South Asian Research Journal of Natural Products

The increasing prevalence of antimicrobial resistance among pneumonia-causing bacteria has intensified the search for alternative therapeutic agents from medicinal plants. This study evaluated the antibacterial activity of Plastotoma africana extracts against selected pneumonitic bacteria and investigated the phytochemical drivers of observed activity using correlation and regression analysis. Aqueous, ethanol, and methanol leaf extracts were tested against Streptococcus pneumoniae, Staphylococcus aureus, Klebsiella pneumoniae, and Haemophilus influenzae using agar well diffusion and minimum inhibitory concentration (MIC) assays.  The methanol extract exhibited the highest antibacterial activity, with zones of inhibition ranging from 18.6 ± 0.6 mm (K. pneumoniae) to 22.1 ± 0.8 mm (S. aureus), compared to ethanol (14.2–17.5 mm) and aqueous extracts (9.6–13.1 mm). A dose-dependent response was observed, with inhibition increasing from 12.7 mm at 25 mg/mL to 22.1 mm at 100 mg/mL. MIC values for the methanol extract were 12.5 mg/mL for Gram-positive bacteria and 25 mg/mL for Gram-negative bacteria. Quantitative phytochemical analysis revealed higher concentrations of total phenols (52.4 ± 1.9 mg/g), flavonoids (41.2 ± 1.6 mg/g), and alkaloids (34.8 ± 1.3 mg/g) in the methanol extract. Strong positive correlations were observed between total phenols and antibacterial activity (r = 0.86–0.93), while regression models explained 84–89% of the variation, with total phenols emerging as the strongest predictor. These findings provide scientific validation for the ethnomedicinal use of Plastotoma africana and highlight its potential as a source of bioactive compounds for the development of alternative antipneumonitic therapeutics.