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.     

Use of mustard flour to inactivate Escherichia coli O157:H7 in ground beef under nitrogen flushed packaging

This study was undertaken to determine whether the glucosinolates naturally present in non-deheated mustard flour could serve as a source of allyl and other isothiocyanates in sufficient quantity to kill Escherichia coli O157:H7 inoculated in ground beef at three different levels, during refrigerated storage of the meat under nitrogen. Mustard flour was mixed at 5%, 10% or 20% (w/w) with freshly ground beef, then the beef was inoculated with a cocktail of five strains of E. coli O157:H7 at either 3, 6 or < or =1.6 log10 cfu/g. The ground beef was formed into 100 g patties and each was placed in a bag of Nylon/EVOH/PE, which was back-flushed with 100% N2, heat-sealed and stored at 4 degrees C for < or =21 days. During storage, the allyl isothiocyanate (AIT) levels in package headspaces were determined by gas liquid chromatography. By 21 days, the levels present in treatments were not significantly different. After 21 days storage, there were 0.5, 3 and 5.4 log10 decreases in numbers of E. coli O157:H7 from the initial levels of 6 log10 cfu/g in meat containing 5%, 10% and 20% mustard flour, respectively. When inoculated at 3 log10 cfu/g, E. coli O157:H7 was reduced to undetectable levels after 18, 12 and 3 days with 5%, 10% and 20% mustard flour, respectively. When immunomagnetic separation (IMS) was used for E. coli recovery following its inoculation at < or =1.6 log10 cfu/g, 5% mustard did not completely eliminate the pathogen from ground beef stored for 6 days. The natural microflora of the ground beef which developed in vacuum packages was unaffected by the addition of 5% mustard flour but some inhibition was found at higher concentrations. Sensory evaluation of the cooked ground beef showed that there were no significant differences in the acceptability of meat treated with 5 or 10% mustard flour. However, panelists could distinguish untreated controls from mustard treatments, but considered the mustard-treated meat to be acceptable. These results showed that it is possible to use mustard flour at levels of >5-10% to eliminate E. coli O157:H7 from fresh ground beef.     

Survival of Escherichia coli O157:H7 and Salmonella enterica serovars Typhimurium in iceberg lettuce and the antimicrobial effect of rice vinegar against E. coli O157:H7

The microbiological safety of fresh produce is a significant concern of consumers and industry. After applying at an inoculated level (about 10(6) CFUg(-1)) of E. coli O157:H7 and Salmonella enterica serovars Typhimurium on shredded iceberg lettuce and water samples individually, they were stored at 4 degrees C for 14 days and 22 degrees C for 7 days to monitor the growth and survival of pathogens. The results showed that at the end of 4 degrees C storage, populations of two pathogens in lettuce and water decreased approximately 1 log CFUg(-1). However, microbial levels on shredded lettuce increased 3 logs within 3 days at 22 degrees C. Vinegar (acetic acid) had been used to reduce populations of foodborne pathogens in foods; hence, the antimicrobial effect of rice vinegar on the survival of E. coli O157:H7 in inoculated lettuce (10(4) and 10(7) CFUg(-1)) is examined in this study. Results were observed that the treatment of inoculated lettuce (10(7) CFUg(-1)) with commercial vinegar containing 5% acetic acid (pH 3.0) for 5 min would reduce 3 logs population at 25 degrees C. Less than a 1-log decrease in bacterial numbers was recovered during 5 min exposure to 0.5% (pH 3.26) acetic acid.     

Thermal inactivation of Escherichia coli O157:H7 in beef treated with marination and tenderization ingredients

