Effect of xylitol on adhesion of Salmonella Typhimurium and Escherichia coli O157:H7 to beef carcass surfaces

Effects of 10% xylitol (a five-carbon sugar alcohol) on adhesion of Escherichia coli O157:H7 and Salmonella Typhimurium to meat surfaces were examined with three approaches. First, beef outside round was inoculated with rifampin-resistant E. coli O157:H7 and Salmonella Typhimurium dispersed in xylitol or peptone solution. Samples were rinsed with water or not rinsed in a 2 x 2 factorial arrangement. No interaction existed between inoculum and rinsing treatments (P > 0.84). Incubation in xylitol had minimal impact on pathogen adhesion (P > 0.76); however, rinsing reduced pathogen cell counts (P < 0.01). Second, meat samples were treated with water, xylitol, or no rinse; inoculated with pathogens dispersed in peptone solution (8.6 log CFU/ml for each pathogen); and then treated with water, xylitol, or no rinse in a 3 x 3 factorial arrangement. No interactions were observed (P > 0.50). Postinoculation rinsing reduced pathogen loads (P < 0.01) without difference between water and xylitol (P > 0.64). Third, carcass surfaces inoculated with pathogens (5.5 log CFU/cm2) were treated with 35 degrees C water wash, 2.5% L-lactic acid spray, 10% xylitol spray, lactic acid plus xylitol, or hot water plus xylitol. Lactic acid treatments reduced Salmonella Typhimurium at 0 h (P < 0.01) and 24 h (P < 0.02). Hot water treatments tended to reduce Salmonella Typhimurium at 0 h (P < 0.07). Xylitol did not reduce pathogens (P > 0.62) or increase effectiveness of other treatments. Xylitol does not influence E. coli O157:H7 and Salmonella Typhimurium adhesion to meat surfaces.     

Evaluation of peroxyacetic acid as a post-chilling intervention for control of Escherichia coli O157:H7 and Salmonella Typhimurium on beef carcass surfaces

Four experiments were conducted to test the efficacy of peroxyacetic acid as a microbial intervention on beef carcass surfaces. In these experiments, beef carcass surfaces were inoculated with fecal material (no pathogens) or fecal material containing rifampicin-resistant Escherichia coli O157:H7 and Salmonella Typhimurium. Inoculated surfaces were subjected to a simulated carcass wash with and without 2% l-lactic acid treatment before chilling. In Experiments 1 and 2, the chilled carcass surfaces were sprayed with peroxyacetic acid (200 ppm; 43°) for 15 s. Peroxyacetic acid had no effect on microbial counts of any organism measured on these carcass surfaces. However, lactic acid reduced counts of E. coli Type I (1.9log(10) CFU/cm(2)), coliforms (3.0log(10) CFU/cm(2)), E. coli O157:H7 (2.7log(10) CFU/cm(2)), and S. Typhimurium (2.8log(10) CFU/cm(2)) entering the chilling cooler and prevented growth during the chilling period. In Experiment 3, peroxyacetic acid at different concentrations (200, 600, and 1000 ppm) and application temperatures (45 and 55 °C) were used to investigate its effectiveness in killing E. coli O157:H7 and S. Typhimurium compared to 4% l-lactic acid (55 °C). Application temperature did not affect the counts of either microorganism. Peroxyacetic acid concentrations up to 600 ppm had no effect on these microorganisms. Concentrations of 1000 ppm reduced E. coli O157:H7 and S. Typhimurium by up to 1.7 and 1.3log(10) CFU/cm(2), respectively. However, 4% lactic acid reduced these organisms by 2.7 and 3.4log(10) CFU/cm(2), respectively. In Experiment 4, peroxyacetic acid (200 ppm; 43 °C) was applied to hot carcass surfaces. This treatment caused a 0.7log(10) CFU/cm(2) reduction in both E. coli O157:H7 and S. Typhimurium. The collective results from these experiments indicate that peroxyacetic acid was not an effective intervention when applied to chilled inoculated carcass piece surfaces.     

