Comparison of the E test and a proportion dilution method for susceptibility testing of Mycobacterium kansasii.

The newly developed E test was compared with a conventional proportion dilution method for determining the sensitivity of Mycobacterium kansasii to amikacin, streptomycin, fusidic acid, rifampicin, clarithromycin, ciprofloxacin, ofloxacin, and fleroxacin. There was no more than one strain with different rating, except for ciprofloxacin. In this case, the breakpoint concentration had an unfavourable position at the top of the strip, and susceptible isolates in the dilution test were defined resistant in the E test. It is concluded that the E test is suitable for testing slowly growing mycobacteria other than tubercle bacilli, and may replace the more laborious dilution methods, particularly for testing M. kansasii.