BIOFILM DEVELOPMENT AND SANITIZER INACTIVATION OF LISTERIA-MONOCYTOGENES AND SALMONELLA-TYPHIMURIUM ON STAINLESS-STEEL AND BUNA-N RUBBER

Biofilm formation by seven strains of Listeria monocytogenes and one strain of Salmonella typhimurium on stainless steel and Buna-n rubber was examined under two nutrient conditions. The type of surface, nutrient level, and organism influenced biofilm development and production of extracellular materials. Buna-n had a strong bacteriostatic effect on L monocytogenes, and biofilm formation on Buna-n under low nutrient conditions was reduced for four of the seven strains tested. Buna-n was less bacteriostatic toward S. typhimurium. It inhibited the growth of several other pathogens to varying degrees. An ethylene propylene diamine monomer rubber was less inhibitory than Buna-n, and Viton rubber had no effect. The effectiveness of sanitizers on biofilm bacteria was examined. Biofilms were challenged with four types of detergent and nondetergent sanitizers. Resistance to sanitizers was strongly influenced by the type of surface. Bacterial biofilm populations on stainless steel were reduced 3-5 log by all the sanitizers, but those on Buna-n were resistant to these sanitizers and were reduced less than 1-2 log. In contrast, planktonic (suspended) bacteria were reduced 7-8 log by these sanitizers. Chlorine and anionic acid sanitizers generally removed extracellular materials from biofilms better than iodine and quaternary ammonium detergent sanitizers. Scanning electron microscopy demonstrated that biofilm cells and extracellular matrices could remain on sanitized surfaces from which no viable cells were recovered.