Ozone Inactivation of Streptococcus Faecalis and Staphylococcus Aureus in Water as Models of Gram (-) Bacteria I. Lezcano, R. Pérez-Rey, E. Sánchez, Ch. Baluja, C. Alvarez. Ozone Research Center, Cuba. Ozone is a potent germicidal agent. Inactivation kinetics of Pseudomonas aeruginosa and Escherichia coli towards ozone in water, as models of Gram (-) bacteria, were studied. For this purpose, water suspensions of 104 - 106 CFU/ml of Pseudomonas aeruginosa and Escherichia coli isolated from polluted water and Pseudomonas aeruginosa ATCC 27853 and Escherichia coli ATCC 25922, were prepared in sterile conditions and treated in a 100 mL bubble reactor with ozone, achieving concentrations from 0.3 to 2.61 mg of dissolved ozone/L of water, in contact with microorganisms. Total inactivation obtained by this procedure varied from 1.04 to 19.23 minutes depending on the bacterial resistance and the ozone concentration applied. The ATCC strains showed to be more sensitive than the environmental isolates; Pseudomonas aeruginosa was the most resistant wild strain. First order inactivation kinetics respect to both the concentrations of ozone and microorganisms were found, resulting an overall second order inactivation kinetics. Source: 2nd International Symposium on Ozone Applications Havana, Cuba - Mach 24-26, 1997.