Category Archives: E.coli O157

Research – Comparison of Antimicrobial Treatments Applied via Conventional or Handheld Electrostatic Spray To Reduce Shiga Toxin–Producing Escherichia coli on Chilled Beef Outside Rounds

Journal of Food Protection

ABSTRACT

The purpose of this study was to compare the efficacy of different antimicrobial interventions applied via either conventional spray (CS) or handheld electrostatic spray (ESS) to reduce Shiga toxin–producing Escherichia coli (STEC) on fresh beef surfaces. Hot-boned outside rounds (ORs) were inoculated within 1 h after harvest with a cocktail of eight isolates consisting of 8 O157 and non-O157 serogroups of STEC (STEC8). ORs were hung on sterile meat hooks at 4°C for 36 h to simulate a contaminated full carcass side in the chiller. ORs were then treated with lactic acid (LA; 4.5%, w/v), 3.0% lauric arginate ester (LAE), 0.8% cetylpyridinium chloride, 200 mg/L peracetic acid, 3 mg/L chlorine dioxide, 5 mg/L ClO2, or tap water by using CS or ESS. Temperatures of LA and peracetic acid were set at 55 and 42°C before spraying, whereas all other solutions were applied at room temperature (25°C). Pretreatment and posttreatment STEC8-inoculated beef tissue samples were aseptically collected to evaluate the efficacy of interventions by application method (CS or ESS). LA applied with CS achieved the greatest reduction in STEC8 numbers (3.3 log CFU/cm2) compared with all other treatments: 0.2 log CFU/cm2 (tap water) to 2.3 log CFU/cm2 (LAE). Only for LA did a significant difference arise in mean STEC8 reductions between CS and ESS applications (3.2 versus 1.7 log CFU/cm2, respectively). Among the treatments applied with ESS, LAE produced the greatest reduction of STEC8. Antimicrobial interventions applied via conventional wand or cabinet-applied technologies can reduce the O157 and non-O157 STEC on fresh beef carcass surfaces, reducing transmission to beef consumers.

HIGHLIGHTS
  • We found no advantage in the use of electrostatic spray to reduce STEC8 on cold beef.

  • Greatest reductions in STEC8 were achieved by lactic acid with conventional spray.

  • Lauric arginate ester was the second best antimicrobial agent at reducing STEC8.

  • Lactic acid reduced pH on the beef surface significantly.

  • There was no effect of antimicrobial solution on temperature increase on beef outside rounds.

Research – Effects of Package Atmosphere and Storage Conditions on Minimizing Risk of Escherichia coli O157:H7 in Packaged Fresh Baby Spinach

Journal of Food Protection

ABSTRACT

Packaged fresh spinach has been associated with outbreaks of illness caused by Escherichia coli O157:H7. The purpose of this study was to assess the behavior of E. coli O157:H7 in packaged baby spinach in response to storage conditions of temperature and package atmosphere and including effects of inoculation level, spinach leaf damage (cut leaves), internalized or leaf surface contamination, exposure to hypochlorite sanitizer, and package size. Behavior of E. coli O157:H7 inoculated at 2 and 4 log CFU/g on spinach packaged in polymer bags composed of a two-layer laminate (polypropylene and polyethylene) and stored under atmospheres of 20% O2–3% CO2 and 0% O2–15% CO2 (aerobic and anaerobic, respectively) was assessed at 5, 7, 12, and 15°C for up to 14 days. Growth kinetics were calculated using DMFit software. Temperature decreases progressively diminished growth or survival of the pathogen, and an aerobic package atmosphere resulted in longer lag times (4 to 6 days) and lower population levels (0.2 to 1.4 log CFU/g) compared with the anaerobic atmosphere at 15°C. Internalized contamination, leaf cuts, or exposure to 100 ppm of hypochlorite did not result in changes in pathogen behavior compared with controls; however, a growth minimization trend consisting of longer lag times and lower population levels was repeatedly observed in the aerobic compared with the anaerobic package atmospheres. In contrast, growth of indigenous mesophiles and Enterobacteriaceae was unaffected by package atmosphere. Spinach stored at 5 to 7°C in two sizes (5 and 16 oz) of polyethylene terephthalate clamshell packages with ambient air atmospheres was more likely to progress to lower-oxygen conditions in 16-oz compared with 5-oz packages after 7 days of storage (P < 0.05). Practices to maintain aerobic conditions within the package, as well as storage of the package at low temperature, are ways to limit growth of E. coli O157:H7 in packaged spinach.