Internalization of Escherichia coli O157:H7 in nonintact beef products during mechanical tenderization or during injection of marination and tenderization ingredients is of concern if such products are undercooked. This study tested organic acids (0.2% citric acid and 0.3% acetic acid), potassium and calcium salts (1.8% potassium lactate, 0.63% calcium lactate, 0.86% calcium ascorbate, and 0.23% calcium chloride), and sodium chloride (2.5%) for their influence on thermal destruction of E. coli O157:H7 in ground beef serving as a model system. Ground beef batches (700 g; 5% fat) were mixed with equal volumes (22 ml) of each treatment solution or distilled water and portions (30 g) of treated ground beef were extruded in test tubes (2.5 by 10 cm). A five-strain mixture of E. coli O157:H7 (0.3 ml; 7 log CFU/g) was introduced at the center of the sample with a pipette. After overnight storage (4 degrees C), simulating product marination, samples were heated to 60 or 65 degrees C internal temperature, simulating rare and medium rare doneness of beef, in a circulating water bath. At 65 degrees C, treatments with citric and acetic acid showed greater (P < 0.05) reduction (4 to 5 log CFU/g) of E. coli O157:H7 than all the other ingredients and the control (3 to 4 log CFU/g). Sodium chloride reduced weight losses (16 to 18% compared with 20 to 27% by citric or acetic acid) and resulted in a 4-log reduction in counts during cooking to 65 degrees C. Ingredients such as citric or acetic acid may improve thermal inactivation of E. coli O157:H7 internalized in nonintact beef products, while sodium chloride may reduce cooking losses in such products.     

Influence of extended acid stressing in fresh beef decontamination runoff fluids on sanitizer resistance of acid-adapted Escherichia coli O157:H7 in biofilms

This study evaluated resistance to sanitizing solutions of Escherichia coli O157:H7 cells forming biofilms on stainless steel coupons exposed to inoculated meat decontamination runoff fluids (washings). A previously acid-adapted culture of a rifampicin-resistant derivative of E. coli O157:H7 strain ATCC 43895 was inoculated in unsterilized or sterilized combined hot-water (85 degrees C) and cold-water (10 degrees C) (50/50 [vol/vol]) composite water (W) washings (pH 6.29 to 6.47) and in W washings mixed with 2% acetic acid (pH 4.60 to 4.71) or in 2% lactic acid W washings (pH 4.33 to 4.48) at a ratio of 1/99 (vol/vol). Stainless steel coupons (2 by 5 by 0.08 cm) were submerged in the inoculated washings and stored for up to 14 days at 15 degrees C. Survival of E. coli O157:H7 was determined after exposure (0 to 60 s for cells in suspension and 0 to 300 s for attached cells) to two commercial sanitizers (150 ppm peroxyacetic acid and 200 ppm quaternary ammonium compound) at 2, 7, and 14 days. E. coli O157:H7 attached more rapidly to coupons submerged in washings containing the natural flora than to those without. The attached cells were more resistant to the effects of the sanitizers than were the cells in suspension, and survival was highest in the presence of the natural flora. Attached cells in the presence of dilute acid washings were more sensitive to subsequent sanitizer treatments than were cells generated in the presence of W washings. Under the conditions of this study, cells of E. coli O157:H7 in W washings were more sensitive to acidic (peroxyacetic acid) than to alkaline (quaternary ammonium) sanitizers during storage. These results suggest that meat processing plants that apply no decontamination or that use only water washings of meat should consider using acidic sanitizers to enhance biofilm removal. Plants that apply both water and acidic washings may create a sublethal acid-stressing environment in the runoff fluids, sensitizing biofilm cells to subsequent sanitizing treatments.     

Growth and survival of Escherichia coli O157:H7 and Listeria monocytogenes in egg products held at different temperatures

Growth and survival of Escherichia coli O157:H7 and Listeria monocytogenes in steamed eggs and scrambled eggs held at different temperatures (5, 18, 22, 37, 55, and 60 degrees C) were investigated in the present study. Among the holding temperatures tested, both pathogens multiplied best at 37 degrees C followed by 22, 18, and 5 degrees C. In general, E. coli O157:H7 grew better in the egg products than L. monocytogenes did at all the storage temperatures tested except at 5 degrees C. E. coli O157:H7 did not grow in steamed eggs and scrambled eggs held at 5 degrees C. L. monocytogenes showed a slight population increase of approximately 0.6 to 0.9 log CFU/g in these egg products at the end of the 36-h storage period at 5 degrees C. The population of both pathogens detected in the egg products was affected by the initial population, holding temperature, and length of the holding period. It was also noted that L. monocytogenes was more susceptible than E. coli O157:H7 in steamed eggs held at 60 degrees C. After holding at 60 degrees C for 1 h, no detectable viable cells of L. monocytogenes with a population reduction of 5.4 log CFU/g was observed in steamed eggs, whereas a lower population reduction of only approximately 0.5 log CFU/ml was noted for E. coli O157:H7.     

