Abstract
Microbiology laboratories devote a great deal of effort to the in vitroinvestigation of antibiotics. In the U.K., U.S.A. and in Australia external quality assurance programmes concern themselves with these efforts, and their conclusions have been discussed in recent papers.1,2Data are also available from the RCPA programme in microbiology. The most frequent of these investigations is the antibiotic susceptibility test, which gives us information on the in vitroactivity of an antimicrobial agent against a bacterium under standard conditions, information which experience has shown to correlate with performance in vivo. A number of methods are available for susceptibility testing (ST): agar (disc) diffusion, agar dilution, broth dilution and, recently, semi-automated techniques using machines which yield answers more rapidly than the conventional methods.
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