Xiangwu Nou

Seasonal Prevalence of Shiga Toxin–Producing Escherichia coli, Including O157:H7 and Non-O157 Serotypes, and Salmonella in Commercial Beef Processing Plants†

The seasonal prevalence of Escherichia coli O157:H7, Salmonella, non-O157 E. coli (STEC), and stx-harboring cells was monitored at three Midwestern fed-beef processing plants. Overall, E. coli O157:H7 was recovered from 5.9% of fecal samples, 60.6% of hide samples, and 26.7% of carcasses sampled before the preevisceration wash. This pathogen also was recovered from 1.2% (15 of 1,232) of carcasses sampled at chilling (postintervention) at approximate levels of <3.0 cells per 100 cm2. In one case, the E. coli O157:H7 concentration dropped from ca. 1,100 cells per 320 cm2 at the preevisceration stage to a level that was undetectable on ca. 2,500 cm2 at the postintervention stage. The prevalence of E. coli O157:H7 in feces peaked in the summer, whereas its prevalence on hide was high from the spring through the fall. Overall, Salmonella was recovered from 4.4, 71.0, and 12.7% of fecal, hide, and preevisceration carcass samples, respectively. Salmonella was recovered from one postintervention carcass (of 1,016 sampled). Salmonella prevalence peaked in feces in the summer and was highest on hide and preevisceration carcasses in the summer and the fall. Non-O157 STEC prevalence also appeared to vary by season, but the efficiency in the recovery of isolates from stx-positive samples ranged from 37.5 to 83.8% and could have influenced these results. Cells harboring stx genes were detected by PCR in 34.3, 92.0, 96.6, and 16.2% of fecal, hide, preevisceration carcass, and postintervention carcass samples, respectively. The approximate level of non-O157 STEC and stx-harboring cells on postintervention carcasses was > or = 3.0 cells per 100 cm2 for only 8 of 199 carcasses (4.0%). Overall, the prevalence of E. coli O157:H7, Salmonella, and non-O157 STEC varied by season, was higher on hides than in feces, and decreased dramatically, along with pathogen levels, during processing and during the application of antimicrobial interventions. These results demonstrate the effectiveness of the current interventions used by the industry and highlight the significance of hides as a major source of pathogens on beef carcasses.

Effect of chemical dehairing on the prevalence of Escherichia coli O157:H7 and the levels of aerobic bacteria and enterobacteriaceae on carcasses in a commercial beef processing plant.

The objective of this experiment was to test the hypothesis that cleaning cattle hides by removing hair and extraneous matter before hide removal would result in improved microbiological quality of carcasses in commercial beef processing plants. To test this hypothesis, we examined the effect of chemical dehairing of cattle hides on the prevalence of Escherichia coli O157:H7 and the levels of aerobic bacteria and Enterobacteriaceae on carcasses. Samples from 240 control (conventionally processed) and 240 treated (chemically dehaired before hide removal) hides (immediately after stunning but before treatment) and preevisceration carcasses (immediately after hide removal) were obtained from four visits to a commercial beef processing plant. Total aerobic plate counts (APC) and Enterobacteriaceae counts (EBC) were not (P > 0.05) different between cattle designated for chemical dehairing (8.1 and 5.9 log CFU/100 cm2 for APC and EBC, respectively) and cattle designated for conventional processing (8.0 and 5.7 log CFU/100 cm2 for APC and EBC, respectively). However, E. coli O157:H7 hide prevalence was higher (P < 0.05) for the control group than for the treated group (67% versus 88%). In contrast to hides, the bacterial levels were lower (P < 0.05) on the treated (3.5 and 1.4 log CFU/100 cm2 for APC and EBC) than the control (5.5 and 3.2 log CFU/100 cm2 for APC and EBC) preevisceration carcasses. Prevalence of E. coli O157:H7 was lower (P > 0.05) on treated than on control preevisceration carcasses (1% versus 50%). These data indicate that chemical dehairing of cattle hides is an effective intervention to reduce the incidence of hide-to-carcass contamination with pathogens. The data also imply that any effective hide intervention process incorporated into beef processing procedures would significantly reduce carcass contamination by E. coli O157:H7.

