ABSTRACT
Basic Principles of Antimicrobial Susceptibility Testing (AST) ................................................... 149 Disk Diffusion .................................................................................................................... 150 Quantitative Testing (Minimum Inhibitory Concentration. MIC) ..................................... 151
Broth Macrodilution, Microdilution, or Agar Dilution ........................................... 152 Etest® .................................................................................................................... 152
AST of Fastidious Organisms ............................................................................................. 153 AST of Anaerobes .............................................................................................................. 154 AST of Fungi ...................................................................................................................... 154 AST of Mycobacteria .......................................................................................................... 154
Susceptibility Interpretation .......................................................................................................... 155 Agar Screen Methods .................................................................................................................... 155 Molecular Methods ........................................................................................................................ 156 Quality Control .............................................................................................................................. 156 References ...................................................................................................................................... 157
The purpose of performing antimicrobial susceptibility testing (AST) is to provide in vitro data to help ensure that appropriate and adequate antimicrobial therapy is used to optimize treatment outcomes. In addition, the AST data generated daily can be statistically analyzed on an annual basis to generate an antibiogram that reects the antimicrobial susceptibility and resistance patterns of important pathogens that prevail in a particular hospital. These hospital-specic AST epidemiologic data provide valuable guidance to the clinicians for the appropriate selection of empiric therapy, prior to the availability of culture and susceptibility results that often takes 2 to 3 days. The purpose of the AST of the culture pathogen is to help clinicians correct and/or modify empiric therapy as soon as the results become available.