Ozone treatment for reduction of Escherichia coli 0157:H7 and Salmonella serotype typhimurium on beef carcass surfaces

The effectiveness of an aqueous ozone treatment in reducing Escherichia coli O157:H7 and Salmonella serotype Typhimurium on hot carcass surfaces was determined with the use of a model carcass spray cabinet. Carcass surface regions were removed from carcasses and inoculated with feces containing 10(6) to 10(7) CFU each of E. coli O157:H7 and Salmonella Typhimurium per g and were then exposed to a water wash or to a water wash followed by a sanitizing ozone treatment. Water washes were applied at 28 degrees C beginning at a pressure of 10 lb/in2 and gradually increasing to 400 lb/in2. Ozone treatment was carried out by spraying surfaces with an aqueous ozone solution (80 lb/in2 at 28 degrees C) containing 95 mg of ozone per liter. Pathogen reductions achieved with ozone treatment were not significantly different from those achieved with a water wash alone. In addition, ozone treatment did not reduce E. coli O157:H7 or Salmonella Typhimurium contamination that was spread over the carcass surface as a result of the water wash. Under the conditions of this study, the aqueous ozone treatment applied resulted in no significant improvement over a water wash in reducing pathogens on beef carcass surfaces.     

Bactericidal effect of sodium chlorate on Escherichia coli O157:H7 and Salmonella typhimurium DT104 in rumen contents in vitro

Escherichia coli O157:H7 and Salmonella Typhimurium DT104 are important foodborne pathogens affecting the beef and dairy industries and strategies are sought to rid these organisms from cattle at slaughter. Both pathogens possess respiratory nitrate reductase that also reduces chlorate to the lethal chlorite ion. Because most anaerobes lack respiratory nitrate reductase, we hypothesized that chlorate may selectively kill E. coli O157:H7 and Salmonella Typhimurium DT104 but not potentially beneficial anaerobes. In support of this hypothesis, we found that concentrations of E. coli O157:H7 and Salmonella Typhimurium DT104 were reduced from approximately 1,000,000 colony forming units (CFU) to below our level of detection (< or = 10 CFU) following in vitro incubation (24 h) in buffered ruminal contents (pH 6.8) containing 5 mM added chlorate. In contrast, chlorate had little effect on the most probable number (mean +/- SD) of total culturable anaerobes (ranging from 9.9 +/- 0.72 to 10.7 +/- 0.01 log10 cells/ml). Thus, chlorate was bactericidal to E. coli O157:H7 and Salmonella Typhimurium DT104 but not to potentially beneficial bacteria. The bactericidal effect of chlorate was concentration dependent (less at 1.25 mM) and markedly affected by pH (more bactericidal at pH 6.8 than pH 5.6).     

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.     

Inactivation of Escherichia coli O157:H7 and Salmonella typhimurium DT 104 on alfalfa seeds by levulinic acid and sodium dodecyl sulfate

Studies were conducted to determine the best concentration and exposure time for treatment of alfalfa seeds with levulinic acid plus sodium dodecyl sulfate (SDS) to inactivate Escherichia coli O157:H7 and Salmonella without adversely affecting seed germination. Alfalfa seeds inoculated with a five-strain mixture of E. coli O157:H7 or Salmonella Typhimurium were dried in a laminar flow hood at 21°C for up to 72 h. Inoculated alfalfa seeds dried for 4 h then treated for 5 min at 21°C with 0.5% levulinic acid and 0.05% SDS reduced the population of E. coli O157:H7 and Salmonella Typhimurium by 5.6 and 6.4 log CFU/g, respectively. On seeds dried for 72 h, treatment with 0.5% levulinic acid and 0.05% SDS for 20 min at 21°C reduced E. coli O157:H7 and Salmonella Typhimurium populations by 4 log CFU/g. Germination rates of alfalfa seeds treated with 0.5% levulinic acid plus 0.05% SDS for up to 1 h at 21°C were compared with a treatment of 20,000 ppm of calcium hypochlorite or tap water only. Treatment of alfalfa seeds with 0.5% levulinic acid plus 0.05% SDS for 5 min at 21°C resulted in a >3.0-log inactivation of E. coli O157:H7 and Salmonella.     

