Data Report Reference Page

As a service to our suppliers, this page aids interpretation of testing sample assay data.  Please note that column references are made in reference to official TAACF data reports mailed to suppliers upon testing completion.  Browse to Screening Assays for compound requirements and test descriptions.

Primary Assay Data (Level 1)

All compounds are initially screened against Mycobacterium tuberculosis strain H37Rv at the single concentration, 6.25 µg/mL. Please note the column labeled % Inhibition. Compounds are considered active in the primary screen if, at this concentration, inhibition ³ 90%. Activity is designated by a + in the column labeled Activity. In this and all other types of data reports, a column labeled Comments may be present noting any observations, unusual considerations, or resupply needs for more advanced screening.

MIC Assay Data (Level 2)

Compounds are screened by serial dilution beginning at 6.25 µg/mL. The column labeled MIC lists the measured minimum inhibitory concentration, defined as the minimum concentration of compound required to give 99% inhibition of bacterial growth. The significance of this value depends on several factors such as compound structure, novelty, toxicity, and potential mechanism of action, though generally an MIC £1 µg/mL in a novel compound class is considered an excellent lead.

Cytotoxicity Assay Data (Level 2)

Compounds are screened by serial dilution to assess toxicity to a VERO cell line, generally beginning at 10 X the MIC if sample solubility in culture media permits. Note the column labeled SI. The selectivity index is defined as the ratio of the measured IC50 in VERO cells to the MIC described above. Generally, compounds with an MIC £ 6.25 µg/mL and an SI ³10 (occasionally lower) are moved forward.

Macrophage Assay Data (Level 3)

Selective compounds as determined in Level 2 assays are tested for efficacy in vitro in a TB-infected macrophage model. The columns labeled EC90 and EC99 list the concentrations effecting 90% and 99% reduction in residual mycobacterial growth after seven days, compared to untreated controls. Compounds with EC90 > (16 X MIC) (as reported in the column labeled EC90:MIC) are considered inactive in the model.

SDRMIC Assay Data (Level 3)

The columns labeled MIC H37Rv and MIC Erdman list confirmatory MICs against two strains of M. tuberculosis. The MIC is also determined against a panel of singly-drug-resistant strains. Generally, strains resistant to isoniazid (INH), rifampin (RMP), and thiacetazone (TAC) are used, unless the structure of the compound suggests another specific strain. The corresponding MIC values serve as further confirmation of activity. Note the columns labeled, e.g., INH-R:MIC; these values are the ratios of MICs in the resistant and non-resistant strains, and should generally be »1, though there is considerable experimental variability in MIC determinations. A ratio greater than eight between the MICs in the resistant to the non-resistant strains indicates that the strain is cross-resistant to the sample.

M. avium MIC Assay Data (Level 3)

Concurrent with the SDRMIC assay, MIC is determined against a single strain of M. avium. The report is similar to the Level 2 MIC Assay report (note the column labeled MIC). Depending upon selectivity, samples with an M. avium MIC £ 6.25 may move forward for evaluation in additional M. avium assays.

MBC Assay Data (Level 3)

The columns labeled MBC vs X show the minimum bactericidal concentration as determined in strain X of the panel. Generally, if MBC » MIC, the compound is considered bacteriostatic rather than bactericidal, and is often of reduced interest. For convenience, these ratios also appear on the report.  Ratio values greater than 16 are indicative of bacteriostatic rather than bactericidal activity.

Tuberculosis Animal Model (in vivo) Assay Data

Currently, there are two animal models available, the GKO [IFN gammo KO mice on a C57BL/6 background (Jackson)] model and a standard (C57BL/6 mouse) TB model.  In both models, drug treatment begins 20 days after inoculation of the animal with M. tuberculosis. Bacterial counts are measured on day 30 (GKO only) and days 35 and 50 (standard model) in two tissues (lung and spleen), and compared with counts from negative (untreated) controls. Compounds are considered active if they yield at least a 0.75 log10 reduction in bacterial counts, and moderately active if they afford somewhat less (~0.5 log10) protection, as noted in the column labeled Activity. Log10 protection data for both tissues are reported in the column labeled Log protection (lung/spleen), and any unusual details of the experiment are summarized in the column labeled Observations. Data from a positive control (i.e., treated with a known TB drug, typically INH) are also reported in the column labeled Control protection (lung/spleen).