ABSTRACT
We tested isolates of Mycobacterium tuberculosis recovered from 117 patients for their susceptibilities to isoniazid (INH) and rifampin (RIF) by the Centers for Disease Control and Prevention's disk modification of the indirect method of proportions (MOP) test and a three-tube mycobacteria growth indicator tube (MGIT; BBL) antimycobacterial susceptibility test (AST). Sixty-seven of the M. tuberculosis isolates were recovered from Lowenstein-Jensen (BBL) subcultures, and 50 of the isolates were recovered from MGIT cultures of samples from various body sites. For the MGIT AST method, 0.5 ml of test organism suspension was inoculated into an MGIT with 0.1 micrograms of INH per ml, an MGIT with 1.0 micrograms of RIF per ml, and growth control MGIT. The tubes were incubated at 37 degrees C and were examined daily. The MGIT AST results were interpreted as follows: susceptible if the tubes containing INH or RIF did not fluoresce within 2 days of the time that the positive growth control fluoresced and resistant if the tubes containing INH or RIF did fluoresce within 2 days of the time that the positive growth control fluoresced. The mean time fluorescence for the positive growth control was 5.5 days. The two methods were in agreement for 114 of the 117 isolates from patients, while for 3 isolates there were minor discordant results.
Subject(s)
Antitubercular Agents/pharmacology , Isoniazid/pharmacology , Microbial Sensitivity Tests/methods , Mycobacterium tuberculosis/drug effects , Rifampin/pharmacology , Antibiotics, Antitubercular/pharmacology , Drug Resistance, Multiple , Evaluation Studies as Topic , Humans , Mycobacterium tuberculosis/growth & development , Mycobacterium tuberculosis/isolation & purificationABSTRACT
Five hundred five blood samples for culture were processed in the Isolator lysis-centrifugation system and were then inoculated into a Mycobacteria Growth Indicator Tube (MGIT) and onto a Lowenstein-Jensen (L-J) slant. Forty-nine isolates of Mycobacterium avium complex and three isolates of Mycobacterium tuberculosis were recovered from 50 of the blood culture specimens. Forty-five isolates from 43 specimens were recovered in the MGIT, with a mean time to detection of 21 days. Forty-one isolates from 40 specimens were recovered in the L-J slants, and the mean time to detection was 36 days. Nine specimens were positive in the MGIT alone, while seven specimens were positive only in L-J medium.
