The ESP culture system for drug susceptibilities of Mycobacterium avium complex

Objective To validate the non-radiometric, broth-based ESP system for deter mining Mycobacterium avium complex (MAC) susceptibilities. Methods MAC: isolates fi om sterile body sites of 20 adult HIV-infected pat ients who ware failing their present MAC regimen were identified. Susceptib ilities were determined and comparisons made between the agar proportion me thod and the ESP system for clarithromycin, ethambutol, sparfloxacin and cy closerine. Results Ninety-nine percent of the MICs generated by the ESP system were id entical to or lower than the MICs determined by the agar proportion method. In vitro resistance was documented by the ESP system for 86% of the drugs that patients were taking at the time of breakthrough, and no resistance wa s seen to cycloserine, a drug that no patient was taking. Conclusions The ESP system, a East and reliable method for determining MAC susceptibilities, could be used to optimize MAC regimens in a timely fashio n, avoid the use of ineffective drugs, minimize emerging resistance and ult imately improve outcome.