Food Protection Trends - November 2008 - 761

(12, 17). There are 16 serovars but not all of them appear to be pathogenic. Most diseases are caused by serotypes 4b, 1/2a, and 1/2b, with 90% of these isolates found in processing areas (11). Because of its ubiquitous nature, L. monocytogenes is a difficult organism to control, especially in areas where ready-to-cook items are processed. L. monocytogenes can be inactivated in meat products heated to 70°C. However, because L. monocytogenes typically enters the food supply from the processing plant environment through cross contamination or environmental contamination after a heat treatment has been applied, it has become a major concern for the meat processing industry (16, 31). The attachment of bacteria and subsequent development of biofilms are a concern in food processing environments. Biofilms, which can lead to product contamination and spoilage (34, 35), can be characterized as complex bacterial communities in which the number of organisms, the type of bacterial species, and their interactions depend upon where the biofilm develop (23). Biofilms can form in a hydrated environment with the proper nutrients on a variety of hydrophobic and hydrophilic surfaces, including glass, metals, and plastics (26, 27). Biofilms in ready-toeat (RTE) meats have received increased interest recently because of potential cross contamination by L. monocytogenes embedded in the biofilms. This pathogen is of particular interest because it is commonly found in diverse environments, including soil, water, animal feed and animal feces (33); it can be isolated from refrigerated conditions; and it is a frequent resident in food processing plants (20). A particular challenge in minimizing microbial accumulations on equipment surfaces is the ability of many bacteria to produce extracellular polysaccharides that anchor cells to product contact and non-contact surfaces, creating biofilms. Biofilms can be defined as matrix-enclosed bacterial populations adhering to a surface or to each other. Biofilms in nature can have various levels of organization, as they exist in single or multiple species communities, which may form single or three-dimensional structures, or they may form aggregates such as flocs and granules (1, 5, 9). A natural biofilm community may function through collective behavior and coordinated activity, which assists survival of constituent cells in stressful environments. The majority of microorganisms in natural habitats are attached to surfaces (14), indicating the extent of the selective advantage for biofilm growth. Poor sanitation and hygienic conditions of food contact surfaces, equipment, and plant processing environments can contribute to foodborne disease outbreaks caused by pathogens such as L. monocytogenes and Salmonella. Improperly cleaned surfaces, plus the presence of water, contribute to the development of bacterial biofilms that may contain pathogenic microorganisms (6). The danger associated with biofilm formation is that over time, the sheltered and anchored bacteria can become loosened and can contaminate product flowing over the biofilms. This action can result in product contamination over time and a potential for recalls. Another danger is that bacteria in biofilms are more resistant to heat and in general are more resistant to removal by cleaning agents and destruction by sanitizers (18, 24, 26, 29, 32). Biofilms generally form in crevices and hard-to-reach places. Therefore, hygienically designed conveyor belts can minimize the risk associated with biofilms and can help reduce biofilm formation. An especially important and often overlooked consideration in manufacture of sanitary equipment is the design of conveyor belts. The high usage and hard-to-clean areas of conveyor belts make them excellent environments for bacterial harborage and biofilm formation. Recently, an equipment manufacturer began to modify its belts by forming a one-piece integrated shaft / drive component assembly. Having the drive shafts and components machined from a single piece of metal improves cleanability, decreases water pooling that can harbor bacteria, and helps to eliminate the possibility of pathogens harboring between a shaft and gear or in other hard-to-clean areas of the drive system. Another important design detail improving sanitation lies in the ease of disassembly and reassembly of equipment and conveyor belts. Equipment designs that facilitate rapid, easy disassembly without tools can promote proper cleaning and maintenance of equipment. For example, open mesh belts with 70% open structure do not need to be removed from the conveyor system for cleaning. Not only do these open mesh belts make the practice of removing belts prior to cleaning easy, but their open structures maximize product exposure, making these belts exceptionally suitable for drainage, convection air current and batter coating applications. Also, designs such as these open belt structures reduce or eliminate areas where product or debris can become lodged and improve product safety by decreasing the potential for biofilm formation. In previous studies, a variety of experimental procedures were used to determine biofilm attachment, making it difficult to draw practical conclusions for application by processors. Many studies included biofilms that were developed between 8 to 14 days before being evaluated, although the clean-up period in the processing plant usually does not allow more than 18–48 hours for biofilm buildup (8, 13). Generally, the clean-up and sanitation periods (or third shift) occur after two full production shifts totaling 16–18 h. Therefore, if clean-up and sanitation are performed properly, there should be only a 16–18 h time frame from clean-up to clean-up for biofilms to form. However, weekends can extend this time frame by adding an additional 24–28 hours between clean ups. In this research, our objective was to determine the impact of various materials encountered in processing plant environments on the attachment of, and biofilm formation by, L. monocytogenes. In this project we standardized some of the variables reported in previous biofilm studies with L. monocytogenes. It can be assumed that bacterial attachment to all food surfaces does occur, and understanding the phenomenon of the design of processing belts would be advantageous to meat and poultry industries with respect to product qual- NOVEMBER 2008 | FOOD PROTECTION TRENDS 761

Food Protection Trends - November 2008

Table of Contents for the Digital Edition of Food Protection Trends - November 2008