Longitudinal Study of Escherichia coli O157:H7 in a Beef Cattle Feedlot and Role of High-Level Shedders in Hide Contamination

ABSTRACT The objectives of the study described here were (i) to investigate the dynamics of Escherichia coli O157:H7 fecal and hide prevalence over a 9-month period in a feedlot setting and (ii) to determine how animals shedding E. coli O157:H7 at high levels affect the prevalence and levels of E. coli O157:H7 on the hides of other animals in the same pen. Cattle (n = 319) were distributed in 10 adjacent pens, and fecal and hide levels of E. coli O157:H7 were monitored. When the fecal pen prevalence exceeded 20%, the hide pen prevalence was usually (25 of 27 pens) greater than 80%. Sixteen of 19 (84.2%) supershedder (>104 CFU/g) pens had a fecal prevalence greater than 20%. Significant associations with hide and high-level hide (≥40 CFU/100 cm2) contamination were identified for (i) a fecal prevalence greater than 20%, (ii) the presence of one or more high-density shedders (≥200 CFU/g) in a pen, and (iii) the presence of one or more supershedders in a pen. The results presented here suggest that the E. coli O157:H7 fecal prevalence should be reduced below 20% and the levels of shedding should be kept below 200 CFU/g to minimize the contamination of cattle hides. Also, large and unpredictable fluctuations within and between pens in both fecal and hide prevalence of E. coli O157:H7 were detected and should be used as a guide when preharvest studies, particularly preharvest intervention studies, are designed.

Determination of free chlorine concentrations needed to prevent Escherichia coli O157:H7 cross-contamination during fresh-cut produce wash.

This study was conducted to investigate the effect of free chlorine concentrations in wash water on Escherichia coli O157:H7 reduction, survival, and transference during washing of fresh-cut lettuce. The effectiveness of rewashing for inactivation of E. coli O157:H7 on newly cross-contaminated produce previously washed with solutions containing an insufficient amount of chlorine also was assessed. Results indicate that solutions containing a minimum of 0.5 mg/liter free chlorine were effective for inactivating E. coli O157:H7 in suspension to below the detection level. However, the presence of 1 mg/liter free chlorine in the wash solution before washing was insufficient to prevent E. coli O157:H7 survival and transfer during washing because the introduction of cut lettuce to the wash system quickly depleted the free chlorine. Although no E. coli O157:H7 was detected in the wash solution containing 5 mg/liter free chlorine before washing a mix of inoculated and uninoculated lettuce, low numbers of E. coli O157:H7 cells were detected on uninoculated lettuce in four of the seven experimental trials. When the prewash free chlorine concentration was increased to 10 mg/liter or greater, no E. coli O157:H7 transfer was detected. Furthermore, although rewashing newly cross-contaminated lettuce in 50 mg/liter free chlorine for 30 s significantly reduced (P = 0.002) the E. coli O157:H7 populations, it failed to eliminate E. coli O157:H7 on lettuce. This finding suggests that rewashing is not an effective way to correct for process failure, and maintaining a sufficient free chlorine concentration in the wash solution is critical for preventing pathogen cross-contamination.

Development and Evaluation of an On-Line Hide Decontamination Procedure for Use in a Commercial Beef Processing Plant

The hides of cattle are the source of Escherichia coli O157:H7 that contaminates beef carcasses during commercial beef processing. Therefore, effective interventions that reduce hide contamination should reduce subsequent carcass contamination. The first objective of this study was to identify the most effective reagents for decontamination of beef hides. Cattle hides draped over barrels were used for in vitro experiments to compare the efficacy of washes using 1.6% sodium hydroxide, 4% trisodium phosphate, 4% chlorofoam, or 4% phosphoric acid, each followed by a rinse step using either water or acidified (pH 7.0) chlorine at 200 or 500 ppm. All treatments using a water rinse reduced hide coliform counts by 1.5 to 2.5 log CFU/100 cm2. Compared with water rinses, 200 and 500 ppm acidified chlorine rinses increased efficacy by approximately 1.0 and 2.0 log CFU/100 cm2, respectively. Vacuuming of the treated areas to remove excess liquid improved hide cleanliness by an average of an additional 1.0 log CFU/10...

