Abstract
Background: Antibiotic resistance, persistent cells in respiratory infections, and adverse effects associated with antibiotics underscore the urgent need to search for alternative treatments. Natural products such as essential oils derived from aromatic plants like Callistemon citrinus may be a promising avenue to explore. This study aimed to assess the antibacterial activity of C. citrinus essential oils from two Cameroonian regions against bacteria causing respiratory infections, investigate their possible modes of action, and evaluate the microbiological effects of continuous exposure at sub-inhibitory concentrations.
Methods: The antibacterial activity was determined by the broth microdilution method. Potential modes of action were investigated using assays to assess effects on the bacterial membrane, protein synthesis, and H+-ATPase pump activity. Continuous exposure experiments were performed for 08 days and compared with levofloxacin as a reference.
Results: Callistemon citrinus essential oil from the University of Dschang campus exhibited the strongest antibacterial activity, with minimum inhibitory concentration values ranging from 78.13 to 468.75 µg/mL. Tests on the mode of action revealed inhibition of protein synthesis in Pseudomonas aeruginosa and interference with H+-ATPase pump activity in Staphylococcus aureus, with no significant impact on the bacterial membrane. It is noteworthy that continuous exposure to C. citrinus essential oil did not induce resistance or persistence, unlike levofloxacin, which led to the emergence of resistant and persistent populations in P. aeruginosa and S. aureus, respectively.
Conclusion: C. citrinus essential oil exhibits potent antibacterial activity against major respiratory pathogens through various cellular targets, while minimizing the risk of resistance or persistence. These results highlight its potential as a natural candidate for the development of alternative therapies; however, further studies such as chemical characterization, cytotoxicity, and in vivo validation are needed.
Keywords: Callistemon citrinus; essential oil; antibacterial; respiratory infections.
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