Developments in antimicrobial susceptibility testing

Abstract

Antimicrobial susceptibility testing can be carried out by diffusion, dilution and breakpoint methods. Diffusion methods remain the most commonly used routine technique whereas dilution methods are largely used for reference work or comparative studies on new agents. In many laboratories in Great Britain breakpoint methods have been adopted for some routine tests. In the USA and some other countries, automated or mechanized methods are widely used. The 'E test' is a new method for the determination of MICs, and its technical simplicity makes it suitable for use in routine clinical laboratories. Methods based on nucleic acid probes and amplification techniques have yet to make an impact on routine testing. More recently, standardization of antimicrobial susceptibility testing has been pursued internationally, with emphasis on definition of the breakpoints between categories of susceptibility. The availability of a range of reference organisms with various degrees of susceptibility and with different resistance mechanisms would be valuable in relating methods with different technical details. Computerized rule-based systems for interpretation and control are a significant development applicable to any method of antimicrobial susceptibility testing.