Prevalence and control of Listeria, Salmonella and Escherichia coli O157:H7 in Colorado rural households
Date
2009
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Abstract
The household environment has been linked to multiple outbreaks of foodborne illnesses, including listeriosis and salmonellosis. The food handling habits of consumers play a critical role in the food chain continuum, and need to be investigated to better prevent foodborne illnesses that originate at home. The objective of this work was to identify risk factors associated with prevalence of Listeria, Salmonella and Escherichia coli 0157:H7 in the rural household environment, and to provide scientific data for the development of reheating instructions for frankfurters in the home setting. To study risk factors associated with Listeria, Salmonella and Escherichia coli 0157:H7 prevalence in rural Colorado households with or without ruminants, households were recruited, and samples from food and the environment, as well as behavioral data from the primary foods preparer in the house, were collected. Listeria was isolated from refrigerators, kitchen sinks, shoes soles, clothes washing machine and food samples, with higher prevalence in households with ruminants. No sample was found positive for E. coli 0157:H7, and Salmonella was isolated from one refrigerator, one washing machine, one working glove, and two shoe samples. Results indicated that behavior related to handling and cooking of perishable foods affected the probability of household samples testing positive tor Listeria, regardless of presence of ruminants. Personal cleanliness habits were related to presence of Listeria on shoe soles, clothes washing machine, and working gloves. Shoes testing positive in households with ruminants were more frequently associated with multiple positive environmental samples compared to households without ruminants. Results indicated that consumer education on handling and storing perishable foods, and animal handling to prevent contamination of the household through shoes or clothes may reduce prevalence of Listeria in home environments. Two studies evaluated reheating of frankfurters inoculated with L. monocytogenes with or without antimicrobials. In both cases, frankfurters were formulated with or without 1.5% potassium lactate and 0.1% sodium diacetate and were inoculated with a ten-strain composite of L. monocytogenes. After inoculation, frankfurters were vacuum packaged and stored under conditions simulating manufacturing/retail and consumer storage. In one study, after the appropriate storage time, frankfurters were placed in a bowl with water and treated in a household microwave oven. Exposure to high power for 75 s reduced pathogen levels (0.7±0.0 to 1.0±0.1 log CFU/cm2) to below the detection limit (<-0.4 log CFU/cm2) on frankfurters with actate/diacetate. On frankfurters without lactate/diacetate, initial levels of L. monocytogenes (1.5±0.1 to 7.2±0.5 log CFU/cm2) on untreated samples increased as storage in vacuum and aerobic packages progressed. For this formulation, the exposure to high power for 75 s produced reductions between >1.5 and 5.9 log CFU/cm2. Depending on the treatment and storage time, the water used to reheat the frankfurters had viable L. monocytogenes counts of <-2.4 to 5.5±0.5 log CFU/ml. Results indicated that levels of L. monocytogenes contamination <3.7 log CFU/cm2, on frankfurters can be significantly (P>0.05) reduced by microwave oven heating at high power for at least 75 s. Higher contamination levels, such as those found on frankfurters without lactate/diacetate and stored for a prolonged period of time, require longer exposure to microwave heating in order to render the product safe for consumption. In the other study, inoculated frankfurters were treated with hot water after different storage periods to evaluate the destructiveness of different time and water-temperature combinations L. monocytogenes. Treatments at 80°C (60, 120 s) and 94°C (30, 60 s) reduced pathogen counts on frankfurters with PL/SD to at/below the detection limit (<-0.4 log CFU/cm) from initial levels on control (immersed in 25°C water for 300 s) samples. For frankfurters without PL/SD, where pathogen numbers reached 6.1 log CFU/cm2 on 60-day old vacuum-packaged product stored aerobically for 7 days, hot water treatments reduced counts by 1.0 (30 s/80°C) to >6.0 (120 s/94°C and 300 s/94°C) log CFU/cmz. No survivors were detected in the heated water after any treatment (detection limit <-2.5 log CFU/ml). While low levels of L. monocytogenes on frankfurters can be inactivated with short exposure to hot water, increased contamination that may occur as the product ages needs longer times and/or higher temperature for inactivation.
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Subject
Escherichia coli O157:H7
Listeria
reheating
rural households
Salmonella
microbiology
food science