ACTIVITIES OF ANTIMICROBIAL AGENTS AGAINST CLINICAL ISOLATES OF MYCOBACTERIUM-HAEMOPHILUM

Mycobacterium haemophilum, first described in 1978, can cause severe i nfections of skin, respiratory tract, bone, and other organs of immuno compromised patients. There is no standardized antimicrobial susceptib ility test, and for the 27 reported cases, a variety of test methods h ave been used. This paper reports the in vitro test results for 17 iso lates of M. haemophilum recovered from 12 patients in the New York Cit y area. MICs of 16 antimicrobial agents were determined in microtiter trays containing Middlebrook 7H9 broth plus 60 muM hemin, inoculated w ith 10(6) CFU of the organism per ml and incubated at 30-degrees-C for 10 days. Ethambutol, ethionamide, tetracycline, cefoxitin, and trimet hoprim-sulfamethoxazole were inactive against initial isolates from th e 12 patients. Isoniazid was weakly active with a MIC for 50% of strai ns tested (MIC50) of 8 mug/ml and a MIC90 of > 32 mug/ml. Three quinol ones, ciprofloxacin, ofloxacin, and sparfloxacin, were moderately acti ve with MIC50s of 2 to 4 mug/ml and MIC90s of 4 to 8 mug/ml. Amikacin and clofazamine were active with MIC90s of 4 and 2 mug/ml, respectivel y. Clarithromycin was the most active macrolide with a MIC90 of less-t han-or-equal-to 0.25 mug/ml. The MIC90 of azithromycin was 8 mug/ml, a nd the MIC90 of erythromycin was 4 mug/ml. The rifamycins were active with a MIC90 of 1 mug/ml for rifampin and one of less-than-or-equal-to 0.03 mug/ml for rifabutin. For a second isolate from the skin of one patient and an isolate from an autopsy culture of the spleen of a seco nd patient, MICs of rifampin and rifabutin were > 16 mug/ml, whereas i nitial isolates were inactivated by low concentrations of the rifamyci ns. Both patients had been treated for several months with several ant imicrobial agents, including a rifamycin.