Impact of Environmental Stressors on Susceptibility of Salmonella in Processing Plants

Non-Technical Summary:<br/>
When enteric pathogens are exposed to environmental stresses such as acidic or thermal conditions, some of the exposed cells develop either a tolerance or resistance to these stressors. Various studies have speculated that these stress adapted cells exhibit enhanced resistance to other environmental stressors including those from thermal processing and acid exposure. The magnitude of this increased resistance to other environmental stressors is such that some of the adapted cells could potentially survive the current minimum guidelines for cooking of meat and poultry or the minimum doses of antimicrobials used in processing for control of foodborne pathogens. Current industry practices present a wide scope for foodborne pathogens to be exposed to sub-lethal thermal treatments or antimicrobials which are widely used as microbial interventions during day-to-day meat and poultry processing operations. These treatments are a critical part of a processors food safety Hazard Analysis and Critical Control Point (HACCP) system to ensure safety of meat and poultry products. Preliminary laboratory data suggests that increased resistance as a result of sub-lethal heat exposure or acid exposure could potentially create an unexpected foodborne hazard leading to implications to public health. The limitations of the existing research are that it has been conducted in either laboratory media or in foods that are held in conditions which do not reflect the current practices of storage and distribution of processed meat and poultry. To confirm the laboratory observations and improve our knowledge of stressed bacteria studies need to be conducted in an actual food system for more accurate inferences and reducing the knowledge gaps.
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Approach:<br/>
Salmonella spp. will be grown in laboratory media (Brain Heart Infusion; BHI) supplemented with 1 percent glucose (BHI plus 1 percent Glucose) to a stationary phase and held for 12-18 hours. The inclusion of glucose allows for the production of organic acids, which lowers the final pH of the culture medium significantly without acid-shocking the bacterial cultures. Thermal tolerance of acid adapted cells will be determined by decimal reduction values (D-values) and compared to those of non-adapted cells. D-values will be determined in BHI and BHI plus 1 percent glucose broths.Heat tolerant cultures of Salmonella spp. will be developed by growing multiple strains in BHI medium maintained at sub-lethal temperatures for 18-24 hours in the stationary phase. The purpose of growing cultures in sub-lethal temperatures is to select for heat tolerant strains that can be tested for resistance to other stressors such as organic acids. Heat tolerant cells will then be enumerated by growing on laboratory media supplemented with glucose and compared to those grown in regular media. A comparison of this will illustrate level of cross protection obtained as a result of heat shock/ adaptation. Poultry carcasses will be inoculated with stress adapted (acid and heat) bacteria while non-adapted strains will be separately inoculated to serve as controls.Inoculated chicken carcasses will then be treated by spraying organic acids in varying concentrations and held at 4 C for up to 24 hours to allow maximum attachment of bacteria. As an additional set of controls, adapted and non-adapted bacteria will be inoculated onto the chicken carcasses, held at 4 C for up to 24 hours without treatment with organic acid rinses. The thermal tolerance of Salmonella spp. will be determined in laboratory media and in the inoculated ground meat (chicken) by comparing decimal reduction values (D-values) at different temperatures. Briefly, 5 g of inoculated ground chicken will be placed in a vacuum bag, pressed to obtain as thin a thickness as possible, and sealed. These bags will be immersed in water baths set at appropriate temperatures (52, 58, and 62 C) and the timing will start as soon as the set point is reached. Control bags with thermocouples will serve as temperature monitors. Similarly D-values of the bacteria will be measured in the inoculated laboratory media and the D-values will be compared to that of the bacteria inoculated into ground chicken. Because of the high probability of injured bacteria as a result of exposure to stressors such as heat and acid, the bacterial populations will be enumerated on selective and non-selective media (Buchanan and Edelson 1999 noted as much as a 5 log10 difference between injured and un-injured populations). Initial experiments will be conducted to determine optimal incubation conditions (for example 25 C for 72 h compared to 37 C for 48 h) for maximum recovery of the injured bacteria.
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Progress:<br/>
2012/01 TO 2012/12<br/>
OUTPUTS: Current food safety trends focus on achieving best practices in pathogen control. Many interventions strategies have been investigated to eliminate Campylobacter both ante-mortem and post-mortem. The bactericidal activity of intervention treatments relies heavily on the disruption of an organism's physiological processes and treatments in experimental research are validated based on the log10 scale. These intervention processes can be categorized as: thermal, irradiation-based, and chemical based. Application of approved chemical treatments during processing is another method to reduce pathogens on poultry carcasses. In order for antimicrobials to be effective and relevant to the industry, they must be approved and have validated efficacy against microorganisms. In addition, the concentration and contact time needs to be appropriate for a particular processing step. Finally, they must be cost effective and without negative impacts on product quality. Chemical antimicrobials are evaluated for many different factors and their use on meat, poultry, and other food products should be approved by the appropriate regulatory agencies. While worker safety and production of harmful effluents should be monitored and minimized for environmental concerns, another important concern is that a chemical antimicrobial should not have any organoleptic effects on the products. In commercial poultry chilling process, chemical intervention strategies used have evolved over time.
<br/>PARTICIPANTS: Nothing significant to report during this reporting period. <br/>TARGET AUDIENCES: Nothing significant to report during this reporting period. <br/>PROJECT MODIFICATIONS: Nothing significant to report during this reporting period.
<P>Impact: We have been able to perform surveys and tabulate practices that are being followed in the poultry processing plants and better understand high risk areas within a plant and the interventions being used against foodborne pathogens. By understanding high risk areas and testing for pathogens throughout the plants, suggestions are being developed for implementation in plants in order to reduce the risk of contamination of poultry.