Molecular Susceptibility Testing Versus Traditional Methods: An Issue of VRSAtility
Antimicrobial susceptibility testing of clinically relevant bacterial and viral isolates is of
critical importance in the treatment of serious infection. The main objective is to predict
response to appropriate antimicrobial therapy. Conventional phenotypic antimicrobial
susceptibility testing (AST) methods include broth microdilution, disk diffusion,
antibiotic gradient and agar dilution – some of which are available in automated format.
Increasingly, molecular tests to detect known genetic resistance markers (chromosomal
or plasmid-mediated) are being developed in the hope that they will offer more rapid
turnaround of AST results with increased sensitivity of detection. There are both
practical and theoretical considerations regarding the implementation of these molecular
tests that should be considered. These considerations include the lack of expression of
resistance genes, contamination with mixed or normal flora, mutations in target
sequences, and the emergence of novel resistance genes. These issues will be discussed
during the course of this presentation.