Current and Emerging Methods of Antibiotic Susceptibility Testing

Abstract

Antibiotic susceptibility testing (AST) specifies effective antibiotic dosage and formulates a profile of empirical therapy for the proper management of an individual patient's health against deadly infections. Therefore, rapid diagnostic plays a pivotal role in the treatment of bacterial infection. In this article, the authors review the socio-economic burden and emergence of antibiotic resistance. An overview of the phenotypic, genotypic, and emerging techniques for AST has been provided and discussed, highlighting the advantages and limitations of each. The historical perspective on conventional methods that have paved the way for modern AST like disk diffusion, Epsilometer test (Etest), and microdilution, is presented. Several emerging methods, such as microfluidic-based optical and electrochemical AST have been critically evaluated. Finally, the challenges related with AST and its outlook in the future are presented.

Keywords: Antibiotic susceptibility tests; bacteria; genotypic; phenotypic; resistance.

Figure 1

Representation of the final ranking of antibiotic-resistant bacteria, adapted with permission from Tacconelli et al. [11]. CR = carbapenem resistant. 3GCR = third-generation cephalosporin resistant. VR = vancomycin resistant. MR = meticillin resistant. ClaR = clarithromycin resistant. FQR = fluoroquinolone resistant. PNS = penicillin non-susceptible. AmpR = ampicillin resistant.

Figure 2

Representation of various conventional antibiotic susceptibility testing methods. (a) Disk diffusion, demonstrating of inhibition zones, adapted from Sageerabanoo [29]. (b) Etest gradient disk diffusion, adapted from Sader [30], under terms of the Creative Commons attribution license. (c,d) Broth macro and micro dilution, showing bacterial susceptibility based on optical density and (e) Matrix-Assisted Laser Desorption Ionization-Time of Flight Mass Spectrometry (MADI-TOF MS), adapted from the MALDI Biotyper system (Bruker, Billerica, Massachusetts, United States), Laboratory Information System (LIS) and Laboratory Information Management System (LIMS).

Figure 3

Digital PCR-High Resolution Melt analysis (HRM)-based bacterial identification from mixed bacterial samples, reproduced with permission from [71], published by American Chemical Society, 2017. (SVM: Support-vector machine)

Figure 4

Demonstration of sensors for antibacterial susceptibility testing involving (a) an optical microfluidics biosensor, showing optical detection of microbial cultures, reproduced with permission from [83], published by RCS Advances, 2015; and (b) an electrochemical biosensor, detection was based on hybridization of the target bacterial 16S rRNA with a detector probe, adapted with permission from Liu [86] (under terms of the Creative Commons attribution license).