Development of methods for the recovery of Escherichia coli O157:H7 and Salmonella from beef carcass sponge samples and bovine fecal and hide samples

Culture methods were developed for the concurrent recovery of Escherichia coli O157:H7 and Salmonella from bovine carcass, hide, and fecal samples. Several enrichment conditions were tested for the overall growth of pure cultures; tryptic soy broth for 2 h at 25 degrees C and then for 6 h at 42 degrees C was the protocol selected for use. Immunomagnetic separation (IMS) was incorporated for sensitivity and selectivity, along with a post-IMS enrichment for the recovery of Salmonella as recommended by the manufacturer. Selective agars for plating after IMS were chosen on the basis of ease of target colony identification. Sorbitol MacConkey agar supplemented with cefixime and potassium tellurite and Rainbow agar supplemented with novobiocin and potassium tellurite were chosen for the recovery of E. coli O157:H7. Brilliant green agar with sulfadiazine and Hektoen enteric agar supplemented with novobiocin were selected for the recovery of Salmonella. The resulting methods were evaluated along with standard or previously used methods for the recovery of E. coli O157:H7 and Salmonella from bovine hide and fecal samples and carcass sponge samples. The Meats Research Unit (MRU) methods performed at least as well as the established methods, except that a secondary enrichment in tetrathionate (TT) broth prior to IMS was required for the optimal recovery of Salmonella from feces. Thus, the MRU and MRU-TT methods are effective in the recovery of both E. coli O157:H7 and Salmonella from a single bovine carcass, hide, or fecal sample.

Treatments Using Hot Water Instead of Lactic Acid Reduce Levels of Aerobic Bacteria and Enterobacteriaceae and Reduce the Prevalence of Escherichia coli O157:H7 on Preevisceration Beef Carcasses †

Lactic acid has become the most commonly used organic acid for treatment of postevisceration beef carcasses. Many processors have also implemented 2% lactic acid washes on preevisceration carcasses. We previously demonstrated that hot water washing and steam vacuuming are effective carcass interventions. Because of the effectiveness of hot water, we compared its use with that of lactic acid as a preevisceration wash in a commercial setting. A commercial hot water carcass wash cabinet applying 74 degrees C (165 degrees F) water for 5.5 s reduced both aerobic plate counts and Enterobacteriaceae counts by 2.7 log CFU/100 cm2 on preevisceration carcasses. A commercial lactic acid spray cabinet that applied 2% L-lactic acid at approximately 42 degrees C (105 to 110 degrees F) to preevisceration carcasses reduced aerobic plate counts by 1.6 log CFU/100 cm2 and Enterobacteriaceae counts by 1.0 log CFU/100 cm2. When the two cabinets were in use sequentially, i.e., hot water followed by lactic acid, aerobic plate counts were reduced by 2.2 log CFU/100 cm2 and Enterobacteriaceae counts were reduced by 2.5 log CFU/100 cm2. Hot water treatments reduced Escherichia coli O157:H7 prevalence by 81%, and lactic acid treatments reduced E. coli O157:H7 prevalence by 35%, but the two treatments in combination produced a 79% reduction in E. coli O157:H7, a result that was no better than that achieved with hot water alone. These results suggest that hot water would be more beneficial than lactic acid for decontamination of preevisceration beef carcasses.

A pilot plant scale evaluation of a new process aid for enhancing chlorine efficacy against pathogen survival and cross-contamination during produce wash

