Antimicrobial Susceptibility Testing: A Comprehensive Review of Currently Used Methods

Abstract

Antimicrobial resistance (AMR) has emerged as a major threat to public health globally. Accurate and rapid detection of resistance to antimicrobial drugs, and subsequent appropriate antimicrobial treatment, combined with antimicrobial stewardship, are essential for controlling the emergence and spread of AMR. This article reviews common antimicrobial susceptibility testing (AST) methods and relevant issues concerning the advantages and disadvantages of each method. Although accurate, classic technologies used in clinical microbiology to profile antimicrobial susceptibility are time-consuming and relatively expensive. As a result, physicians often prescribe empirical antimicrobial therapies and broad-spectrum antibiotics. Although recently developed AST systems have shown advantages over traditional methods in terms of testing speed and the potential for providing a deeper insight into resistance mechanisms, extensive validation is required to translate these methodologies to clinical practice. With a continuous increase in antimicrobial resistance, additional efforts are needed to develop innovative, rapid, accurate, and portable diagnostic tools for AST. The wide implementation of novel devices would enable the identification of the optimal treatment approaches and the surveillance of antibiotic resistance in health, agriculture, and the environment, allowing monitoring and better tackling the emergence of AMR.

Keywords: antimicrobial resistance; antimicrobial susceptibility testing; methods.

Figure 1

Current methods for antimicrobial susceptibility testing and turnaround time (created with BioRender.com, accessed on 27 February 2022. Reproduction of this figure requires permission from BioRender.com). PCR—polymerase chain reaction. qPCR—quantitative polymerase chain reaction. NGS—next-generation sequencing. MALDI-TOF MS—matrix-assisted laser desorption/ionization time-of-flight mass spectrometry.

Figure 2

Disk diffusion and gradient test of various bacterial isolates. (A)—Antimicrobial susceptibility of Streptococcus pyogenes showing iMLS phenotype, using disk diffusion method. (B)—Antimicrobial susceptibility of extended-spectrum beta-lactamase-producing Pseudomonas aeruginosa, using disk diffusion method. (C)—Gradient test of Enterococcus spp. iMLS phenotype—inducible macrolide, lincosamide, and streptogramin phenotype.

Figure 3

The basic workflow of molecular-based techniques for antimicrobial susceptibility testing. The routes from a clinical specimen to a final result are indicated by arrows (created with BioRender.com, accessed on 27 February 2022. Reproduction of this figure requires permission from BioRender.com).