HIGHLIGHTS
  • Cold aerobic conditions limited survival of E. coli O157:H7 in packaged spinach.

  • Low-oxygen atmosphere increased pathogen risk in temperature-abused packages.

  • Internalization, leaf cuts, and hypochlorite stress did not increase pathogen risk.

  • Large spinach packages trended toward lower-oxygen conditions more than small packages.

  • Maintaining cold aerobic conditions can limit pathogen risk in packaged spinach.

Research – Growth of Salmonella and Other Foodborne Pathogens on Inoculated Inshell Pistachios during Simulated Delays between Hulling and Drying

Journal of Food Protection

ABSTRACT

During harvest, pistachios are hulled, separated in water into floater and sinker streams (in large part on the basis of nut density), and then dried before storage. Higher prevalence and levels of Salmonella were previously observed in floater pistachios, but contributing factors are unclear. To examine the behavior of pathogens on hulled pistachios during simulated drying delays, floater and sinker pistachios collected from commercial processors were inoculated at 1 or 3 log CFU/g with cocktails of Salmonella and in some cases Escherichia coli O157:H7 or Listeria monocytogenes and incubated for up to 30 h at 37°C and 90% relative humidity. Populations were measured by plating onto tryptic soy agar and appropriate selective agars. In most cases, no significant growth (P > 0.05) of Salmonella was observed in the first 3 h after inoculation in hulled floaters and sinkers. Growth of Salmonella was greater on floater pistachios than on corresponding sinkers and on floater pistachios with ≥25% hull adhering to the shell surface than on corresponding floaters with <25% adhering hull. Maximum Salmonella populations (2 to 7 log CFU/g) were ∼2-log higher on floaters than on corresponding sinkers. The growth of E. coliO157:H7 and Salmonella on hulled pistachios was similar, but a longer lag time (approximately 11 h) and significantly lower maximum populations (4 versus 5 to 6 log CFU/g; P < 0.05) were predicted for L. monocytogenes. Significant growth of pathogens on hulled pistachios is possible when delays between hulling and drying are longer than 3 h, and pathogen growth is enhanced in the presence of adhering hull material.

HIGHLIGHTS
  • Foodborne pathogens multiplied on undried inshell pistachios.

  • Pathogen growth was greater when hull material was present.

  • Drying delays of >3 h led to significant increases in pathogen populations.

  • Managing drying delays will reduce the risk for growth of foodborne pathogens.

Research – Efficacy of Acetic Acid or Chitosan for Reducing the Prevalence of Salmonella- and Escherichia coli O157:H7–Contaminated Leafy Green Plants in Field Systems

