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Bacteria on Cutting Boards

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Scott Martin & Susan Brewer

The incidence of foodborne illness in the United States each year has been estimated to be between 24 and 81 million cases (Archer and Kvenberg, 1985). Foodborne illness results in up to 9,000 deaths annually (Bennett et al., 1987) and costs up to $8.4 billion/year (Todd, 1989). Foodborne illness originates in foodservice establishments, in the home, in the food processing industry and from unknown breakdowns (60%); of those with identified sources, 79% originated in commercial facilities and 21% originated at home (IFT, 1995). While consumers are very concerned about "food safety" in general terms, they are much less concerned about microbiological hazards (Brewer et al., 1994). In addition, they generally have inadequate knowledge about measures to prevent foodborne illnesses in the home; only 54% of consumers said they would wash a cutting board with soap and water after chopping fresh meat and before cutting fresh vegetables for a salad (Williamson et al., 1992).

Cutting boards used to prepare raw meat can be used to prepare salad or other uncooked food, transferring disease- causing bacteria and other agents from the meat to the salad. Wooden cutting boards have been widely used for centuries, while boards made from various polymers have been available since the early 1970s. Glass cutting boards are a third option to consumers. Research has shown that when bacteria were inoculated on both wooden and polymer boards, bacterial recoveries from wooden boards generally were less than those from plastic boards, regardless of new or used status (Ak et al., 1994a). These authors found no differences between wood types (basswood, birch, maple, maple plus walnut). Cleaning with hot water and detergents was found to be effective in removing bacteria, regardless of the species, wood type, or whether the wood was new or used (Ak et al., 1994b). Little or no research has been performed using glass cutting boards. The objective of this study is to compare the potential of glass, wooden and plastic cutting boards to promote bacterial cross-contamination.

The Problematic Bacteria

Escherichia coli resides in the lower part of the intestinal tract and is the most common oxygen-tolerant microorganism (108-109/g) in the human large bowel. It is generally motile, able to grow on chemically defined medium and has more than 160 O antigens, 50 H antigens and 90 K antigens. Optimum growth temperature is 37°C; minimum is approximately 4°C and maximum is approximately 50°C. Optimum growth pH is 7.0; minimum pH for growth is 4.4, and maximum pH is 9.0. Minimum aw for growth is 0.96. Escherichia coli causes a number of extraintestinal diseases: wound infections, urinary tract infections and Gram negative septicemia. Diarrheagenic E. coli (DEC) is any strain of E. coli that has the potential to cause a diarrheal illness; four classes of DEC, based on distinct clinical symptoms, differences in epidemiology, and distinct O:H serogroups exist. These are: classical enteropathogenic E. coli (EPEC); enterotoxigenic E. coli (ETEC--these strains produce a heat-stable enterotoxin only, a heat-labile enterotoxin only, or both); enteroinvasive E. coli (EIEC; illness is the result of an invasive infection of the gastrointestinal tract); and enterohemorrhagic E. coli (EHEC; an "emerging pathogen"; caused by E. coli serotype O157:H7). Enterohemorrhagic E. coli was first characterized in the United States in 1982 following two outbreaks of human gastrointestinal illness. A toxin formed in the intestine causes acute hemorrhagic colitis. The organism is reported to survive refrigeration, and can multiply slowly at 6°C. The infectious dose is estimated to be between 10 and 100 cells. Symptoms include hemorrhagic colitis (bloody diarrhea) and severe abdominal cramps (100%), nausea, vomiting, and rarely fever; onset is three to six days (average four days) with duration lasting four to ten days (average four days). Complications include hemolytic uremic syndrome (HUS), a urinary tract infection.

Indicator organisms are used to determine fecal contamination because detection of pathogens is more difficult, less efficient, and more expensive. There are four characteristics of an indicator organism: (1) they grow only in the intestinal tract, (2) they are present in high numbers (at high dilutions they can be detected), (3) they are resistant to environmental stresses, and (4) they are easily and reliably detected.

Coliforms are defined as all aerobic and facultatively anaerobic, Gram negative, asporogenous rods able to ferment lactose with the production of acid and gas. These include species whose habitat is intestinal or nonintestinal (soil, water) and may include: Escherichia coli, Aeromonas hydrophila, Enterobacter cloacae, Klebsiella pneumoniae and Citrobacter species. Fecal coliforms are a division of coliforms that are considered to be of more recent fecal origin. They are distinguished by their ability to ferment lactose with the production of acid and gas at elevated temperatures between 43 to 45°C. Escherichia coli is a fecal coliform defined by biochemical characteristics. Because of the prevalence of E. coli in the human and animal intestine, and in their resultant stools, the presence of E. coli in processed foods is generally considered to indicate pollution of direct or indirect fecal origin.