Developing food safety intervention technology that can be readily adopted by the industry often requires test conditions that match as closely as possible to those of commercial food processing operations; yet biosafety risks inherent in pathogen studies constrain most experiments to laboratory settings. In this study, we report the first semi-commercial pilot-scale evaluation of a new process aid, T128, for its impact on enhancing the antimicrobial efficacy of chlorinated wash water against pathogen survival and cross-contamination. A non-pathogenic, BSL-1, strain of Escherichia coli O157:H7 was inoculated onto freshly harvested baby spinach leaves and washed with large amounts of freshly cut un-inoculated iceberg lettuce shreds in wash water with free chlorine periodically replenished, in the presence or absence of T128. Changes in water quality and pathogen survival and cross-contamination were monitored at every 2 min intervals for up to 36 min for each treatment during the wash operation. Results indicated that the use of T128 did not significantly (P>0.05) influence the rate of wash water deterioration, nor the pathogen populations remaining on the inoculated spinach leaves. However, in the absence of T128 (control), survival of E. coli O157:H7 in wash water and cross-contamination of un-inoculated lettuce frequently occurred when free chlorine in solution dropped below 1mg/l during the wash process. In contrast, the use of T128 significantly reduced the occurrence of E. coli O157:H7 surviving in wash water and of cross-contamination to un-inoculated shredded iceberg lettuce under the same operational conditions, suggesting that the application of T128 in a chlorine-based fresh produce sanitization system could increase the safety margin of process control on fresh-cut operations.

Dynamic Effects of Free Chlorine Concentration, Organic Load, and Exposure Time on the Inactivation of Salmonella, Escherichia coli O157:H7, and Non-O157 Shiga Toxin–Producing E. coli†

This study evaluated the dynamic effects of free-chlorine (FC) concentration, contact time, and organic load on the inactivation of Salmonella, Escherichia coli O157:H7, and non-O157 Shiga toxin-producing E. coli (STEC) in suspension. Bacterial cells from four strains each of Salmonella, E. coli O157:H7, and non-O157 STEC were inoculated separately or as a multistrain cocktail into solutions with varying FC concentrations. Lettuce or tomato extract was used to simulate the organic matter present during commercial fresh and fresh-cut produce wash operations. After exposure to FC for various lengths of time, the bacterial survival and water-quality changes were determined. In the absence of organic matter in a wash solution, pathogen inactivation is primarily a function of initial FC concentration (P < 0.0001), exposure time (P < 0.0001), and pathogen strains (P < 0.0001). In general, an over 4.5-log CFU/ml pathogen reduction was found after exposure to >0.5 mg/liter FC for over 30 s, or to >1.0 mg/liter FC for over 5 s. When the combination of FC concentration and contact time were less than or equal to the above conditions, survival of pathogens was strain dependant and ranked as: Salmonella > E. coli O157:H7 > non-O157 STEC. When organic matter was present in the wash solution, pathogen inactivation efficacy was specifically dependent on the residual FC concentration, which directly relates to both the initial FC concentration and the organic load. Prevention of pathogen survival in chlorinated produce wash solutions can be achieved by maintaining sufficient FC concentration and reducing the accumulation of organic matter.

Methods for Recovering Escherichia coli O157:H7 from Cattle Fecal, Hide, and Carcass Samples: Sensitivity and Improvements †

The Meats Research Unit (MRU) methods, developed by MRU scientists of the U.S. Meat Animal Research Center, have been used to study the prevalence of Escherichia coli O157:H7 in cattle carcass, hide, and fecal samples. The sensitivity of these methods for recovery of injured E. coli O157:H7 cells from inoculated and uninoculated samples was determined, and potential improvements to these methods were evaluated. When using the conventional MRU methods, 91% of the pre-evisceration carcass samples tested positive for E. coli O157:H7 when inoculated with 5 to 10 CFU, 100% of hide samples tested positive for E. coli O157:H7 when inoculated with 30 to 50 CFU, and 96% of the fecal samples produced positive results when inoculated with 300 to 400 CFU per 10 g. The addition of a phosphate buffer to the tryptic soy broth enrichment improved recovery of E. coli O157:H7 from feces. Using the modified enrichment, 92% of the samples were identified as positive when inoculated with 10 to 30 CFU per 10 g. Substituting a commercially available wash buffer for the phosphate-buffered saline (PBS) plus Tween 20 wash buffer during immunomagnetic separation of hide samples improved recovery of the target organism at lower inoculum concentrations. When comparing uninoculated samples, substituting a PBS buffer plus a zwitterionic detergent for PBS plus Tween 20 also had a positive effect on recovery of E. coli O157:H7 from hide samples. Data presented here indicate that the MRU methods are highly effective at recovering injured E. coli O157:H7 from fecal, hide, and beef carcass samples; however, modifications can be added to increase the sensitivity.