Antimicrobial effect of chamomile-containing over-the-counter ear and eye drops

Abstract

Chamomile ( Matricaria chamomilla) is a plant with known antimicrobial, anti-inflammatory, and analgesic properties. Homeopathic drops containing chamomile extract are often used for ear pain and chronic ear infections. We aimed to evaluate the antimicrobial effect of over-the-counter eardrops containing chamomile against organisms causing bacterial conjunctivitis and otitis externa. Liquid cultures of Streptococcus aureus and Pseudomonas aeruginosa were exposed to increasing concentrations of eardrops containing chamomile extract. Liquid cultures of S. aureus and Streptococcus pneumoniae were exposed to increasing concentrations of chamomile eye drops for 5, 10, 15, and 45 min. Colony forming units (CFUs) were assessed after 18 h. Viability assays for these organisms were performed using the resazurin microdilution assay. We observed a reduction in the number of P. aeruginosa CFUs when the bacteria were exposed to any of the three concentrations of the chamomile drops as early as 5 min, with maximal reduction upon exposure to the 30% concentration at 45 min. Reduction in S. aureus CFUs, on the other hand, was observed for all three concentrations as maximal in the 5 min of exposure. We observed a marked reduction in the number of S. aureus CFUs upon exposure to any of the three preparations of chamomile-containing eye drops, which was almost immediate at 10% concentration. Streptococcus pneumoniae reduction happened at 5 min and continued through the 45-min observation period for all three concentrations. Our findings suggest that over-the-counter ear drops containing chamomile extract could potentially be used as a non-prescription treatment for mild cases of otitis externa and bacterial conjunctivitis.