Comparison of efficacy of ozone and chlorine as antimicrobial agents against planktonic cells and biofilms of Shewanella putrefaciens
Creators: name: Nunez San Martin, Angela
Publisher: name: University of British Columbia
Year: 2009

description: The purpose of this study was to compare the efficacy of ozone and chlorine as antimicrobial agents against planktonic cells and biofilms of Shewanella putrefaciens. Shewanella putrefaciens is an intensive psychrotrophic spoilage organism of proteinaceous foods; in particular, fish. Because of the importance of this organism in the spoilage of seafood and the present use of ozone in some fishing boats, the antimicrobial tests were performed in cold environments characteristic of seafood processing plants and fish boats. For each planktonic and biofilm set of tests, there were 6 treatments to reflect a 3 x 2 factorial experiment. The factors were sanitizer type and temperature. The sanitizing agents employed were: no sanitizer (control), ozone and chlorine. The two experimental temperatures were 10° ± 0.5°C and 0.5° ± 0.5°C. Results of this study confirmed literature data that both chlorine and ozone are good biocidal agents. However, planktonic tests showed that ozonated distilled-deionized water at 0.25 ppm was more than 70 times more effective in inactivating Shewanella putrefaciens than distilled-deionized water containing 1.0 ppm available chlorine. Most of the microbial inactivation by either chlorine or ozone took place within the initial 30 sec. This inactivation was accompanied by a corresponding decrease in chlorine and ozone levels. After the initial decline, the surviving planktonic population remained stable. On the other hand, microbial inactivation data indicated that distilled-deionized water containing 1.0 ppm available chlorine was more effective than 0.25 ppm ozonated distilled-deionized water in inactivating Shewanella putrefaciens biofilms grown on stainless steel chips. Biofilm populations exposed to either ozone or chlorine showed an initial sharp decline in their numbers within the initial 30 sec of exposure. After this period, the biofilm populations exposed to ozonated water declined at a slower rate. Biofilm populations exposed to 1.0 ppm available chloripe had a faster rate of cell inactivation as indicated by their steeper inactivation curves and final biofilm population. The tests also revealed that the indigo trisulfonate method may not be suitable to measure ozone concentrations in suspensions containing large number of organisms. Bacterial cells were shown to adsorb the indigo trisulfonate dye used to measure ozone concentration and thus cause incorrect determination of ozone concentrations. No mention of this problem had been found in searches of scientific literature. Thus, to overcome this major obstacle, the procedure used to determined ozone concentration had to be modified. In short, the interference caused by the bacteria and adsorbed indigo trisulfonate dye had to be removed prior to any determination of ozone concentration. This modified procedure to measure ozone concentration in microbial suspension was practical but it was also far from ideal. A new method must be derived Jhat has all the advantages of the indigo trisulfonate method but that does not interact with the microorganisms. This is very important given the reactive nature of ozone as well as its potential as a sanitizer not only in the food processing area but in fields such as aquaculture, wastewater and potable water treatments.