Ozone has microbicidal activity, promoting the inactivation of microorganisms by oxidation in topical ozone therapy formulations, using gas, water, and ozonized oil as vehicles. Ozonized topical formulations have been described as adjunct therapies for the treatment of skin lesions (1–3). The objective of the study was to evaluate the in vitro microbicidal effect of these formulations applied to seven standard bacterial strains.

The antibacterial activity of ozone in vegetable oil, gas, and water formulations was evaluated against seven ATCC® and NCTC® standard bacterial strains, two multidrug-resistant Gram-negative strains: Klebsiella pneumoniae TEM, SHV®, TM KPC-2–producing, imipenem-resistant – ATCCBAA, and Escherichia coli IMP ATCC® 13476, and one Gram-positive coccus with the mecA gene (Staphylococcus aureus MRSA NCTC® 12493), and four bacterial strains non-resistant to antimicrobials (Klebsiella pneumoniae NCTC® 13368, Escherichia coli ATCC® 25922, Pseudomonas aeruginosa ATCC® 27853, and Staphylococcus aureus ATCC® 25923). Visual comparison and colony-forming unit counts on the plates were performed after exposure to ozonized formulations at different concentrations and times. Sunflower oil with a peroxide index of 600 mmol-Eq/kg was used. Gas was obtained through a medical ozone generator at concentrations of 30 and 60 mg/L. The water used was laboratory type II reagent water, with a temperature variation of 2 to 4°C, and ozonized using a medical generator. Exposure time to the different formulations ranged from 1 to 15 minutes.

After analysis, the gas and oil formulations demonstrated antimicrobial activity, inhibiting the growth of bacteria, whether multidrug-resistant or not. Ozonized water showed faster activity in inhibiting bacterial growth, followed by gas and oil formulations. In the evaluation of exposure time, 100% inhibition of strain growth was observed with all three formulations after 10 minutes.

The three topical formulations demonstrated similar in vitro antimicrobial activity, even in multidrug-resistant strains, showing potential as an adjunct topical solution for the control of these microorganisms.