Antibacterial Activities of Methanol Extracts of Carica papaya, Ocimum gratissimum and Solanum torvum under Normal and Osmotic Stress Conditions

Background: Infectious diseases remain major threat to human health worldwide despite the availability of antibiotic library in drug stores, because of the emergence of new multi-drug resistant bacteria. Therefore, the discovery of new effective treatment will help in fighting such infections.

Aim: This study aimed at evaluating the antibacterial activities of extracts from three Cameroonian medicinal plants as well as the effect of osmotic stress on these activities.

Methods: Antibacterial properties of the methanol extracts of Carica papaya, Ocimum gratissimum and Solanum torvum were studied against five Gram positive and four Gram negative bacteria under normal and osmotic stress conditions. The phytochemical analysis of these plant extracts was carried out using standard methods. Broth microdilution method was used to assess the antibacterial activities of extracts as well as the effect of stress osmotic (5% NaCl) on these activities.

Results: The phytochemical analysis revealed the presence of alkaloids, polyphenols, tannins and triterpenes in all tested plant extracts. Flavonoids, anthraquinones, anthocyanins, steroids and saponins were selectively distributed in the extracts. The extract of C. papaya (MIC = 128 - 1024 μg/ml) was the most active followed in decreasing order by O. gratissimum extract (MIC = 512 - 1024 μg/ml), S. torvum leaf extract (MIC = 256 - 2048 μg/ml), and S. torvum fruit extract (MIC = 2048 μg/ml). The antibacterial activities of plant extracts and chloramphenicol increased under osmotic stress conditions while those of amoxicillin decreased under these conditions.

Conclusion: The overall results of this study provide scientific evidence of the antibacterial activity of methanol extracts of tested plants, therefore supporting their traditional use in the wound healing and infected diseases.