infectious diseases
Susceptibility Testing
Introduction
Susceptibility tests determine a microbe’s vulnerability to antimicrobial drugs by exposing a standardized concentration of organism to specific concentrations of antimicrobial drugs. Susceptibility testing can be done for bacteria, fungi, and viruses. For some organisms, results obtained with one drug predict results with similar drugs. Thus, not all potentially useful drugs are tested. Susceptibility testing occurs in vitro and may not account for many in vivo factors (eg, pharmacodynamics and pharmacokinetics, site-specific drug concentrations, host immune status, site-specific host defenses) that influence treatment success. Thus, susceptibility test results do not always predict treatment outcome. Susceptibility testing can be done qualitatively, semiquantitatively, or using nucleic acid–based methods. Testing can also determine the effect of combining different antimicrobials (synergy testing). 