Methods for the removal of fecal contamination from beef carcass surfaces were evaluated using a fecal suspension containing a rifampicin-resistant strain of either Escherichia coli O157:H7 or Salmonella typhimurium. Paired cuts from four distinct beef carcass regions (inside round, outside round, brisket, and clod) were removed from hot carcasses after splitting, and subcutaneous fat and lean carcass surfaces from these cuts were used to model decontamination of prechilled carcass surface regions. Hot carcass surface regions were contaminated with an inoculated fecal suspension in a 400-cm2 area and then treated by one of four treatments either immediately or 20 to 30 min after contamination. One paired contaminated surface region from each carcass side was trimmed of all visible fecal contamination. The remaining paired carcass surface region was washed either with water (35°C) or with water followed by a 2% lactic or acetic acid spray (55°C). Surface samples were obtained for microbiological examination before and after treatment from within and outside the defined area contaminated with the fecal suspension. All treatments significantly reduced levels of pathogens; however, decontamination was significantly affected by carcass surface region. The inside round region was the most difficult carcass surface to decontaminate, regardless of treatment. Washing followed by organic acid treatment performed better than trimming or washing alone on all carcass region surfaces except the inside round, where organic acid treatments and trimming performed equally well. Overall, lactic acid reduced levels of E. coli O157:H7 significantly better than acetic acid; however, differences between the abilities of the acids to reduce Salmonella were less pronounced. All treatments caused minimal spread of pathogens outside the initial area of fecal contamination, and recovery after spreading was reduced by organic acid treatments.

The inhibition of Listeria monocytogenes by sodium lactate and sodium diacetate was evaluated for wieners containing pork, turkey, and beef and for cooked bratwurst containing beef and pork. Both products were supplied by commercial manufacturers. Treated products were surface-inoculated with 10(5) CFU of L. monocytogenes per package and vacuum-packed in gas-impermeable pouches. Wieners were stored for 60 days at 4.5 degrees C, and bratwurst were stored for 84 days at 3 and 7degrees C. A surface treatment that consisted of dipping wieners into solutions containing < or = 6% lactate and < or = 3% diacetate for 5 s did not delay pathogen growth compared with that for untreated wieners. In additional trials, the antilisterial activity of lactate and diacetate in wiener and bratwurst formulations was evaluated. Lactate levels ranged from 1.32 to 3.4%, and diacetate was evaluated at 0.1 and 0.25%. The growth of L. monocytogenes was delayed for 4 and 12 weeks at 7 and 3 degrees C, respectively, on uncured, unsmoked bratwurst formulated with 3.4% lactate/0.1% diacetate, compared with 1 and 2 weeks, respectively, for the formulation containing 2% lactate. L. monocytogenes grew by > or = 1 log unit after 4 weeks' storage at 3 or 7 degrees C on cured, smoked bratwurst without lactate or diacetate, but growth was inhibited for 12 weeks on cured, smoked bratwurst formulated with 3.4% lactate and 0.1% diacetate. Sodium lactate levels of > or = 3% and combinations of > or = 1% lactate plus > or = 0.1% diacetate prevented listerial growth on wieners stored for 60 days at 4.5 degrees C. These results indicate that dipping wieners in lactate-diacetate solutions is not an efficient way to apply these antimicrobial agents to wieners. However, the inclusion of combinations of sodium lactate and sodium diacetate in wiener or bratwurst formulations inhibits the growth of L monocytogenes at < or = 7 degrees C, and an additional margin of safety was observed for products that are cured and smoked.

Combining food antimicrobials can enhance inhibition of Listeria monocytogenes in ready-to-eat (RTE) meats. A broth dilution assay was used to compare the inhibition of L. monocytogenes resulting from exposure to nisin, acidic calcium sulfate, ε-poly-L-lysine, and lauric arginate ester applied singly and in combination. Minimum inhibitory concentrations (MICs) were the lowest concentrations of single antimicrobials producing inhibition following 24 h incubation at 35 °C. Minimum bactericidal concentrations (MBCs) were the lowest concentrations that decreased populations by ≥3.0 log(10) CFU/mL. Combinations of nisin with acidic calcium sulfate, nisin with lauric arginate ester, and ɛ-poly-L-lysine with acidic calcium sulfate were prepared using a checkerboard assay to determine optimal inhibitory combinations (OICs). Fractional inhibitory concentrations (FICs) were calculated from OICs and were used to create FIC indices (FIC(I)s) and isobolograms to classify combinations as synergistic (FIC(I) < 1.00), additive/indifferent (FIC(I)= 1.00), or antagonistic (FIC(I) > 1.00). MIC values for nisin ranged from 3.13 to 6.25 μg/g with MBC values at 6.25 μg/g for all strains except for Natl. Animal Disease Center (NADC) 2045. MIC values for ε-poly-L-lysine ranged from 6.25 to 12.50 μg/g with MBCs from 12.50 to 25.00 μg/g. Lauric arginate ester at 12.50 μg/g was the MIC and MBC for all strains; 12.50 mL/L was the MIC and MBC for acidic calcium sulfate. Combining nisin with acidic calcium sulfate synergistically inhibited L. monocytogenes; nisin with lauric arginate ester produced additive-type inhibition, while ε-poly-L-lysine with acidic calcium sulfate produced antagonistic-type inhibition. Applying nisin along with acidic calcium sulfate should be further investigated for efficacy on RTE meat surfaces.

