Background: Preclinical therapeutic efficacy of new anti-TB molecules is normally
assessed by examining reduction in the bacterial load in different organs of mice infected with
M. tuberculosis. However, since infection in the peripheral blood can mirror overall bacillary load in
the body, assessment of bacteremia may reflect the treatment outcome in a more reliable manner
while obviating the need to examine different organs.
Objective: This study was aimed at determining the effect of anti-TB drugs on bacteremia in mice
infected with M. tuberculosis
Methods: BALB/c mice were intravenously infected with M. tuberculosis
and effect of oral
treatment with Isoniazid (INH) and Rifampicin (RFM) on bacilli present in the peripheral blood,
lungs, spleen and liver was determined. Colony forming units (CFUs) were enumerated by plating
the lysed blood sediments or tissue homogenates, onto Middlebrook 7H11 agar. Drug efficacy was
assessed as log reduction in CFUs in different tissues.
Results: A progressive increase in M. tuberculosis CFUs was seen in the blood of untreated mice.
Upon treatment with INH and RFM, respectively, 1.77 and 1.97 log reductions in blood CFUs were
seen. Multiplication and killing (after drug treatment) of M. tuberculosis
in the blood and other
tissues of mice were comparable.
Conclusion: Determination of M. tuberculosis
CFUs in the blood of mice can serve as a simple and
efficient method for primary selection of in vivo