TABLE 1.

Contamination rate and time of interpretation of a direct MTT assay for detection of rifampin-resistant M. tuberculosisa

Assay weekNo. of contaminated samples/total no. of samples tested (%)No. of interpretable samples/total no. of samples tested (%)No. of samples giving the indicated assay resultb
MTT7H10 (indirect)
SRSR
11/69 (1.4)43/68 (63)376
24/69 (5.8)64/65 (98.5)568
33/69 (4.3)66/66 (100)588
Total8/207 (3.9)69/69 (100)618618
  • a Samples were inoculated in duplicates into drug-free broth medium. The change in OD was measured with the MTT assay (1) at 1 and 2 weeks after inoculation.

  • b S, susceptible; R, resistant.