Bacteria hide their resistance – a challenge for diagnostics

Transiently silent acquired antimicrobial resistance (tsaAMR) is posing a significant challenge to diagnostic susceptibility testing of bacterial isolates. Although it appears at frequencies high enough to cause therapeutic failure in infections, its frequencies are too low to be detected by standard phenotypic tests.
In our review, we provide a comprehensive understanding of tsaAMR by defining the concept in a clinically relevant context. We also illustrate the underlying molecular mechanisms in both Gram-positive and Gram-negative bacteria.

Given the continued rise of acquired AMR in bacterial pathogens, it is likely that tsaAMR will become more prevalent. We recommend the use of genotypic testing, together with conventional phenotypic methods, to accurately detect discrepancies between genotype and phenotype and reveal the presence of bacteria strains with tsaAMR.