Evaluation of the MS-2 automated antimicrobial susceptibility testing system: report of a European collaborative study.

The MS-2 is an instrument for rapid automated testing of antimicrobial susceptibility. Its performance was evaluated by comparison with disc diffusion and MIC tests in a collaborative study in four European laboratories. Tests on independently isolated organisms showed the MS-2 to be in essential agreement with conventional methods in 94.8% of tests. A further series of 170 well-defined pathogens for which a reference antibiogram was available were tested by MS-2 and the manual methods in all of the participating laboratories. MS-2 results were in full accord in 90% of tests and in essential agreement in 94%. MS-2 results compared at least as well with the reference values as did either of the manual methods. Initial problems of false susceptibility results with erythromycin and penicillin were resolved by (1) the addition of small amounts of erythromycin which acted as an inducer and (2) by the use of a low content penicillin disc. MS-2 was found to be reliable and needed no attention following loading of the test cuvette cartridges. A print-out of the results was available 2-5 h after inception of the test.