Comparison of MB/BacT system and agar proportion method in drug susceptibility testing of Mycobacterium tuberculosis.

The drug susceptibilities of 105 isolates/strains of Mycobacterium tuberculosis (101 clinical isolates and four control strains from the American Type Culture Collection) were assessed by the MB/BacT system and conventional agar proportion method. The agreement rates between the two methods were 99.0% for streptomycin, 95.2% for isoniazid and 100% for rifampin. The mean times to detection for drug-resistant isolates were 4.7 days (range: 2.5-13.7 days) using the MB/BacT system and 14.8 days (range: 14-21 days) using the agar proportion method. For drug-susceptible isolates, the times to detection were 10.8 days (mean) and 21 days respectively. Thus, these data have demonstrated that the automated, non-radiometric MB/BacT system is an efficient, accurate and reliable method for assessing drug susceptibilities of M. tuberculosis compared with the conventional agar proportion method.

Antimicrobial activity of ofloxacin and other agents against mycobacterial isolates from postoperative sternotomy wounds.

In 1987 and 1988, 16 patients in a cardiothoracic hospital developed median sternotomy wound infections from Mycobacterium fortuitum or Mycobacterium chelonei (M fortuitum, 14 patients; M chelonei, two patients). For M fortuitum isolates, the minimum inhibitory concentration (MIC) (by agar dilution) of ofloxacin was 0.32 to 1.25 mg/L; of amikacin, 0.5 to 1 mg/L; of sulfadiazine, 16 to 256 mg/L; of imipenem, less than or equal to 2 to 4 mg/L; of cefoxitin, 4 to 16 mg/L; of ampicillin, 64 to greater than 256 mg/L; of cephapirin, 64 to 128 mg/L; of cefoperazone, greater than 256 mg/L; and of ceftazidime, greater than 256 mg/L. Addition of sulbactam to ampicillin and cefoperazone resulted in at least a four- to eight-fold reduction of their respective MICs. For M chelonei isolates, the MIC of ofloxacin was greater than 20 mg/L; of amikacin, 8 mg/L; of sulfadiazine, 64 mg/L; of imipenem, 8 mg/L; of cefoxitin, 16 mg/L; of ampicillin, 128 mg/L; of cephapirin, 128 mg/L; of cefoperazone, greater than 256 mg/L; and of ceftazidime, greater than 256 mg/L. Addition of sulbactam resulted in much smaller reductions of the MICs of ampicillin and cefoperazone. Synergism was noticed between ofloxacin and amikacin against M chelonei but not against M fortuitum. The results indicate that ofloxacin alone is as effective as the combination of ofloxacin and amikacin in treating M fortuitum, but not M chelonei, infection.

Minimal bactericidal and inhibitory concentrations of ofloxacin on Mycobacterium fortuitum at pH 7 and 5: therapeutic implications.

Mycobacterium fortuitum infections of sternotomy wounds have been successfully treated with ofloxacin, a fluoroquinolone. We studied the MBCs and MICs in vitro of this antibiotic on the organism under neutral pH (7) and acidic pH (5) and found marked escalation of these values under the latter condition. This provides hints on the therapy of these infections under in vivo settings.