Comparison of Four Phenotypic Assays and Check-Direct CPE for Detection of Carbapenemases-Producing Enterobacterales

Early and accurate detection of carbapenemase-producing Enterobacterales (CPE) is fundamental to prevent their spread in hospital environment. Our objective was to compare between four commonly used phenotypic assays and Check-Direct CPE (CDCPE) multiplex PCR in CPE detection. We examined stool samples or rectal swabs for CPE, samples collected from 23 Jan 2017 to 23 Jul 2017 from patients in intensive-care units (ICUs) of our hospital.

A panel of 98 non-repetitive Enterobacterales isolates with reduced susceptibility to carbapenems were analyzed by means of (i) Modified Hodge Test (MHT), (ii) Blue Carba test (BCT), (iii) Combined Disc Test (CDT), and (iv) The Carbapenem Inactivation Method (CIM). All these phenotypic tests compared with CDCPE. Confirmation and validation of results was achieved by classical PCR and sequencing.

Of the 98 non-repetitive Enterobacterales isolates, ninety-one were K. pneumoniae (93%), three K. oxytoca (3%), three E. cloacae (3%) and one E. coli (1%). By classic PCR the carbapenem resistance genes in K. pneumoniae isolates distributed as the followings; 49 blaOXA-48, 34 both blaOXA-48 and blaNDM-1, seven blaNDM-1 and one blaKPC. K. oxytoca; two blaOXA-48, one blaNDM-1. E. cloacae; two blaOXA-48, one blaNDM-1. E. coli; one isolate with both blaOXA-48 and blaNDM-1. The most common carbapenemase gene detected was blaOXA-48 rate of 54% (n = 53) followed by a combination of both blaOXA-48 and blaNDM-1 with rate of 36% (n = 35), only blaNDM-1 9% (n = 9) and blaKPC 1% (n = 1). Among phenotypic tests, we found CIM, MHT, and BCT correctly identified carbapenemase producers with sensitivity of 100%, 98%, and 90.8%, respectively.

Rapid and accurate detection of CRE can be achieved by combination of both phenotypic and molecular tests. Surveillance studies are important both in terms of epidemiology and regulation of the treatment of patients.