Table 3 Overview of AmpC detection methods
From: Innovative approaches in phenotypic beta-lactamase detection for personalised infection management
Method | Overview | Quantitative (✓ / X) | |
|---|---|---|---|
Phenotypic | AmpC Disc Diffusion Test | Involves using antibiotic discs alone and in combination with beta-lactamase inhibitors. Resistance to cefoxitin and enhancement of the inhibition zone with inhibitors like boronic acid or cloxacillin suggest AmpC production | X |
Disc Potentiation Test (DPT) | Similar to DDST, involves testing with three different enzyme inhibitors. Discs of cephalosporin and cephalosporin plus inhibitor are added to a lawn culture and zone size is measured after incubation | X | |
Double Disc Synergy Test (DDST) | Involves testing with three different enzyme inhibitors (boronic acid, cloxacillin at two concentrations). The test aims to assess AmpC enzyme activity in the organisms by evaluating the inhibitory effect of cephalosporin antibiotics in the presence of these inhibitors. The principle is based on the inactivation of AmpC enzyme by the inhibitors, leading to an increased zone of inhibition around the cephalosporin | ||
Gradient test | Gradient of cephamycin and cephamycin combined with a gradient of cloxacillin on respective half of the E-strips are used for the detection of AmpC producers A reduction in the MIC of cephamycin for at least three dilutions or deformation of its zone of inhibition or a “Phantom zone” suggests the presence of AmpC enzyme producers | X | |
Genotypic | Polymerase Chain Reaction (PCR) | Utilizes polymerase chain reaction to target genes associated with AmpC production, such as blaCMY, blaDHA, and blaACT e.g. Check-MDR CT103XL, Check Points Health | X |
DNA Microarrays | Enables the simultaneous detection of multiple resistance genes, including AmpC, offering a high-throughput molecular approach | X | |
DNA sequencing | Involves sequencing the AmpC gene to identify specific mutations or variations linked to increased expression | X | |
Whole Genome Sequencing (WGS) | Offers a comprehensive analysis of the entire bacterial genome, enabling the identification of ESBLs and other resistance mechanisms | X | |
Proteomics | Matrix-Assisted Laser Desorption/Ionisation Time-of-Flight (MALDI-TOF) | Allows for identification of bacterial species and can detect the most actively expressed ESBL and AmpC beta-lactamases in multi-drug-resistant (MDR) gram-negative Enterobacteriaceae e.g. MALDI Biotyper® MBT STAR-Cepha assay, Bruker | X |
Biochemical | Chromogenic Agar | Incorporates specific substrates that change colour in the presence of ESBLs including most of those carrying AmpC type resistance e.g. CHROMagar™ ESBL, CHROMagar | X |
Immunological | Enzyme-Linked Immunosorbent Assay (ELISA) | Utilizes antibodies to detect AmpC, providing a rapid and specific immunological confirmation | X |
Automated | Automated systems | Automated platforms for bacterial identification and susceptibility testing, including AmpC detection e.g. VITEK 2, MicroScan, and Phoenix | X |