Journal of Food Protection

ABSTRACT

Outbreaks associated with fresh-cut leafy greens continue to occur despite efforts to implement horticultural practices that minimize introduction of enteric pathogens to the crop. The experimental trials in this study were designed to examine the efficacy of an acetic acid (AA)- and chitosan-based spray treatment, applied 1 day prior to harvest, for reducing the prevalence of Escherichia coli O157:H7 (O157) and Salmonella in field-grown leafy greens contaminated at levels detectable only through enrichment culture. Responses to the treatment solution were variable and depended on the type of leafy green (leafy lettuce, spinach, or cabbage), cultivar, pathogen, and AA concentration (0.3 to 0.7%). No significant differences in E. coli O157 prevalence were found for untreated and treated cabbage heads and spinach plants (P > 0.05). In contrast, treatment significantly affected Salmonella on ‘Bravo F1’ green cabbage and ‘7-Green’ spinach (P < 0.05), with odds ratios of 2.2 and 3.3 for finding the pathogen on untreated versus treated greens, respectively. Salmonella was also 7.1 times more likely to be found on an untreated lettuce plant than on a lettuce plant sprayed with a 0.7% AA treatment solution (95% confidence interval [CI], 4.1 to 12.2; P < 0.0001). In studies addressing the efficacy of chitosan (0.1 or 0.3%), this chemical failed to reduce the prevalence of either pathogen on lettuce (P > 0.05). Similarly, spraying with 0.3% AA did not affect the prevalence of Salmonella on lettuce plants (P > 0.05); however, treatment solutions with 0.4% AA reduced the likelihood of detecting Salmonella in treated versus untreated plants by 6.6 times (95% CI, 2.1 to 20.9; P = 0.0007). After the lettuce was harvested and hand washed, consumers failed to distinguish either visually or organoleptically between untreated lettuce and lettuce sprayed with an acetic acid solution (P > 0.05). These results indicate that acetic acid could be used to reduce the microbiological risk of preharvest leafy greens.

Research – Efficacy of Acetic Acid or Chitosan for Reducing the Prevalence of Salmonella- and Escherichia coli O157:H7–Contaminated Leafy Green Plants in Field Systems

Journal of Food Protection

Outbreaks associated with fresh-cut leafy greens continue to occur despite efforts to implement horticultural practices that minimize introduction of enteric pathogens to the crop. The experimental trials in this study were designed to examine the efficacy of an acetic acid (AA)- and chitosan-based spray treatment, applied 1 day prior to harvest, for reducing the prevalence of Escherichia coli O157:H7 (O157) and Salmonella in field-grown leafy greens contaminated at levels detectable only through enrichment culture. Responses to the treatment solution were variable and depended on the type of leafy green (leafy lettuce, spinach, or cabbage), cultivar, pathogen, and AA concentration (0.3 to 0.7%). No significant differences in E. coli O157 prevalence were found for untreated and treated cabbage heads and spinach plants (P > 0.05). In contrast, treatment significantly affected Salmonella on ‘Bravo F1’ green cabbage and ‘7-Green’ spinach (P < 0.05), with odds ratios of 2.2 and 3.3 for finding the pathogen on untreated versus treated greens, respectively. Salmonella was also 7.1 times more likely to be found on an untreated lettuce plant than on a lettuce plant sprayed with a 0.7% AA treatment solution (95% confidence interval [CI], 4.1 to 12.2; P < 0.0001). In studies addressing the efficacy of chitosan (0.1 or 0.3%), this chemical failed to reduce the prevalence of either pathogen on lettuce (P > 0.05). Similarly, spraying with 0.3% AA did not affect the prevalence of Salmonella on lettuce plants (P > 0.05); however, treatment solutions with 0.4% AA reduced the likelihood of detecting Salmonella in treated versus untreated plants by 6.6 times (95% CI, 2.1 to 20.9; P = 0.0007). After the lettuce was harvested and hand washed, consumers failed to distinguish either visually or organoleptically between untreated lettuce and lettuce sprayed with an acetic acid solution (P > 0.05). These results indicate that acetic acid could be used to reduce the microbiological risk of preharvest leafy greens.

Research – Effects of Package Atmosphere and Storage Conditions on Minimizing Risk of Escherichia coli O157:H7 in Packaged Fresh Baby Spinach