Reduction of Escherichia coli O157:H7 and Salmonella typhimurium on beef carcass surfaces using acidified sodium chlorite.

The efficacy of a phosphoric acid-activated acidified sodium chloride (PASC) spray and a citric acid-activated acidified sodium chlorite (CASC) spray applied at room temperature (22.4 to 24.7 degrees C) in combination with a water wash was compared with that of a water wash only treatment for reduction of Escherichia coli O157:H7 and Salmonella Typhimurium inoculated onto various hot-boned individual beef carcass surface regions (inside round, outside round, brisket, flank, and clod). Initial counts of 5.5 and 5.4 log CFU/cm2 were obtained after inoculation with E. coli O157:H7 and Salmonella Typhimurium, respectively. Initial numbers for both pathogens were reduced by 3.8 to 3.9 log cycles by water wash followed by PASC spray and by 4.5 to 4.6 log cycles by water wash followed by CASC spray. The sprays consisted of applying 140 ml of the appropriate sanitizing solution for 10 s at 69 kPa. Corresponding reduction values obtained by water wash alone were 2.3 log. The performance of CASC appeared to be consistently better than that of PASC. In general, no effect of the carcass surface region was observed on the log reductions for either pathogen, except for the inside round, which consistently had lower reductions. Both PASC and CASC were capable of effectively reducing pathogens spread to areas beyond the initial contaminated area of the cuts to levels close to or below the counting method detection limit (0.5 log CFU/cm2). However, 30 to 50% of the carcasses treated by these antimicrobial solutions still yielded countable colonies. Results of this study indicate that acidified sodium chlorite sprays are effective for decontaminating beef carcass surfaces.     

Occurrence of Escherichia coli O157:H7 and other enterohemorrhagic Escherichia coli in the environment

Enterohemorrhagic Escherichia coli (EHEC) (O157 and other serotypes) are zoonotic pathogens linked with severe human illnesses. The main virulence factors of EHEC are the Shiga toxins, among others. Most of the genes coding for these toxins are bacteriophage-encoded. Although ruminants are recognized as their main natural reservoir, water has also been documented as a way of transmission of EHEC. E. coli O157:H7 and other EHEC may contaminate waters (recreational, drinking or irrigation waters) through feces from humans and other animals. Indeed, the occurrence of EHEC carrying the stx2 gene in raw municipal sewage and animal wastewater from several origins has been widely documented. However, the evaluation of the persistence of naturally occurring EHEC in the environment is still difficult due to methodological problems. Methods proposed for the detection and isolation of stx-encoding bacteria, ranging from the classic culture-based methods to molecular approaches, and their application in the environment, are discussed here. Most virulence factors associated with these strains are linked to either plasmids or phages, and consequently they are likely to be subject to horizontal gene transfer between species or serotypes. Moreover, the presence of infectious stx-phages isolated as free particles in the environment and their high persistence in water systems suggest that they may contribute to the spread of stx genes, as they are directly involved in the emergence of new pathogenic strains, which might have important health consequences.     

Growth of Escherichia coli O157:H7, Salmonella typhimurium DT104, and Listeria monocytogenes in dark cutting beef at 10 or 22 degrees C.

