Our study is a pioneer in the evaluation of the antifungal action of O3 gas on the surface of culture medium contaminated by C. albicans and A. fumigatus due to: (1) the test of different distances and places using two equipment to generate this gas; (2) the assessment of air flow interference on antifungal effects.
According to the data, despite observing CFU measures, after ozonation, showed lower number than those of the control group for both experiments, considering all variables: microorganisms, distances, directions, O3 gas generator and air conditioning turned on or off.
The Mod.I device statistically showed greater efficiency in the microbial load reduction process, regardless of the fungal species tested, which is explained by the different flow of the devices. Although O3 concentrations in part per million (ppm) are virtually equal, the Mod.I O3 generator has twice as much flow when compared with Mod.II. Face to an exception of the reduction of CFU with Mod.II was observed, which had no difference in the results with statistical significance of the cultures of C. albicans at 2 m of distance, and A. fumigatus, at 1 and 2 m of distance, regardless of the place of the dishes (A, B and C). An associability or dependence between the directions and distances is proven regarding the other groups, interfering in the antifungal activity of O3 gas.
In this context, the best experimental condition occurred to C. albicans, at 30 cm of distance, direction B (central), while A. fumigatus, at 2 m of distance and direction A (dishes near the wall), represented the less favorable condition. This may be related to the gas flow rates. In laminar flows, particles move orderly, always maintaining the same relative position. In the turbulent regime, these particles move randomly and irregularly [13], that is, the flow of O3 gas when reaches the wall causes disorder, thus decreasing antifungal activity when compared with the dishes near the wall, which may have interfered with the O3 flow, thus justifying the variation in the number of CFU in all distances and directions.
The best antifungal activity in the ozonation process for both devices when the air conditioner was turned off, for both fungal species, may have been observed due to the lack of interference with the O3 flow, resulting in surfaces more affected by O3 gas. Unlike when the air conditioning was turned on, with the function of capturing air and filter before throwing it again into the environment [14], the flow of O3 gas varies when reaching the surface, thus decreasing its antifungal activity.
According to the literature, temperature, relative humidity variation and treatment time lead to a modified O3 antimicrobial effect [15]. In our study, these factors were maintained equal in all experimental conditions, minimizing possible biases. According to the values we detected, the cultures of C. albicans were more sensitive than A. fumigatus, which corroborates the literature [15]. In fact, A. fumigatus has can grow and survive humidity environments and extreme temperatures, with dispersion of conidia [9]. According to Santana et al [7], C. albicans is less adapted to the diversity of environments outside the human body than A. fumigatus.
Several studies have been conducted aiming at investigating the antimicrobial activity of O3 gas against fungi, sensitive or resistant, with different exposure time and concentrations. Variables were analyzed for yeast inhibition, germination tube formation and biofilm, proving that O3 gas in well-established protocols for exposure time always shows excellent antimicrobial activity [5, 12, 17, 18]. Thus, it is evident that our study corroborates other studies in the literature.
Zotti et al. [19] observed phenotypic changes in the colony of A. flavus and A. niger after exposure to O3 gas, with sharp decrease in growth of both fungi, and change in their natural pigmentation. In addition to the antimicrobial activity, O3 gas can be expected to inhibit pigments and protein synthesis, with future impairment to virulence factors of pathogenic fungal species.
Surface cleaning is crucial for the control of Healthcare-Associated Infections (HAI) [20]. Unfortunately, health services surface cleaning and disinfection is often overlooked. Cleaning and disinfection practices of the environment, equipment, and surfaces should be implemented and discussed by the Hospital Infection Commissions, together with nursing and cleaning services, developing activities related to environmental hygiene protocols, supervision, and training [4, 21, 22, 23, 24].
Finally, it is important the search for new products, methods, and practices for surface disinfection, and the O3 gas appears as a promising compound.
