A comparison of the Api-10M commercial microdilution system with the tube dilution and standard microdilution methods.

The susceptibilities of urinary isolates of Escherichia coli (50 strains), Klebsiella pneumoniae (15 strains) and Proteus mirabilis (15 strains) to gentamicin and ampicillin were determined and compared using the following methods: standard tube dilution, standard microdilution, commercial microdilution and disk diffusion susceptibility tests. Results of susceptibility testing performed with the Api- 10M commercial microdilution method agreed with those of the tube dilution method in 93% of the tests, but in only 70% of those obtained with the standard microdilution method; tube dilution and standard microdilution agreed in 85.6% of the cases. All three methods of MIC susceptibility testing agreed with the disk diffusion method in 100% of the tests. There was a definite tendency for the Api- 10M system to give higher MICs than the tube dilution method; the standard microdilution method tended to give lower MICs than those obtained by tube dilution and the commercial microdilution system. The Api- 10M system is a reliable, simple and accurate method since it correlates very will with the tube dilution method.