Efficacy of Gratiola officinalis L. (Scrophulariaceae) Extract Against Multidrug-Resistant Mycobacterium tuberculosis in Vitro

This study aimed to evaluate the efficacy of a dry extract solution of Gratiola officinalis L. against reference and clinical strains of M. tuberculosis, including multidrug-resistant (MDR) strains. Material and Methods — The extract of Gratiola officinalis L. was prepared using the authors’ original technique. Its effects were assessed in vitro against a reference strain of M. tuberculosis that was clinically sensitive, a clinical MDR M. tuberculosis strain (with nucleotide substitutions in codon 531 of the rpoB gene [rifampicin resistance] and codon 315 of the katG gene [isoniazid resistance]), and additional sensitive and reference strains. Results — Minimum inhibitory concentrations (MICs) of the Gratiola officinalis L. extract were determined. At 14 mg/mL, the extract exerted a complete bactericidal effect against the M. tuberculosis reference strain. At 26.6 mg/mL, growth of the clinically sensitive M. tuberculosis strain (sensitive to isoniazid, rifampicin, ethambutol, and streptomycin) was fully suppressed. At 53.1 mg/mL, growth of the MDR M. tuberculosis strain (resistant to rifampicin, isoniazid, streptomycin, and ethambutol) was fully suppressed. Conclusion — The Gratiola officinalis L. extract demonstrated high bacteriostatic and bactericidal activity against Mycobacterium tuberculosis. This activity was evident against a reference strain (assessed via colony growth dynamics) and, using the serial dilution method, against a sensitive clinical strain and an MDR strain resistant to isoniazid and rifampicin.