Asian Journal of Microbiology and Biotechnology

Introduction: The rising incidence of antimicrobial resistance in Klebsiella pneumoniae has necessitated interest in the exploration plant-based antimicrobial agents. Psidium guajava (guava) leaves are used traditionally for the treatment of infectious diseases and are rich sources of bioactive compounds with antimicrobial potentials. Hence, this study was aimed at evaluating the in vitro antibacterial activity of Psidium guajava leaf extracts against clinical isolates of Klebsiella pneumoniae isolated from the nasopharynx of students of Alex Ekwueme-Federal University Ndufu Alike Ikwo, Ebonyi State, Nigeria.

Methodology: Klebsiella pneumoniae isolates were identified using standard morphological and biochemical tests. Aqueous, ethanol, and methanol leaf extracts of Psidium guajava were prepared and subjected to qualitative phytochemical screening to determine the presence of major secondary metabolites. Five (5) K. pneumoniae isolates were tested for antibacterial activity. Antibacterial activity was evaluated using the agar well diffusion method at concentrations of 200, 100, and 50 mg/ml. Ciprofloxacin was used as the positive control.

Results: The bacterial isolates exhibited typical morphological and biochemical features consistent with K. pneumoniae. Phytochemical screening revealed the presence of tannins, flavonoids, alkaloids, saponins, and steroids in all extracts, while glycosides were not detected. The leaf extracts showed concentration-dependent antibacterial activity against K. pneumoniae. Ethanol and methanol extracts produced larger inhibition zone diameters compared with the aqueous extract at all tested concentrations. The aqueous extract produced inhibition zones ranging from 8–12 mm, the ethanol extract from 10–18 mm, and the methanol extract from 11–19 mm across the tested concentrations. Ciprofloxacin showed the highest antibacterial activity with inhibition zones ranging from 22–28 mm.

Conclusion: The findings indicated that Psidium guajava leaves possess bioactive compounds with measurable antibacterial activity against Klebsiella pneumoniae. Although less potent than ciprofloxacin, the ethanol and methanol extracts showed promising inhibitory effects, suggesting that P. guajava leaves may serve as a potential source of antibacterial agents for managing infections caused by K. pneumoniae.