Objectives: The aim of this in vitro microbial study was to evaluate the efficacy of Calendula officinalis tincture 60% (v/v) ethanol as an antibacterial agent for in vitro Pseudomonas aeruginosa.
Methods: The standardized disk diffusion method was employed. Seven pairs of Mueller–Hinton agar plates were used; one plate was the experiment and one a control. P. aeruginosa broth cultures were grown for 24 hours. A sterile cotton swab was soaked in P. aeruginosa broth culture and then streaked evenly in 3 directions over the entire surface of the agar plates to obtain a uniform inoculum. Sterile filter paper disks (0.45-µm pore size; 5-mm diameter) were impregnated with standardized amounts of C. officinalis tincture 60% (v/v) ethanol. The first set of disks was impregnated with undiluted C. officinalis tincture 60% (v/v) ethanol, and the subsequent sets of disks were impregnated with a series of 2-fold dilutions of C. officinalis tincture 60% (v/v) ethanol. One disk from each set was aseptically placed on the inoculated agar surface of each plate. The plates were inverted and incubated at 37°C in ambient air for 24 hours, after which any presence of clear zones of inhibition were observed against a light background and the diameter of these zones was measured. The whole procedure was performed in triplicate. The mean activity of the 2 treatment groups was 6.88 and 6.69 mm, respectively.
Results: The antibacterial activity of C. officinalis tincture 60% (v/v) ethanol and the 60% ethanol control groups showed a similar pattern on in vitro P. aeruginosa. There was no statistically significant difference between the experimental and control groups (p>0.05; t-test).
Conclusion: There was no evidence to prove the efficacy of C. officinalis tincture 60% (v/v) ethanol as an antibacterial agent for in vitro P. aeruginosa.