Chlorine dioxide helps reduce pathogen levels on cardboard surfaces.

Chlorine dioxide (Cl[O.sub.2]2) is an antimicrobial substance recognized for its disinfectant properties since the early 1900s. Chlorine dioxide kills microorganisms by disrupting the transport of nutrients across the cell wall. It can be generated in a gas or liquid form and smells like chlorine bleach. But chlorine dioxide should not be confused with chlorine gas. They are two distinct chemicals that react differently and produce by-products that also have little in common.

Since chlorine dioxide is used as an antimicrobial agent in sanitizers and disinfectants, researchers at Kansas State University wanted to examine its antimicrobial effectiveness at 500 ppm against foodborne pathogens found on cardboard surfaces. They found that chlorine dioxide might induce a 5 log cfu per [cm.sup.2] or higher reduction of bacterial contamination on cardboard surfaces.

Five strains of E. coli O157:H7 and Salmonella spp. were grown in brain hearth infusion broth at 37 C for 24 hours. The scientists mixed equal amounts of E. coli O157:H7 strains and Salmonella spp. to prepare the cultures. They inoculated the sterilized cardboard samples (7x7 [cm.sup.2]) with a cocktail of E. coli O157:H7 or Salmonella spp. The samples were kept at 8 C for 30 minutes so that bacterial attachment could occur.

Then the investigators sprayed an inoculation chamber with a 500-ppm chlorine dioxide solution for 15 minutes. The cardboard samples were placed in the center of the chamber and sprayed with the same solution for 30 minutes to establish a mist of 500-ppm chlorine dioxide.

The scientists kept the cardboard samples in the container for another 30 min. Then a 5x5 [cm.sup.2] piece was excised from the cardboard samples for microbiological analysis. The number of E. coli O157:H7 and Salmonella spp. was determined using MacConkey Sorbitol Agar and XLD Agar, respectively.

The scientists incubated the agar plates at 37 C for 24 hours. The initial inoculum level was 5.7 logs cfu per [cm.sup.2] for both pathogens. The number of E. coli O157:H7 strains and Salmonella spp. was reduced below detection levels after the 500-ppm chlorine dioxide treatment.

Further information. James Marsden, Department of Animal Sciences and Industry, Kansas State University, 226 Weber Hall, Manhattan, KS 66506; phone: [phone]; fax: [phone]; email: [e-mail].