Detection of carbapenem-resistant Enterobacteriaceae amongst neonates in a regional hospital in KwaZulu-Natal : screening for carbapenemase production and MIC correlation.

Abstract

Carbapenemases are the primary cause for the increase in carbapenem resistance in Gram- negative Enterobacteriaceae. These enzymes are β-lactamases and have the ability to hydrolyse almost all β-lactam antibiotics thereby inactivating carbapenems that are used for the treatment of severe nosocomial infections. Multiple CPE outbreaks and epidemics have been reported in several hospitals in South Africa since the year 2011. This resulted in an increase in the morbidity and mortality rates and are slowly disseminating globally among more vulnerable individuals including neonates. Therefore, the aim of the study was to determine appropriate techniques for the rapid detection of carbapenem-resistant Enterobacteriaceae (CRE) (including CPE) isolated from neonates from King Edward VIII Hospital as well as to determine the molecular mechanisms conferring carbapenemase production in this subset of isolates. A total of 94 Klebsiella pneumoniae and 41 Enterobacter cloacae samples were isolated in this study. Among these species 10 % (9/ 94) and 39 % (16/ 41) of K. pneumoniae and E .cloacae respectively, were resistant to the carbapenems based on the Kirby-Bauer susceptibility tests, microbroth-dilution and E-tests. However, screening for carbapenemase production using chromogenic agar (Brilliance™ CRE agar and ChromID® CARBA agar), Modified Hodge test and amoxycillin-clavulanate double disc synergy test did not correlate with these resistance patterns and exhibited false positive results possibly due to the presence of extended spectrum beta-lactamase (ESBL) production by these organisms. Due to such discrepancies in the phenotypic results, further detection for the presence of carbapenemases was performed using multiplex real-time PCR assays. This revealed the presence of the blaOXA-48 gene in only 1 K. pneumoniae isolate. Further molecular characterisation will be required to determine if alternate mechanisms of resistance are present in the resistant isolates detected in this study.