Journal of Food Protection

ABSTRACT

Packaged fresh spinach has been associated with outbreaks of illness caused by Escherichia coli O157:H7. The purpose of this study was to assess the behavior of E. coli O157:H7 in packaged baby spinach in response to storage conditions of temperature and package atmosphere and including effects of inoculation level, spinach leaf damage (cut leaves), internalized or leaf surface contamination, exposure to hypochlorite sanitizer, and package size. Behavior of E. coli O157:H7 inoculated at 2 and 4 log CFU/g on spinach packaged in polymer bags composed of a two-layer laminate (polypropylene and polyethylene) and stored under atmospheres of 20% O2–3% CO2 and 0% O2–15% CO2 (aerobic and anaerobic, respectively) was assessed at 5, 7, 12, and 15°C for up to 14 days. Growth kinetics were calculated using DMFit software. Temperature decreases progressively diminished growth or survival of the pathogen, and an aerobic package atmosphere resulted in longer lag times (4 to 6 days) and lower population levels (0.2 to 1.4 log CFU/g) compared with the anaerobic atmosphere at 15°C. Internalized contamination, leaf cuts, or exposure to 100 ppm of hypochlorite did not result in changes in pathogen behavior compared with controls; however, a growth minimization trend consisting of longer lag times and lower population levels was repeatedly observed in the aerobic compared with the anaerobic package atmospheres. In contrast, growth of indigenous mesophiles and Enterobacteriaceae was unaffected by package atmosphere. Spinach stored at 5 to 7°C in two sizes (5 and 16 oz) of polyethylene terephthalate clamshell packages with ambient air atmospheres was more likely to progress to lower-oxygen conditions in 16-oz compared with 5-oz packages after 7 days of storage (P < 0.05). Practices to maintain aerobic conditions within the package, as well as storage of the package at low temperature, are ways to limit growth of E. coli O157:H7 in packaged spinach.

HIGHLIGHTS
  • Cold aerobic conditions limited survival of E. coli O157:H7 in packaged spinach.

  • Low-oxygen atmosphere increased pathogen risk in temperature-abused packages.

  • Internalization, leaf cuts, and hypochlorite stress did not increase pathogen risk.

  • Large spinach packages trended toward lower-oxygen conditions more than small packages.

  • Maintaining cold aerobic conditions can limit pathogen risk in packaged spinach.

Research – Comparison of Antimicrobial Treatments Applied via Conventional or Handheld Electrostatic Spray To Reduce Shiga Toxin–Producing Escherichia coli on Chilled Beef Outside Rounds

Journal of Food Protection

The purpose of this study was to compare the efficacy of different antimicrobial interventions applied via either conventional spray (CS) or handheld electrostatic spray (ESS) to reduce Shiga toxin–producing Escherichia coli (STEC) on fresh beef surfaces. Hot-boned outside rounds (ORs) were inoculated within 1 h after harvest with a cocktail of eight isolates consisting of 8 O157 and non-O157 serogroups of STEC (STEC8). ORs were hung on sterile meat hooks at 4°C for 36 h to simulate a contaminated full carcass side in the chiller. ORs were then treated with lactic acid (LA; 4.5%, w/v), 3.0% lauric arginate ester (LAE), 0.8% cetylpyridinium chloride, 200 mg/L peracetic acid, 3 mg/L chlorine dioxide, 5 mg/L ClO2, or tap water by using CS or ESS. Temperatures of LA and peracetic acid were set at 55 and 42°C before spraying, whereas all other solutions were applied at room temperature (25°C). Pretreatment and posttreatment STEC8-inoculated beef tissue samples were aseptically collected to evaluate the efficacy of interventions by application method (CS or ESS). LA applied with CS achieved the greatest reduction in STEC8 numbers (3.3 log CFU/cm2) compared with all other treatments: 0.2 log CFU/cm2 (tap water) to 2.3 log CFU/cm2 (LAE). Only for LA did a significant difference arise in mean STEC8 reductions between CS and ESS applications (3.2 versus 1.7 log CFU/cm2, respectively). Among the treatments applied with ESS, LAE produced the greatest reduction of STEC8. Antimicrobial interventions applied via conventional wand or cabinet-applied technologies can reduce the O157 and non-O157 STEC on fresh beef carcass surfaces, reducing transmission to beef consumers.

HIGHLIGHTS
  • We found no advantage in the use of electrostatic spray to reduce STEC8 on cold beef.

  • Greatest reductions in STEC8 were achieved by lactic acid with conventional spray.

  • Lauric arginate ester was the second best antimicrobial agent at reducing STEC8.

  • Lactic acid reduced pH on the beef surface significantly.

  • There was no effect of antimicrobial solution on temperature increase on beef outside rounds.