Synergistic antimycobacterial activity of Piper longum and Cressa cretica extracts and their effects on the expression of rpoB, gyrA and gyrB genes in Mycobacterium tuberculosis

Tuberculosis (TB) remains one of the leading causes of mortality from infectious diseases worldwide, with the increasing prevalence of multidrug‑resistant TB posing a major challenge to effective disease control. Combination therapy has become a key strategy for improving treatment efficacy, while minimizing the emergence of drug resistance. In the present study, the synergistic antimycobacterial activity of methanolic extracts of Piper longum (P. longum) and Cressa cretica (C. cretica) against Mycobacterium tuberculosis (M. tuberculosis; H37Rv) was investigated using a two‑dimensional checkerboard assay. In addition, the effects of the individual extracts on the expression of the rpoB, gyrA and gyrB genes, which are associated with transcription and DNA replication, were evaluated using reverse transcription‑quantitative PCR (RT‑qPCR). The minimum inhibitory concentrations (MICs) of P. longum and C. cretica were 125 and 250 µg/ml, respectively. When used in combination, the MIC of P. longum decreased to 7 µg/ml, while that of C. cretica decreased to 10 µg/ml, corresponding to 18‑ and 25‑fold reductions, respectively. The combination exhibited potent synergistic activity with a fractional inhibitory concentration index of 0.096. Phytochemical screening revealed the presence of several bioactive constituents, including alkaloids, phenolic compounds, flavonoids, tannins, terpenoids, glycosides, sterols, carbohydrates and proteins. RT‑qPCR demonstrated that treatment with the plant extracts altered the expression profiles of rpoB, gyrA and gyrB during different stages of bacterial growth, with the most prominent transcriptional changes were observed between 24 and 72 h following treatment. On the whole, these findings demonstrate that P. longum and C. cretica exhibit significant synergistic antimycobacterial activity against M. tuberculosis and influence the expression of genes involved in essential cellular processes. Further bioactivity‑guided fractionation, the identification of active phytochemicals, mechanistic investigations, cytotoxicity evaluation and in vivo studies are required to validate their potential as complementary therapeutic candidates for tuberculosis.