In vitro antibacterial activity of mixed Garcinia buchananii B. and Curcuma longa L. ethanolic extracts against Streptococcus pneumoniae

Streptococcus pneumoniae is the main bacterial cause of community-acquired pneumonia. In children, 22% of the deaths are due to pneumonia as the single leading cause of death. The local people in Uganda use herbs like Curcuma longa Linnaeus and Garcinia buchananii Baker to manage upper respiratory tract infections (URTIs). The ethanolic extracts of the C. longa rhizome and G. buchananii stem bark have individually demonstrated antimicrobial activity against bacteria, protozoa, and viruses. Crude extracts of C. longa rhizome powder and G. buchananii fresh back were obtained through maceration using ethanol. In vitro disc diffusion method and serial dilution method were used to determine antibacterial susceptibility and minimum inhibitory concentration (MIC), respectively of the plant extracts against S. pneumoniae. Both ethanolic extracts of C. longa rhizome and G. buchananii stem bark individually showed activity against S. pneumoniae and this antibacterial effect was largely dose-dependent. However, ceftriaxone had superior antibacterial activity (p< 0.0001) than all the individual extracts and combinations. The MICs of C. longa and G. buchananii ethanolic extracts were 3.125 and 1.5625 mg/mL, respectively. The 50:50 C. longa - G. buchananii combination showed superior activity compared to other combinations, though it was not statistically significant (p > 0.05). The Fractional Inhibitory Concentration Index (FICI) was 11.68. This study concluded that the ethanolic extracts of both the rhizome of C. longa and the stem bark of G. buchananii, when used singly and in combination, demonstrated antibacterial activity against S. pneumoniae. However, the combination of the ethanolic extracts of these two plants demonstrates antagonistic activity. Key words: Curcuma longa, Garcinia buchananii, Streptococcus pneumoniae, combined antibacterial activity.