An experiment was conducted to determine the effects of the dark, firm, and dry (DFD) condition of beef on growth of the foodborne pathogens Escherichia coli O157:H7, Salmonella Typhimurium DT104, and Listeria monocytogenes Scott A in ground beef. Longissimus muscles from a DFD carcass (pH = 6.45) and normal carcass (N; pH = 5.64) were ground and samples obtained (100 and 0% DFD, respectively). Equal amounts of the 0 and 100% DFD ground samples were mixed to obtain 50% DFD samples. Inoculated 0, 50, and 100% DFD samples were packaged into oxygen-permeable overwrap and stored at 10 degrees C for E. coli O157:H7, Salmonella Typhimurium DT104, and L. monocytogenes Scott A or at 22 degrees C for E. coli O157:H7. Growth characteristics of E. coli O157:H7, Salmonella Typhimurium DT104, and L. monocytogenes Scott A did not differ (P > 0.05) between 0 and 100% DFD. Results indicated that the DFD beef used in this study was no more susceptible to growth of E. coli O157:H7, Salmonella Typhimurium, or L. monocytogenes Scott A than N beef.     

Growth rates of Salmonella and Escherichia coli O157:H7 in irradiated beef.

Ground beef was irradiated to 0, 2, or 4 kGy and then inoculated with a mixed culture of four serotypes of salmonellae or five strains of Escherichia coli O157:H7. The ground beef was stored at either 15 or 25 degrees C, and the growth of the inoculated bacteria was monitored over time. Growth parameters were determined for both the salmonellae and the E. coli O157:H7 using the Gompertz equation. There was no significant difference in lag phase duration or generation time, irrespective of the dose to which the ground beef had previously been exposed. Furthermore, the lag phase durations and generation times determined in this study did not differ significantly from previously published values. This suggests that, although irradiation eliminates a significant portion of the spoilage microflora in ground beef, the absence of this microflora provides no competitive advantage to the growth of salmonellae or E. coli O157:H7 in ground beef.     

Evaluation of peroxyacetic acid as a potential pre-grinding treatment for control of Escherichia coli O157:H7 and Salmonella Typhimurium on beef trimmings

Peroxyacetic acid was evaluated in four separate trials for ability to reduce populations of Escherichia coli O157:H7 and Salmonella serotype Typhimurium on fresh beef trim. Trial 1 examined the effectiveness of peroxyacetic acid on individual pieces of fresh beef trim. Trial 2 evaluated the efficacy of peroxyacetic acid at low levels of contamination on batches of fresh beef trim. Trial 3 studied a washing effect of water. Lastly, Trial 4 compared the effectiveness of peroxyacetic acid to lactic acid. At various inoculation levels, peroxyacetic acid reduced populations of both pathogens by approximately 1.0log(10)CFU/cm(2) on fresh beef trim. Trial 3 showed that approximately half of the reductions found in Trials 1 and 2 were due to a washing effect of the water dip. In addition, as shown in Trial 1, increases in concentrations (>200ppm) did not significantly increase log(10) reductions of both pathogens. Following a water dip in Trial 4, peroxyacetic acid caused a reduction of 0.7log(10)CFU/cm(2) in E. coli O157:H7 and 1.0log(10)CFU/cm(2) in Salmonella Typhimurium, whereas lactic acid caused a reduction of 1.3log(10)CFU/cm(2) in E. coli O157:H7 and 2.1log(10)CFU/cm(2) in S. Typhimurium following the water dip. These results show that peroxyacetic acid was not more effective than 2% l-lactic acid in reducing pathogens on fresh beef trim.     

Experimental use of a gas sensor-based instrument for differentiation of Escherichia coli O157:H7 from non-O157:H7 Escherichia coli field isolates

