The microbiological quality of ready-to-eat (RTE) foods from school cafeterias in Chongqing, China, was evaluated in comparison to a guideline published by a provincial health commission. Based on their preparation processes and potential risks, the RTE foods were divided into 5 types: food type 1, general cooked and hot-held foods; food type 2, cooked meats; food type 3, heated aquatic products; food type 4, fresh fruit/vegetables; and food type 5, cooked foods with post-cook processes (e.g. cut, cool, addition of ingredients/condiments, etc.). Food type 1-3 (subjected to thermal processes, and hot-held) were microbiologically safer than type 4 and 5 (prepared by non-thermal process or post-cook processes). None of the samples in food type 1-3 were unsatisfactory for aerobic plate counts (APC) and total coliforms (TC), whereas 43.1% of food type 4, 8.3% and 71.7% of type 5 samples were unsatisfactory due to high counts of TC, APC, and TC, respectively. Two, 12, and 50 samples from type 2, 4, and 5, respectively, were unacceptable due to high levels of Staphylococcus aureus . Bacillus cereus and Vibrio parahaemolyticus were detected but under the satisfactory limits. None of the samples tested positive for Salmonella , Listeria monocytogenes , and Escherichia coli O157. The collected data of the bacterial profile can be used by policymakers and epidemiologists in microbiological risk assessments, which may be conducive to develop interventions to control the hazards, improve food hygiene, and safety management systems for school cafeterias in China.
Studies were done at 21°C to determine the bactericidal activity of lactic acid, levulinic acid, and sodium dodecyl sulfate (SDS) applied individually and in combination on Shiga toxin–producing Escherichia coli (STEC) in pure culture and to compare the efficacy of lactic acid and levulinic acid plus SDS treatments applied by spray or immersion to inactivate STEC and Salmonella (10 7 CFU/cm 2 ) on beef trim pieces (10 by 10 by 7.5 cm). Application of 3% lactic acid for 2 min to pure cultures was shown to reduce E. coli O26:H11, O45:H2, O111:H8, O103:H2, O121:H2, O145:NM, and O157:H7 populations by 2.1, 0.4, 0.3, 1.4, 0.3, 2.1, and 1.7 log CFU/ml, respectively. Treatment with 0.5% levulinic acid plus 0.05% SDS for <1 min reduced the populations of all STEC strains to undetectable levels (>6 log/ml reduction). Beef surface temperature was found to affect the bactericidal activity of treatment with 3% levulinic acid plus 2% SDS (LV-SDS). Treating cold (4°C) beef trim with LV-SDS at 21, 62, or 81°C for 30 s reduced E. coli O157:H7 by 1.0, 1.1, or 1.4 log CFU/cm 2 , respectively, whereas treating beef trim at 8°C with LV-SDS at 12°C for 0.1, 1, 3, or 5 min reduced E. coli O157:H7 by 1.4, 2.4, 2.5, or 3.3 log CFU/cm 2 , respectively. Spray treatment of beef trim at 4°C with 5% lactic acid only reduced the E. coli O157:H7 population by 1.3 log CFU/cm 2 . Treating beef trim at 8°C with LV-SDS for 1, 2, or 3 min reduced Salmonella Typhimurium by 2.1, 2.6, and >5.0 log CFU/cm 2 , respectively. Hand massaging the treated beef trim substantially reduced contamination of both pathogens, with no detectable E. coli O157:H7 or Salmonella Typhimurium (<5 CFU/cm 2 ) on beef trim pieces treated with LV-SDS. Reduction of E. coli O157:H7 and Salmonella Typhimurium populations was enhanced, but bactericidal activity was affected by the meat temperature.
The ability of Listeria monocytogenes and two competitive exclusion (CE) bacteria, Lactococcus lactis subsp. lactis strain C-1-92 and Enterococcus durans strain 152, to form biofilms on coupons composed of different materials (stainless steel, plastic, rubber, glass, and silicone) was determined at 4 and 8°C. Biofilm characteristics were determined by scanning electron microscopy. L. monocytogenes produced well-formed biofilms within 24 h at 37°C on coupon surfaces. Treating Listeria -laden biofilms with the CE isolates individually at either 4 or 8°C for 3 weeks substantially reduced or eliminated listeriae in the biofilms. Treatment with L. lactis subsp. lactis strain C-1-92 and E. durans strain 152 at 4°C for 3 weeks reduced the population of L. monocytogenes in a biofilm from 7.1 to 7.7 log CFU/cm 2 to 3.0 to 4.5 log CFU/cm 2 and to 3.1 to 5.2 log CFU/cm 2 , respectively, and treatment at 8°C for 3 weeks reduced L. monocytogenes from 7.5 to 8.3 log CFU/cm 2 to 2.4 to 3.5 log CFU/cm 2 and to 3.8 to 5.2 log CFU/cm 2 , respectively, depending on the coupon composition. These two CE isolates were combined and evaluated for control of Listeria bacteria in floor drains of a ready-to-eat poultry processing plant. The results revealed that treating the floor drains with CE four times in the first week eliminated detectable Listeria bacteria from five of six drains, and the drains remained free of detectable Listeria bacteria for 13 weeks following the first four treatments. These studies indicate that CE can effectively reduce Listeria contamination in biofilms and in flow drains of a plant producing ready-to-eat poultry products.