Salmonella (common name salmonellae) are Gram-negative rods, which are usually mobile by means of peritrichous flagella. Many strains are capable of growth on a chemically defined medium, can use citrate as a carbon source, and are aerogenic (gas producing). Typical strains ferment neither lactose nor sucrose, and with few exceptions produce abundant H2S. Colonies produce characteristic reactions on differential media. The optimum temperature for growth of Salmonella is between 35 to 37°C. Slow growth has been observed at 5°C, with a maximum growth temperature between 45 to 47°C. Growth may occur between pH 4 (dependent upon the acid) and 9.0; optimum pH is between 6.5 to 7.5. Salmonella growth in liquid media has been observed between aw 0.999 and 0.945, although growth at an aw of 0.93 has been observed. A D value of 4 to 5 minutes at 60°C has been reported for Salmonella. Salmonella senftenberg 775W is one of the most heat-resistant strains known. A D value of 360 to 480 minutes at 70°C has been reported for this strain in milk chocolate. Salmonellae do not compete well with naturally occurring microorganisms normally found associated with food. Growth of Salmonella has been shown to be inhibited by food spoilage organisms, other members of the Enterobacteriaceae, and the lactic acid-producing bacteria.

The salmonellae are among the most ubiquitous microorganisms that cause bacterial diarrhea. The foodborne illness caused by Salmonella usually is expressed in one of two forms: gastroenteritis, the most common Salmonella disease, or enteric fever, such as typhoid or paratyphoid fever. Both of these illnesses are designated as foodborne infections, because viable cells are necessary to cause sickness.

The presence of Salmonella in food supplies presents an important health hazard to man. For this reason, federal regulations prohibit the presence of salmonellae in foods. The problem of detecting salmonellae in foods is made difficult as the result of two important factors: i) The microbial population of many foods is frequently very high (1010 organisms or greater per gram), while the number of Salmonella may be low; and ii) A variety of processing procedures may result in the presence of sublethally injured Salmonella, making them unable to grow readily. Additionally, there is inherent variability encountered in the analysis of various types of food. With these problems in mind, procedures have been developed for the qualitative determination for the presence of Salmonella.

Staphylococcus aureus are relatively fastidious bacteria, requiring the presence of amino acids and vitamins for aerobic growth, and uracil and a fermentable carbon source, for anaerobic growth. The optimum temperature for growth is 35°C, although growth occurs above the 10 to 45°C range. The pH range for growth is between 4.5 and 9.3; optimum is between pH 7.0 and 7.5. As environmental conditions become more restrictive, so does the pH range for growth. In general, S. aureus growth is repressed in the presence of competing microorganisms. Although D values differ with strain and heating menstruum, a D value of <3 minutes at 60°C indicates that S. aureus are not considered particularly heat-resistant. Staphylococcus aureus are resistant to temperatures below freezing but are sensitive to acidic environments and a variety of chemical compounds and antibiotics.

Staphylococcus aureus constitutes a normal part of the microflora of the animal body, which is found on skin surfaces and hair, and in the nose, mouth and throat. They are the most common cause of suppurative infections (boils and pimples), and are among the longest recognized of the pathogenic bacteria. Staphylococcus aureus is the causative agent of diseases such as pneumonia, endocarditis and scalded skin syndrome.

Staphylococcus aureus is a bacterial species of great concern to the food industry. Staphylococcal food poisoning is a leading cause of food-borne disease not only in the United States, but in many other countries as well. It consistently competes with salmonellosis as the most prevalent cause of food- related illness. It has been suggested that staphylococcal food poisoning is the leading cause of foodborne illness in the world. Staphylococcal food poisoning occurs as the result of the ingestion of a heat-stable, preformed enterotoxin, produced by the organism during growth.

References

Ak, N. O., D. O. Cliver and C. W. Kaspar. 1994a. Cutting boards
of plastic and wood contaminated experimentally with
bacteria. J. Food Protect. 57:16-22.

Ak, N. O., D. O. Cliver and C. W. Kaspar. 1994b.
Decontamination of plastic and wood cutting boards for
kitchen use. J. Food Protect. 57:23-30.

Archer, D.L. and Kvenberg, J.E. 1985. Incidence and cost of
foodborne diarrheal disease in the United States. J. Food
Protect. 48:887-894.

Bennett, J.V., Holmberg, S.D., Rogers, M.F., and Solomon, S.L.
1978. Infectious and parasitic diseases. In "Closing the Gap: The
Burden of Unnecessary Illness," Oxford University Press, New York.

Brewer, M.S., Sprouls, G.K. and Russon, C. 1994. Consumer
attitudes toward food safety issues. J. Food Safety 14:63-74.

IFT. 1995. Foodborne illness: Role of home food handling
practices. Food Technol. 49(4):120-131.

Todd, E.C.D. 1989. Preliminary estimates of the cost of foodborne
disease in the United States. J. Food Protect. 52:595-601.

Williamson, D.M., Gravani, R.B., and Lawless, H.T. 1992.
Correlating food safety knowledge with home food-preparation
practices. Food Technol. 46(5):94-100.

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  1. This document was produced by the Illinois Cooperative Extension Service, University of Illinois at Urbana-Champaign, School of Human Resources and Family Studies.

  2. Scott E. Martin, Ph.D., Professor, Department of Microbiology, and M. Susan Brewer, Ph.D., Associate Professor, Department of Food Science and Human Nutrition, University of Illinois, Urbana-Champaign, Illinois.

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