A biofilm is defined as a “microbially-derived sessile community which is characterized cells that are irreversibly attached to a substratum or interface, or to each other” are embedded in a matrix of extracellular polymeric substances (EPS). More simply put, microorganisms attach to surfaces and develop biofilms. Biofilms can be found in natural environments, on surfaces around the home, but more alarmingly, they can be found in food processing facilities.
Cells in a biofilm have the ability to survive cleaning and sanitization. The resistance to sanitizers increases with the maturity of the biofilm. In the last decade, a number of studies have been conducted to determine a variety of sanitizers’ efficacy against biofilms. In 2010, the Department of Food Science at Purdue University compared the effect of chlorine dioxide gas, aqueous chlorine dioxide, and aqueous sodium hypochlorite treatments on the inactivation of listeria monocytogenes containing biofilms. Listeria monocytogenes is a food-borne pathogen with the highest mortality rate. It has the ability to adhere to and grow on a variety of surfaces found in food processing plants. The study proved that the biofilm developed from the five-strain mixture was more resistant to the sodium hypochlorite treatment than either chlorine dioxide (CD) option. Aqueous CD resulted in significantly greater log reduction of biofilm cells for shorter treatment times as compared to CD gas treatment. However, once the CD gas dissolved in the water present, it was similar in effectiveness.
This comparison of chlorine dioxide’s efficacy against biofilms in both the gaseous or aqueous state was taken a step further by the Republic of Korea’s Department of Biotechnology and University of Georgia’s Center for Food Safety in 2014. This team evaluated chlorine dioxide’s ability to kill Bacillus cereus spores in biofilm formed on a stainless steel surface. Bacillus cereus is a spore-forming bacterium that can cause foodborne diseases. The study pointed out that while aqueous CD has “the advantage of being easy to produce and handle compared to gaseous ClO2,” its residual moisture may promote the growth of molds after treatment of food-contact surfaces. It was determined that the antimicrobial activity of chlorine dioxide gas was higher than that of the aqueous, and spores were inactivated within one hour.
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