Molecular Detection of Bacteria Producing Newer Types of β-Lactamases

In Gram-negative pathogens, β-lactamase production remains the most important contributing factor to β- lactam resistance. β-lactamases are bacterial enzymes that inactivate β-lactam antibiotics by hydrolysis, which results in ineffective compounds. The three major groups usually referred to as the "newer β-lactamases" are plasmid-mediated AmpC enzymes, extended-spectrum β-lactamases (ESBLs) and carbapenem-hydrolyzing enzymes (including metallo-β- lactamases [MBLs]). Molecular methods that include simple and multiplex PCR, real-time PCR, DNA sequencing and various hybridization-based techniques are used widely in research and reference laboratories for the detection of organisms producing newer β-lactamases. The routine screening in clinical diagnostic laboratories of organisms producing TEM, SHV and OXA types of ESBLs using genotypic methods remains problematic, while the detection of CTX-Ms, plasmid-mediated AmpCs and MBLs shows clinical usefulness. Molecular methods have advantages over phenotypic tests by accurately detecting resistant genes in a rapid fashion and by defining the precise genetic basis of the resistance mechanism providing important information valuable to the early introduction of infection control practices. Molecular assays have the potential to complement conventional phenotypic susceptibility techniques and impact directly on patient care.