β-lactamase enzymes inactivate β-lactam antibiotics and render them ineffective for the treatment of clinically important Gram-negative bacterial infections. Now, two new kits from Streck, available in the UK from Alpha Laboratories, provide a comprehensive, cost-effective molecular method to detect the most clinically important β-lactamases that confer resistance to penicillins, cephamycins and, in some cases, carbapenems.
The antibiotic resistance monitoring and detection (ARMD) kits are multiplex real-time polymerase chain reaction (PCR) kits that can detect more than 450 β-lactamase gene variants quickly. The ARMD kit, β-Lactamase, detects nine different carbapenemases, extended-spectrum b-lactamases (ESBLs) and plasmid-mediated ampC gene families. The ARMD Kit, ampC, targets six plasmid-mediated ampC resistance gene families and can differentiate plasmid-mediated AmpC β-lactamase resistance from chromosomal resistance.
These genotypic detection methods identify the most prevalent types of β-lactamase-based antibiotic resistance and complement phenotypic methods for the detection of multidrug-resistant organisms. They can be used with standard susceptibility tests to improve surveillance and epidemiological tracking, for improved infection control and increased effectiveness of antibiotic stewardship programmes.
AmpC β-lactamases are chromosomally encoded in many bacterial species. Their over-expression can lead to resistance to most β-lactam antibiotics, causing therapeutic failure. Transmissible plasmids with acquired genes for AmpC β-lactamases
often cause increased β-lactamase production and can appear in organisms lacking or having low-level expression of a chromosomal ampC gene. Resistance due to plasmid-mediated AmpC enzymes can be broad in spectrum and often hard to detect. As Gram-negative organisms producing multiple or plasmid-mediated β-lactamases are difficult to identify phenotypically, more specific detection methods are essential for the identification of clinically important β-lactamases, and selection of the appropriate antibiotic therapy.
Detection and genetic identification of both plasmid-mediated and chromosomally expressed AmpC β-lactamases are crucial for better understanding of these resistance mechanisms and, consequently, for active surveillance and infection control.