The rapid and economical detection of human pathogens in animal and food production systems would enhance food safety efforts. An instrument based on gas sensors coupled with an artificial neural network (ANN) was developed for the detection of and differentiation between laboratory isolates of Escherichia coli O157:H7 and non-O157:H7 E. coli. The purpose of this study was to use field isolates of E. coli to further evaluate the sensor system. This gas sensor-based, computer-controlled detection system was used to monitor gas emissions from 12 isolates of E. coli O157:H7 and 8 non-O157:H7 E. coli isolates. A standard concentration of each isolate was grown in 10 ml of nutrient broth at 37 degrees C for 16 h, and gas sampling was carried out every 5 min. Readings were continuously plotted to generate gas signatures. A back-propagation ANN algorithm was used to interpret the gas patterns. By analysis of the response of the ANN, the sensitivity and specificity of the instrument were calculated. Detectable differences between the gas signatures of the E. coli O157:H7 isolates and the non-O157:H7 isolates were observed. The instruments degree of sensitivity was high for E. coli O157:H7 isolates, but a lower degree of accuracy was observed for non-O157:H7 isolates because of increased strain variation. The sensitivity of the detection system was improved by the normalization of the data generated from the gas sensors. Because of its ability to detect differences in gas patterns, this instrument has a broad range of potential food safety applications.     

Thermal Inactivation of Salmonella spp., Salmonella typhimurium DT104, and Escherichia coli 0157:H7 in Ground Beef

ABSTRACT: In 19.1% fat ground beef, Escherichia coli 0157:H7 was less heat- resistant at ≥58°C than the Salmonella typhimurium DT104 and Salmonella senftenberg , but at 55°C the D value was similar to DT104 strains and higher than an eight-strain Salmonella cocktail. Inactivation of E. coli 0157:H7 was more temperature-dependent than the cocktail and DT104 strains. E. coli and DT104 strains were more heat-resistant in beef containing 19% fat than 4.8% fat. The cocktail was more thermally stable in stationary as compared to log phase. Freezing of inoculated raw meat decreased heat resistance of the cocktail. The pathogenic strain, growth phase of the organism, state of the meat (fresh or frozen) and meat composition must be considered when designing protocols to verify thermal processes.     

Survival of enterohemorrhagic Escherichia coli O157:H7 in retail mustard

Escherichia coli O157:H7 survival in acid foods such as unpasteurized apple cider and fermented sausage is well documented. Researchers have determined that E. coli O157:H7 can survive in refrigerated acid foods for weeks. The potential of acid foods to serve as a vector of E. coli O157:H7 foodborne illness prompted this study to determine the fate of this organism in retail mustard containing acetic acid when stored at room and refrigerated temperatures. Various retail brands of dijon, yellow, and deli style mustard, pH ranging from 3.17 to 3.63, were inoculated individually with three test strains of E. coli O157:H7. Samples were inoculated with approximately 1.0 x 10(6) CFU/g, incubated at room (25+/-2.5 degrees C) and refrigerated (5+/-3 degrees C) temperatures, and assayed for surviving test strains at predetermined time intervals. An aliquot was appropriately diluted and plated using sorbitol MacConkey agar (SMAC). When the test strain was not recoverable by direct plating, the sample was assayed by enrichment in modified tryptic soy broth and recovered using SMAC. Growth of E. coli O157:H7 test strains was inhibited in all retail mustard styles. E. coli O157:H7 was not detected in dijon style mustard beyond 3 h at room and 2 days at refrigerated temperatures. Survival in yellow and deli style mustard was not detected beyond 1 h. Overall, test strain survival was greater at refrigerated than room temperature. Retail mustard demonstrated the ability to eliminate effectively any chance contamination by this organism within hours to days, suggesting that these products are not a likely factor in E. coli O157:H7 foodborne illness.     

GC-MS based metabolomics for rapid simultaneous detection of Escherichia coli O157:H7, Salmonella Typhimurium, Salmonella Muenchen, and Salmonella Hartford in ground beef and chicken

