Effects on Bacteria and Viruses

Effects on bacterial aerosols (Fine: Uniform)

Aerosols were produced by spraying bacterial suspensions at 20 lb/sq. in pressure and concentrations of bacteria were in the range of 50-500 viable organisms per Eter of air. The killing effect of ozone was determined by comparing the curves for decay with, and without, ozone. Ozone concentrations ranged from 2.0 p.p.rnv. down to 0.025 p.p.mv. Tests were performed on three organisms; Streptococcus salivarius, Streptococcus'C'and Staphylococcus albus. The role of humidity in the action of ozone, particularly when the gas is at low concentration, was apparent. At humidities less than 45%, ozone, even in high concentrations, exerts no appreciable disinfecting action on bacteria. For humidities above 50%, however, ozone reduced the bacteria count. In fact, ozone as low as 0.025 p.p.m.v. showed definite bactericidal action at 60 to 80% humidity.

Bacteria that have settled on surfaces

Bacteria on surfaces constitute a potential infection danger as a source of infection through redispersal in the air or contact with skin or clothes. Tests were made to determine whether ozone has any disinfecting action on deposited bacteria. Bacteria were sprayed on various surfaces: agar in Petri dishes; Whatman filter paper; sterile glass Petri dishes and wool cloth. These were placed in known conditions of humidity (range 60-85%), temperature and ozone concentration. After being exposed. the bacteria were counted and compared with surfaces having bacteria not exposed to ozone. Ozone in a concentration of 0.02 p.p.n-Lv. in a moderately humid atmosphere exercises a very definite killing effect against bacteria on surfaces, but below this level it has little effect.

The kill depends on (a) the "depth" and type of surface; so moist agar. Whatman #1 filter paper and wool cloth are more favorable to survival than glass or #50 Whatman paper; (b) resistance to ozone of different types of bacteria: Staphylococcus albus resistance is greater than Streptococcus Salivaiius, which in turn is greater than B.prodigiosus.

Discussion

Ozone, in concentrations up to 0.04 p.p.m.v. in humid atmospheres exerts a disinfecting action on certain bacteria; Streptococcus salivarius. Streptococcus'C', Staphylococcus albus and B. prodigiosus. Tests on E. coli with up to I to 2 p.p.m.v. in relatively dry air foed to destroy any organisms. This confwms ozone is a poor disinfectant at low humidities. However, at humidities above 60% tests confirmed pathogens can be destroyed by minute amounts of ozone.

Increasing the moisture content of the environment favorably influences germicidal effect. This is brought about by swelling of microbes making them more susceptible to destruction.

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