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Cutting boards in Salmonella cross-contamination
Cutting boards are commonly perceived as important fomites in cross-contamination of foods with agents such as Salmonella spp., despite the lack of supporting epidemiological data. A variety of woods and plastics have been used to make work surfaces for cutting. In general, wood is said to dull knives less than plastic, and plastic is seen as less porous than wood. Research to model the hypothetical cross-contamination has been done in a variety of ways and has yielded a variety of results. At least some of the work with knife-scarred plastic indicates that the surface is very difficult to clean and disinfect, although this may vary among the polymers used. High-density polyethylene, which is most used in commercial applications, has been shown to delaminate in response to knife scarring. Wood is intrinsically porous, which allows food juices and bacteria to enter the body of the wood unless a highly hydrophobic residue covers the surface. The moisture is drawn in by capillary action until there is no more free fluid on the surface, at which point immigration ceases. Bacteria in the wood pores are not killed instantly, but neither do they return to the surface. Destructive sampling reveals infectious bacteria for hours, but resurrection of these bacteria via knife edges has not been demonstrated. Small plastic cutting boards can be cleaned in a dishwasher (as can some specially treated wooden boards), but the dishwasher may distribute the bacteria onto other food-contact surfaces. Most small wooden boards (i.e., those with no metal joiners in them) can be sterilized in a microwave oven, but this should be unnecessary if accumulation of food residues is prevented. However, 2 epidemiological studies seem to show that cutting board cleaning habits have little influence on the incidence of sporadic salmonellosis. Further, one of these studies indicated that use of plastic cutting boards in home kitchens is hazardous, whereas use of wooden cutting boards is not.
Cutting Boards of Plastic and Wood Contaminated Experimentally with Bacteria
The microbiology of Plastic and wooden cutting boards was studied, regarding cross-contamination of foods in home kitchens. New and used Plastic (four polymers plus hard rubber) and wood (nine hardwoods) cutting boards were cut into 5-cm squares (blocks). Escherichia coli (two nonpathogenic strains plus type O157:H7), Listeria innocua , L. monocytogenes , or Salmonella typhimurium was applied to the 25-cm2block surface in nutrient broth or chicken juice and recovered by soaking the surface in nutrient broth or pressing the block onto nutrient agar, within 3-10 min or up to ca. 12 h later. Bacteria inoculated onto Plastic blocks were readily recovered for minutes to hours and would multiply if held overnight. Recoveries from wooden blocks were generally less than those from plastic blocks, regardless of new or used status; differences increased with holding time. Clean wood blocks usually absorbed the inoculum completely within 3-10 min. If these fluids contained 103-104CFU of bacteria likely to come from raw meat or poultry, the bacteria generally could not be recovered after entering the wood. If 106CFU were applied, bacteria might be recovered from wood after 12 h at room temperature and high humidity, but numbers were reduced by at least 98%, and often more than 99.9%. Mineral oil treatment of the wood surface had little effect on the microbiological findings. These results do not support the often-heard assertion that Plastic cutting boards are more sanitary than wood.
