False resistance to imipenem with a microdilution susceptibility testing system

Routine monitoring of antibiotic resistance at Children's Hospital, Boston, detected a dramatic increase in the prevalence of imipenem-resistant strains of Pseudomonas aeruginosa. Further studies documented that false resistance to imipenem was due, in part, to the loss of imipenem potency in customized MIC microdilution trays supplied by Sensititre Ltd. (West Sussex, United Kingdom). Recognition of the problem was delayed by use of the quality control standard recommended by the manufacturer, which were higher and broader than those suggested by the National Committee for Clinical Laboratory Standards.