A metabolomic-based method for rapid detection of Escherichia coli O157:H7, Salmonella Hartford, Salmonella Typhimurium, and Salmonella Muenchen in nonselective media was developed. All pathogenic bacteria were grown in tryptic soy broth (TSB) at 37 °C followed by metabolite quantification at 2-h intervals for 24 h. Results were compared with the metabolite profiles similarly obtained with E. coli K12, Pseudomonas aeruginosa, Staphylococcus aureus, Saccharomyces cereviseae, and Aspergillus oryzae grown individually or as a cocktail under the same conditions. Principal component analysis (PCAS) discriminated pathogenic microorganisms grown in TSB. Metabolites responsible of PCAS classification were dextrose, cadaverine, the aminoacids L-histidine, glycine, and L-tyrosine, as well as the volatiles 1-octanol, 1-propanol, 1butanol, 2-ethyl-1-hexanol, and 2,5-dimethyl-pyrazine. Partial least square (PLS) models based on the overall metabolite profile of each bacteria were able to detect the presence of Escherichia coli O157:H7 and Salmonella spp. at levels of approximately 7 ± 2 CFU/25 g of ground beef and chicken within 18 h.     

Efficacy of Neutral pH Electrolyzed Water in Reducing Escherichia coli O157:H7 and Salmonella Typhimurium DT 104 on Fresh Produce Items using an Automated Washer at Simulated Food Service Conditions

The objective of this study was to determine the efficacy of neutral pH electrolyzed (NEO) water (155 mg/L free chlorine, pH 7.5) in reducing Escherichia coli O157:H7 and Salmonella Typhimurium DT 104 on romaine lettuce, iceberg lettuce, and tomatoes washed in an automated produce washer for different times and washing speeds. Tomatoes and lettuce leaves were spot inoculated with 100 μL of a 5 strain cocktail mixture of either pathogen and washed with 10 or 8 L of NEO water, respectively. Washing lettuce for 30 min at 65 rpm led to the greatest reductions, with 4.2 and 5.9 log CFU/g reductions achieved for E. coli O157:H7 and S. Typhimurium respectively on romaine, whereas iceberg lettuce reductions were 3.2 and 4.6 log CFU/g for E. coli O157:H7 and S. Typhimurium respectively. Washing tomatoes for 10 min at 65 rpm achieved reductions greater than 8 and 6 log CFU/tomato on S. Typhimurium and E. coli O157:H7 respectively. All pathogens were completely inactivated in NEO water wash solutions. No detrimental effects on the visual quality of the produce studied were observed under all treatment conditions. Results show the adoption of this washing procedure in food service operations could be useful in ensuring produce safety.     

Fate of Listeria monocytogenes, Salmonella typhimurium DT104, and Escherichia coli O157:H7 in Labneh as a pre- and postfermentation contaminant

Commercially pasteurized milk (approximately 2% milkfat) was heated at 85 to 87 degrees C/30 min, inoculated to contain 2,000 to 6,000 CFU/ml of Listeria monocytogenes, Salmonella typhimurium DT104, or Escherichia coli O157:H7, cultured at 43 degrees C for 4 h with a 2.0% (wt/wt) commercial yogurt starter culture, stored 12 to 14 h at 6 degrees C, and centrifuged to obtain a Labneh-like product. Alternatively, traditional salted and unsalted Labneh was prepared using a 3.0% (wt/wt) starter culture inoculum, similarly inoculated after manufacture with the aforementioned pathogens, and stored at 6 degrees C and 20 degrees C. Throughout fermentation, Listeria populations remained unchanged, whereas numbers of Salmonella increased 0.33 to 0.47 logs during the first 2 h of fermentation and decreased thereafter. E. coli populations increased 0.46 to 1.19 logs during fermentation and remained that these levels during overnight cold storage. When unsalted and salted Labneh were inoculated after manufacture, Salmonella populations decreased >2 logs in all samples after 2 days, regardless of storage temperature, with the pathogen no longer detected in 4-day-old samples. Numbers of L. monocytogenes decreased from 2.48 to 3.70 to < 1.00 to 1.95 logs after 2 days with the pathogen persisting up to 15 days in one lot of salted/unsalted Labneh stored at 6 degrees C. E. coli O157:H7 populations decreased from 3.39 to 3.7 to < 1.00 to 2.08 logs during the first 2 days, with the pathogen no longer detected in any 4-day-old samples. Inactivation rates for all three pathogens in Labneh were unrelated to storage temperature or salt content. Unlike L. monocytogenes that persisted up to 15 days in Labneh, rapid inactivation of Salmonella typhimurium DT104 and E. coli O157:H7 suggests that these emerging foodborne pathogens are of less public health concern in traditional Labneh.     

