Detecting Antimicrobial Resistance

Abstract

● To optimize antimicrobial therapy for the management of individual patient’s infection. ● For surveillance purposes, which in turn inform local/national/international clinical guidelines. ● For the management of infection control and prevention. Broadly speaking, resistance is detected by observing its phenotypic expression (activity of the candidate drug(s) against the target bacterium) or detecting the underlying genotypic determinant (resistance genes). Commonly used methods in clinical diagnostic laboratories generally fall under the ‘phenotypic’ category. These share similar traits— ease of use, reproducibility, scalability, quick turnaround of results and relative low cost of materials/reagents required. Moreover, decades of experience and fine-tuning have seen them established as methods of choice in most microbiology laboratories. Most phenotypic test methods are reliant on the use of clinical breakpoints set by national and international bodies (e.g. EUCAST and CLSI) to determine susceptibility/resistance. These guidelines are regularly subject to updates with input from leading experts and latest research findings. It is important for clinical diagnostic laboratories to adhere to best practice guidance set out by these bodies and keep up-to-date with the latest guidelines. Growth characteristics (on artificial media) of the bacterium of interest are extremely important in conventional phenotypic methods. As this presents a big obstacle for slow growers and ‘unculturable’ pathogens (e.g. Mycobacterium tuberculosis, Mycoplasma spp.) it has led to the introduction of genotypic methods of resistance detection in the clinical diagnostic laboratory. meteoric rise in the world of microbiology. Compared with conventional phenotypic methods, molecular genotypic-based tests are better suited for automation and reduce dependence on skilled workers for result interpretation. They therefore deliver the rapid turnaround demanded by modern medicine. Antimicrobial susceptibility tests (ASTs) is a term used to describe a range of phenotypic methods that employ direct observation of the action of antimicrobials against a target microorganism. This is the most commonly used method in clinical diagnostic laboratories for detecting resistance in bacteria. A. Disc diffusion Growth medium: Standardized agar plates (usually unsupplemented, but addition(s) may be necessary for bacteria with specific growth requirements). Antibacterial component: Fixed dose in standard size circular paper discs or tablets.