The effect of ozone and open air factor on environmental microbial isolates of significance in the food industry

Abstract

Ozone and open air factor (OAF) have been reported in the research literature as being effective anti-microbial agents. The action of ozone on microbes is relatively well understood, but the action of OAF is not well characterised. Both ozone and OAF have relatively short half-lives and do not leave behind toxic residues. The advantages of using a gas instead of aerosols, or droplets produced by fogging to decontaminate surfaces, is that a gas will come into contact with the horizontal, vertical and inverted planes of the surfaces (by diffusion), whereas aerosols or droplets will be affected by gravity. The effect of gaseous ozone, OAF and ozonated water with or without d-limonene emulsified in alcohol on surface attached and biofilm environmental L. monocytogenes amd P. aeruginosa were investigated. The interaction of each treatment with microorganisms was elucidated by determining microbial survival on different food contact surfaces, detecting cell injury by examining treated environmental L. monocytogenes cells using scanning electron and atomic force microscopy. All treatments were significantly more effective in eliminating the gram negative than the gram positive bacteria. This may be due to differences in cell wall structure and the cell’s ability to produce extracellular polymeric substances. Scanning electron microscopy revealed that gaseous ozone caused the cells to bleb out their cellular contents, whereas for OAF treated cells, holes were apparent in the cell wall. The ozonated water treatments were more effective in stripping the biofilm away from the surface substrata. The atomic force microscope showed that OAF, ozonated water and terpene, and the terpene in water treatments caused visible cell surface property changes, compared to gaseous ozone and ozonated water treatment alone.