Attempted reduction of Abbott MS-2 false-susceptible errors for cefotaxime-resistant Pseudomonas aeruginosa by medium modification.

Thirty-five modifications of Abbott MS-2 growth medium were evaluated in an attempt to reduce the high frequency of false-susceptible errors produced by the MS-2 system when testing resistant Pseudomonas aeruginosa against cefotaxime. A hypotonic modification with 0.1% KNO3 reduced the errors from 41 to 20% for 23 resistant isolates. All hypertonic modifications proved unsatisfactory. No modification reduced false-susceptible errors to acceptable clinical levels.