Standardization of susceptibility testing methods

Standardization of antibiotic susceptibility tests is desirable but faces several problems. Despite considerable effort, it has been impossible to devise an ideal medium, and discussion continues as to the best inoculum, disk content, atmosphere of incubation, method of reading results, and interpretation of those results in both microbiological and clinical contexts. A range of methods, from manual to almost completely automated, is in current use. Some microbiologists, especially those who use NCCLS methods, advocate the universal adoption of one method for each type of manual test - agar dilution, broth dilution or agar diffusion. Others accept diversity, believing that strict adherence to protocols will make it possible for the results obtained by one method - though not necessarily their interpretation - to be superimposed on those obtained by other methods.