The Antimicrobial Susceptibility Test: A Comparison of the Results of Four Methods

A comparison of the results of the antimicrobial susceptibility tests by the agar-dilution method, the agar-diffusion method, the Autobac-1 system and the MS2 system has been made in a number of Escherichia coli and Staphylococcus aureus strains. With the agar-dilution method as a reference the agar-diffusion method and the MS2 system showed mostly satisfactory scores. With the Autobac-1 system, Esch. coli strains gave several insufficient scores with some antibiotics. A study of the distribution of minimal inhibitory concentrations against the strains has enabled the explanation of some of the discrepancies that were observed. Furthermore, the influence of two different sets of interpretive criteria on the outcome of the results has been studied.