Anti-tuberculosis drug susceptibility testing of Mycobacterium bovis BCG Tokyo strain

SETTING: The Mycobacterium bovis bacille Calmette-Guérin (BCG) vaccine is the only vaccine against tuberculosis (TB), owing to its valuable protective effects and low virulence. However, it can occasionally cause systemic infection in immunocompromised hosts. Isoniazid (LNH), rifampicin (RMP), streptomycin (SM) and ethambutol (EMB) are known to be effective anti-tuberculosis drugs and are used for the treatment of BCG infections. Unfortunately, there are few studies of the susceptibility of BCG vaccine strains to these drugs. OBJECTIVE: To measure the minimum inhibitory concentrations (MICs) of BCG Tokyo vaccine products for anti-tuberculosis drugs and assess vaccine safety in terms of drug susceptibility. DESIGN: We measured the MIC for one seed and five product lots of BCG Tokyo strain for INH, RMP, SM and EMB using Middlebrook 7H11 agar plates. RESULTS: The MIC results for INH were 0.06 and 0.125 μg/ml for the product and seed lots, respectively. The MIC results for RMP, SM and EMB were 0.25-0.5, 0.25 and 2-4 μg/ml, respectively. CONCLUSION: Our results indicate that the BCG Tokyo strain was susceptible to the major anti-tuberculosis drugs and treatable even in cases of severe adverse events, including systemic infection.