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Bacterial pathogens such as Escherichia coli are major causes of enteric and respiratory diseases in livestock and can spread within animal houses via contaminated surfaces and the air. Conventional disinfection is usually carried out only in empty animal houses between production cycles; therefore, the microbial load cannot be reduced while animals are present. Chlorine dioxide (ClO₂) is an established disinfectant used in drinking water treatment and the food industry, and in livestock production mainly for water-line sanitation and the disinfection of empty animal houses. It is a selective oxidising agent that inactivates microorganisms mainly by oxidising amino acid residues in proteins and is effective at low concentrations. As a gas or aerosol, it may therefore be suitable for reducing microbial contamination in animal houses while animals are present.

The aim of our study was to evaluate the antibacterial efficacy of low concentrations of airborne ClO₂ against E. coli under controlled conditions.

The experiments were carried out in a sealed glove-box exposure chamber of approximately 1 m³, equipped with an electrochemical ClO₂ sensor, a temperature and humidity sensor, and a fan to ensure homogeneous gas distribution. A 600 ppm ClO₂ test solution was sprayed into the chamber, and the airborne ClO₂ concentration was monitored continuously. An in-house E. coli strain (30037) was cultured in BHI broth at 37°C for 24 h. Two sample types were exposed in open Petri dishes: 100 µl of bacterial suspension (10⁵ CFU/ml in PBS) placed on the surface of empty Petri dishes, and bacteria spread on agar plates. Samples were exposed to 1, 3, and 6 ppm ClO₂ for 20 min at 25°C and 98% relative humidity; unexposed samples served as controls. After incubation at 37°C, surviving bacteria in the PBS samples were quantified by colony counting, while bacterial growth on agar plates was evaluated semi-quantitatively. In a complementary suspension experiment, E. coli suspended in PBS was directly treated with 1 ppm ClO₂.

Exposure to airborne ClO₂ at 1 and 3 ppm for 20 min did not result in a detectable reduction in viable E. coli counts compared with the controls. In contrast, exposure to 6 ppm ClO₂ resulted in an approximately 3-log₁₀ reduction in viable bacterial counts. In the suspension experiment, direct exposure to 1 ppm ClO₂ reduced the viable bacterial concentration from 5.5 × 10⁵ CFU/ml to below the detection limit (<10 CFU/ml), corresponding to a reduction of >4.75 log₁₀.

These results demonstrate that airborne ClO₂ can substantially reduce E. coli viability under controlled conditions, although considerably higher concentrations are required for airborne exposure than for direct treatment in suspension. Further studies are needed to determine the concentration–exposure time relationship and to evaluate the efficacy and safety of airborne ClO₂ under conditions representative of occupied animal houses.