Acid tolerance of acid-adapted and nonadapted Escherichia coli O157:H7 following habituation (10 degrees C) in fresh beef decontamination runoff fluids of different pH values

This study evaluated survival of Escherichia coli O157:H7 strain ATCC 43895 during exposure to pH 3.5 following its habituation for 2 or 7 days at 10 degrees in fresh beef decontamination waste runoff fluid mixtures (washings) containing 0, 0.02, or 0.2% of lactic or acetic acids. Meat washings and sterile water (control) were initially inoculated with approximately 5 log CFU/ml of acid- and nonadapted E. coli O157:H7 cells cultured (30 degrees C, 24 h) in broth with and without 1% glucose, respectively. After 2 days, E. coli O157:H7 survivors from acetate washings (pH 3.7 to 4.7) survived at pH 3.5 better than E. coli O157:H7 survivors from lactate washings (pH 3.1 to 4.6), especially when the original inoculum was acid adapted. Also, although E. coli O157:H7 habituated in sterile water for 2 days survived well at pH 3.5, the corresponding survivors from nonacid water meat washings (pH 6.8) were rapidly killed at pH 3.5, irrespective of acid adaptation. After 7 days, E. coli O157:H7 survivors from acetate washings (pH 3.6 to 4.7) continued to resist pH 3.5, whereas those from lactate washings died off. This loss of acid tolerance by E. coli O157:H7 was due to either its low survival in 0.2% lactate washings (pH 3.1) or its acid sensitization in 0.02% lactate washings, in which a Pseudomonas-like natural flora showed extensive growth (> 8 log CFU/ml) and the pH increased to 6.5 to 6.6. Acid-adapted E. coli O157:H7 populations habituated in water washings (pH 7.1 to 7.3) for 7 days continued to be acid sensitive, whereas nonadapted populations increased their acid tolerance, a response merely correlated with their slight (< 1 log) growth at 10 degrees C. These results indicate that the expression of high acid tolerance by acid-adapted E. coli O157:H7 can be maintained or enhanced in acid-diluted meat decontamination waste runoff fluids of pH levels that could permit long-term survival at 10 degrees C. Previous acid adaptation, however, could reduce the growth potential of E. coli O157:H7 at 10 degrees C in nonacid waste fluids of high pH and enriched in natural flora. These conditions might further induce an acid sensitization to stationary E. coli O157:H7 cells.     

Effect of acid adaptation on survival of Escherichia coli O157:H7 in meat decontamination washing fluids and potential effects of organic acid interventions on the microbial ecology of the meat plant environment.

The acid tolerance of Escherichia coli O157:H7 may be pH inducible. Correspondingly, organic acid meat decontamination washing fluids may enhance the establishment of acid-adapted E. coli O157:H7 strains in packing plants, especially in mixtures with water washings from meat that may be of sublethal pH. Acid-adapted and nonadapted cultures of a rifampin-resistant derivative of the acid-resistant E. coli O157:H7 strain ATCC 43895 were tested to evaluate their survival in meat-washing fluids over a wide pH range. The cultures were exposed (10(5) CFU/ml) to acidic (2% lactic acid. 2% acetic acid, or a mixture of the two with water washings at ratios of 1/1, 1/9, or 1/99 [vol/vol]) or nonacid (water) meat washings for up to 14 days at 4 or 10 degrees C storage. E. coli O157:H7 survived in water washings, but the low storage temperatures and predominant natural microbiota synergistically inhibited its growth. Compared with acid-adapted populations, nonadapted populations displayed greater potential for survival and a tendency to initiate growth in water meat washings at 10 degrees C. The pathogen survived in most of the acid washings throughout storage (14 days), sometimes with minimal population reductions. Overall. nonadapted populations declined faster than acid-adapted populations, while the declines increased as the acid concentration and temperature of storage increased and were more dramatic in lactate, compared to acetate, washings. Acid-containing washings were selective for growth of lactic acid bacteria and yeasts. indicating that organic acid treatments may alter the microbial ecology of meat plant environments and potentially that of the meat. These results should be considered when selecting decontamination technologies for meat.     

