Detection of Carbapenemase Production in Gram-negative Bacteria

Abstract

The greatest threat to antimicrobial treatment of infections caused by Gram-negative bacteria is the production of carbapenemases. Metallo-beta-lactamases and plasmid-mediated serine carbepenemases like Klebsiella pneumonia carbapenemase are threatening the utility of almost all currently available beta-lactams including carbapenems. Detection of organisms producing carbapenemases can be difficult, because their presence does not always produce a resistant phenotype on conventional disc diffusion or automated susceptibility testing methods. These enzymes are often associated with laboratory reports of false susceptibility to carbapenems which can be potentially fatal. Moreover, most laboratories do not attempt to detect carbapenemases. This may be due to the lack of availability of guidelines and procedures or lack of knowledge and expertise. Because routine susceptibility tests may be unreliable, special tests are required to detect the resistance mechanisms involved. This document describes the standard methodology for detection of various types of carbapenemases, which can be put to use by laboratories working on antimicrobial resistance in Gram-negative bacteria.

Keywords: Carbapenemases; Gram-negative bacteria; Klebsiella pneumoniae carbapenemase; New Delhi metallo-beta-lactamase; metallo-beta-lactamases.

Figure 1

E-test showing carbapenemase production

Figure 2

Modified Hodge test

Figure 3

Phantom zone in E-test indicating carbapenemase production

Figure 4

Different methods of detection of metallo-beta-lactamase and Klebsiella pneumoniae carbapenemases