strains of K. pneumoniae (29.3%) harbored blaNDM and blaOXA48- like genes together, while 33 strains of K. pneumoniae (56.9%), 6 strains of E. coli (10.3%) and 1 strain of Ent. cloacae (1.75%) carried blaNDM or blaOXA-48- like genes alone and 1 strain of K. pneumoniae (1.75%) contained blaKPC. After 3 h of incubation with ertapenem, all 58 drug-resistant strains revealed disappearance of the ertapenem-specific waveform peak at 476.5 m/z, whereas 6 strains of CRE (non-CPE) revealed the ertapenemspecific waveform peak. The MALDI-TOF MS and mCIM data were 100% consistent. The MALDI-TOF MS based ertapenem hydrolysis assay was demonstrated as a rapid and accurate method to detect carbapenemase activity of Enterobacterales strains that can be routinely performed in clinical microbiology laboratories.