Fate of Shiga toxin-producing O157:H7 and non-O157:H7 Escherichia coli cells within blade-tenderized beef steaks after cooking on a commercial open-flame gas grill

We compared the fate of cells of both Shiga toxin-producing Escherichia coli O157:H7 (ECOH) and Shiga toxin-producing non-O157:H7 E. coli (STEC) in blade-tenderized steaks after tenderization and cooking on a gas grill. In phase I, beef subprimal cuts were inoculated on the lean side with about 5.5 log CFU/g of a five-strain mixture of ECOH or STEC and then passed once through a mechanical blade tenderizer with the lean side facing up. In each of two trials, 10 core samples were removed from each of two tenderized subprimals and cut into six consecutive segments starting from the inoculated side. Ten total cores also were obtained from two nontenderized (control) subprimals, but only segment 1 (the topmost segment) was sampled. The levels of ECOH and STEC recovered from segment 1 were about 6.0 and 5.3 log CFU/g, respectively, for the control subprimals and about 5.7 and 5.0 log CFU/g, respectively, for the tenderized subprimals. However, both ECOH and STEC behaved similarly in terms of translocation, and cells of both pathogen cocktails were recovered from all six segments of the cores obtained from tenderized subprimals, albeit at lower levels in segments 2 to 6 than those found in segment 1. In phase II, steaks (2.54 and 3.81 cm thick) cut from tenderized subprimals were subsequently cooked (three steaks per treatment) on a commercial open-flame gas grill to internal temperatures of 48.9, 54.4, 60.0, 65.6, and 71.1°C. Regardless of temperature or thickness, we observed 2.0- to 4.1-log and 1.5- to 4.5-log reductions in ECOH and STEC levels, respectively. Both ECOH and STEC behaved similarly in response to heat, in that cooking eliminated significant numbers of both pathogen types; however, some survivors were recovered due, presumably, to uneven heating of the blade-tenderized steaks.     

Dispersion and survival of Escherichia coli O157:H7 and Salmonella Typhimurium during the production of marinated beef inside skirt steaks and tri-tip roasts

To determine the depth of pathogen dispersion and the ability of pathogens to survive in enhanced beef products and spent marinade, beef inside skirt steaks and tri-tip roasts were vacuum tumbled with two commercial marinades. The marinades were inoculated with Escherichia coli O157:H7 and Salmonella Typhimurium, resulting in an approximate count of 5.2 log CFU/ml. Both inside skirt steaks and tri-tip roasts were vacuum tumbled for 1 h and sampled immediately after tumbling (day 0), or were vacuum packaged, stored (ca. 4°C), and sampled on days 7 and 14. Samples of the spent marinade were taken after tumbling (day 0) and on days 3 and 7. For both marinades, Salmonella Typhimurium and E. coli O157:H7 were dispersed throughout the inside skirt steaks during vacuum tumbling. Although Salmonella Typhimurium and E. coli O157:H7 for the skirt steaks were still detectable after 14 days of storage, the log values were lower than those on days 0 and 7. For the tri-tip roasts, the pathogen distribution varied, depending on the thickness of the roasts, and pathogens were detectable on days 0, 7, and 14. The spent marinade sampled on days 0, 3, and 7 showed that the pathogens survived at refrigerated temperatures. Because pathogens can transfer to the interior of beef inside skirt steaks and tri-tip roasts when vacuum tumbled with contaminated marinade and survived during refrigerated storage, establishments should consider the potential food safety risks associated with reuse of marinade during the production of vacuum-tumbled beef products.