Antimicrobial activity and Effects on Innate Immune Responses of Coleus Lanuginosus (Hochst. Ex Benth.) and Microglossa Pyrifolia (Lam.Kuntze.) in BALB/c Mice

Abstract

The problem of microbial drug resistance is on the rise, and many antibiotics used to treat microbial pathogens are not working well due to the emergence of resistance. New novel sources of drugs capable of tackling cases of antimicrobial resistance are urgently required. Secondary metabolites from plants are such molecules that could be exploited in managing this issue. This study evaluated the extracts of Coleus lanuginosus and Microglossa pyrifolia for their antimicrobial activity and ability to stimulate the innate immune response in BALB/C mice. The two plants were selected based on their ethnomedicinal relevance and historical use in treating infectious and inflammatory conditions. Specifically, Microglossa pyrifolia has traditionally been used in the treatment of malaria, dermal and other skin infections, while Coleus lanuginosus is commonly used for managing wound infections and upper respiratory tract infections in the Kamba community. The leaves and stems of the two plants were collected from Makueni County, processed, and then extracted using aqueous and methanolic solvents. These were then evaluated for antimicrobial activity against selected Gram-positive (Bacillus subtilis and Staphylococcus aureus) and Gram-negative (Pseudomonas aeruginosa and Escherichia coli) bacteria. In addition, antifungal testing was conducted against Candida albicans. Disc diffusion assay was employed, and the resulting zones of inhibition were measured. Minimum inhibitory concentrations (MICs) were also determined. To determine the ability of the extracts to stimulate the immune responses, BALB/C mice were utilized. The ability of the extracts to reverse pyrogallol induced immunosuppression were also determined. Total and differential WBCs were determined before treatment, after pyrogallol treatment and after treatment with extracts. Phytochemical characterization was undertaken using gas chromatography-mass spectrometry (GC-MS). The two extracts exhibited antibacterial activity against tested bacterial strains. Microglossa pyriforia leaf extract revealed higher effects among the bacterial strains tested. The extracts also showed antifungal activity against Coleus albicans. In addition, the extracts also showed minimum inhibitory concentration (MICs) activity against selected microbes ranging from 6.25mg-50mg/kg. Our results also demonstrated that the administration of Coleus lanuginosus and Microglossa pyrifolia extracts to pyrogallol-immuno compromised mice significantly (p < 0.05) enhanced percent neutrophil adhesion and increased total and differential leukocyte counts compared with the control. Data obtained from this study was analyzed using ANOVA and Tukey’s post-hoc test with the level of significance fixed at p<0.05. Compounds with identified antimicrobial and immune-enhancing properties such as Beta-Copaene, α-humulene, α-caryophyllene, Alpha-Curcumene and Phytol were identified in the extracts. No mortality or adverse toxic effects were observed in the animal models following the administration of the extracts. These findings support and validate the traditional use of Coleus lanuginosus and Microglossa pyrifolia in the treatment of infectious diseases and highlight their potential as novel antimicrobial and immune-enhancing agents. Given that leaf extracts demonstrated stronger antimicrobial and immunomodulatory activity than stem extracts, this study recommends the preferential use of leaves in herbal preparations to support both efficacy and the conservation of medicinal plant species. Future studies should further investigate the aqueous extracts and isolate the active compounds responsible for immune modulation and antimicrobial effects.