Stationary-phase cultures of Escherichia coli O157:H7 were inoculated into tryptic soy broth, sealed in vials, and stored at -18 degrees C for 1, 8, and 15 days, or 3 or 15 degrees C for 3, 6, and 9 h. Thermal resistance was determined at 55 degrees C. Each storage treatment was repeated with additional holding at 23 or 30 degrees C for 1, 2, 3, or 4 h prior to heating to simulate potential temperature abuse during handling. Cultures under treatments enabling the growth of E. coli O157:H7 were generally more heat sensitive than those held at temperatures which restricted growth or enabled growth to stationary phase. Cultures stored frozen (-18 degrees C) without holding at elevated temperatures had greater heat resistance than those stored under refrigeration (3 degrees C) or at 15 degrees C. Subsequent holding of frozen cultures at 23 or 30 degrees C resulted in a decrease in heat resistance. To determine whether these responses would be observed under typical commercial preparation procedures, ground beef patties were inoculated with E. coli O157:H7 and stored at 3 or 15 degrees C for 9 h or at -18 degrees C for 8 d and then held at 21 or 30 degrees C for 0 or 4 h. Patties were grilled to an internal temperature of 54.4 degrees C (130 degrees F), 62.8 degrees C (145 degrees F), or 68.3 degrees C (155 degrees F). Cultures were most resistant in frozen patties, while cultures in patties stored at 15 degrees C were the most heat sensitive. Holding patties at 21 or 30 degrees C prior to grilling resulted in increased sensitivity. Storage and holding temperatures similar to those encountered in food service may influence the ability of E. coli O157:H7 to survive heat treatments.

Abstract. The incidence and severity of disease associated with toxigenic Clostridium difficile have increased in hospitals in North America from the emergence of newer, more virulent strains. Toxigenic C. difficile has been isolated from food animals and retail meat with potential implications of transfer to human beings. The objective of the present study was to determine the prevalence of C. difficile in pork from sausage manufacturing plants and retail meat in Texas. Twenty-three C. difficile isolates were detected from 243 meat samples (9.5%) from 3 sausage-manufacturing plants and 5 retail meat outlets from 2004 to 2009. Twenty-two isolates were positive for toxins A, B, and binary toxin, and were characterized as toxinotype V, PFGE type-NAP7, or "NAP7-variant." Susceptibilities to 11 antimicrobial agents in the current study were similar to those reported previously for toxinotype V isolates, although the results suggested somewhat reduced resistance than reported for other meat, animal, or human clinical toxinotype V isolates.

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A national survey of the nitrate ( NO3(-)) and nitrite ( NO2(-)) concentrations in raw and highly consumed vegetables available at retail in the United States was conducted. A total of 194 samples of fresh broccoli, cabbage, celery, lettuce, and spinach categorized as conventional or organic by label were collected from 5 major cities in different geographic regions of the United States and analyzed to determine NO3(-) and NO2(-) concentrations. There were no differences in the mean NO2(-) values of conventional compared with organic vegetables taken from the 5 metropolitan areas. However, significant differences in mean pairwise comparisons between some conventional and organic vegetables for NO3(-) content were observed. The mean NO2(-) concentration of both conventional and organic vegetables ranged between 0.1 and 1.2 mg/kg of fresh weight (FW) with the exception of conventional spinach that contained 8.0 mg/kg FW. Mean NO3(-) contents of conventional broccoli, cabbage, celery, lettuce, and spinach were 394, 418, 1496, 851, and 2797 mg/kg FW, respectively, while their organic-labeled counterparts averaged 204, 552, 912, 844, and 1318 mg/kg FW. In most cases, organic vegetables were numerically lower in NO3(-) content than their conventional counterparts. Based on survey results, the finding that low NO3(-) levels were observed in some organic vegetables in different cities may warrant further study to determine if true differences exist, due to production practices, seasonal differences, and the magnitudes of those differences. Furthermore, the geographic differences in NO3(-) content of vegetables may flaw estimates of daily NO2(-) and NO3(-) exposure.

A survey of residual nitrite (NO(2)(-)) and nitrate (NO(3)(-)) in cured meats available at retail was conducted to verify concentrations in conventional (C) products and establish a baseline for organic/natural/uncured/indirectly cured (ONC) products. In this study, 470 cured meat products representing six major categories were taken from retail outlets in five major metropolitan cities across the United States. Random samples representing both C and ONC type products were analyzed for NO(2)(-) and NO(3)(-) content (ppm) using an ENO-20 high-performance liquid chromatography system equipped with a reverse phase column. Generally, there were no differences in NO(2)(-) concentrations between C and ONC meat categories, but a few ONC products surveyed in certain cities were lower in NO(3)(-) content. Pairwise comparisons between cities indicated that NO(2)(-) and NO(3)(-) contents of all C type products were not appreciably different, and the same was true for most ONC products. Numerical NO(2)(-) values were less variable than NO(3)(-) concentrations within each meat product category. NO(2)(-) concentrations were similar to those previously reported by Cassens ( Cassens , R. G. Residual nitrite in cured meat . Food Technol. 1997a , 51 , 53 - 55 ) in 1997. Residual NO(2)(-) and NO(3)(-) values in this study were numerically lower than those reported by NAS ( National Academy of Sciences . The Health Effects of Nitrate, Nitrite, and N-Nitroso Compounds ; National Academy Press : Washington, DC , 1981 ) in 1981. Data from this survey provide a benchmark of NO(2)(-) and NO(3)(-) concentrations for ONC products available at retail.