Antibiotic susceptibility testing: news and traps

Abstract

The rapid evolution of antimicrobial resistance, in particular among Gram-negative bacteria requires accurate identification of resistance mechanisms in order to guide antibiotic therapy. Hence, determination of antimicrobial susceptibility of relevant bacterial isolates is a major task of clinical microbiology laboratories. The goal is to confirm susceptibility to selected antimicrobial agents, to detect resistance, but also to provide data for empiric antibiotic therapy guidelines. Various methods are available to perform antibiograms: broth microdilution, automated methods and manual methods such as disk diffusion. All methods provide qualitative assessment using the clinical categories susceptible, intermediate or resistant and some methods can provide qualitative result (minimal inhibitory concentrations). Additionally, antibiogram is a useful tool to track changes in antimicrobial resistance, as mechanisms are too diverse to be easily detected by current molecular techniques. While rapid techniques and new automated methods that could provide faster results are under development, it seems likely that antibiogram will continue to be relevant for the years to come in the management of bacterial infections. Its appropriate interpretation, sometimes complex, underline the constant need of dialog between microbiologists and clinicians.