Determination of 5-log reduction times for food pathogens in acidified cucumbers during storage at 10 and 25 degrees C

Outbreaks of acid-resistant foodborne pathogens in acid foods with pH values below 4.0, including apple cider and orange juice, have raised concerns about the safety of acidified vegetable products. For acidified vegetable products with pH values between 3.3 and 4.6, previous research has demonstrated that thermal treatments are needed to achieve a 5-log reduction in the numbers of Escherichia coli O157:H7, Listeria monocytogenes, or Salmonella enterica. For some acidified vegetable products with a pH of 3.3 or below, heat processing can result in unacceptable product quality. The purpose of this study was to determine the holding times needed to achieve a 5-log reduction in E. coli O157:H7, L. monocytogenes, and S. enterica strains in acidified vegetable products with acetic acid as the primary acidulant, a pH of 3.3 or below, and a minimum equilibrated temperature of 10 degrees C. We found E. coli O157:H7 to be the most acid-resistant microorganism for the conditions tested, with a predicted time to achieve a 5-log reduction in cell numbers at 10 degrees C of 5.7 days, compared with 2.1 days (51 h) for Salmonella or 0.5 days (11.2 h) for Listeria. At 25 degrees C, the E. coli O157:H7 population achieved a 5-log reduction in 1.4 days (34.3 h).     

Protective effect of exopolysaccharide colanic acid of Escherichia coli O157:H7 to osmotic and oxidative stress

Many strains of Escherichia coli O157:H7 produce, under stress, an exopolysaccharide (EPS) comprised of colanic acid (CA) and form mucoid colonies on minimal glucose agar (MGA) at ambient temperature. Previous research conducted in our laboratory involving a CA-proficient (W6-13) and a CA-deficient (M4020; wcaD::Ekan(r)) strain of E. coli O157:H7 revealed that CA conferred acid and heat tolerance to E. coli O157:H7. Cells covered with CA were more persistent during acid (pH 4.5, 5.5, and 6.5) and heat (55 and 60 degrees C) treatment. The goal of this research was to study the effect of CA on the fate of E. coli O157:H7 under osmotic and oxidative stress. Cells of W6-13 and M4020 were exposed to various concentrations of NaCl (0.5, 1.5, and 2.5 M) and H2O2 (0, 10, and 20 mM) in minimal glucose broth (MGB) at 22 degrees C. Viable counts of E. coli O157:H7 were determined within 48 h of the osmotic stress and 3 h of the oxidative stress. The results suggest that cells of E. coli O157:H7 deficient in CA production are more susceptible than its wild-type parent to NaCl ( P< 0.05) and H2O2 (P< or = 0.05). This indicates that CA plays a role in protecting E. coli O157:H7 from osmotic and oxidative stress.     

Application of reuterin produced by Lactobacillus reuteri 12002 for meat decontamination and preservation

Lactobacillus reuteri strain 12002 was used for reuterin production in the two-step fermentation process. A batch culture fermentation was used to produce a maximum biomass of L. reuteri. Then cells were harvested, resuspended in a glycerol-water solution, and anaerobically incubated to produce reuterin. The lyophilized supernatants (approximately 4000 activity units (AU) of reuterin per ml) were diluted in distilled water for decontamination and preservation trials. The MIC values of reuterin for Escherichia coli O157:H7 and Listeria monocytogenes were 4 and 8 AU/ml, respectively. In meat decontamination experiments, the surface of cooked pork was inoculated with either L. monocytogenes or E. coli O157:H7 at a level of approximately log10 5 CFU/cm2, incubated for 30 min at 7 degrees C, and decontaminated by exposure to reuterin (500 AU/ml). The bactericidal effect of reuterin was analyzed 15 s and 24 h after exposure at 7 degrees C. After 15 s of exposure to reuterin, viable numbers decreased by 0.45 and 0.3 log10 CFU/cm2 for E. coli O157:H7 and L. monocytogenes, respectively. After 24 h the numbers decreased by 2.7 log10 CFU/cm2 for E. coli O157:H7 and by 0.63 log10 CFU/cm2 for L. monocytogenes. In the same experiment, the combined effect of reuterin and lactic acid was also investigated. Adding lactic acid (5%, vol/vol) to reuterin significantly enhanced (P < or = 0.05) the efficacy of reuterin. No additional effect (P < or = 0.05) was found when ethanol (40%) was added to the mixture of reuterin and lactic acid. To evaluate the preservative effect of reuterin during meat storage, reuterin was added to raw ground pork contaminated with E. coli O157:H7 or L. monocytogenes. Reuterin at a concentration of 100 AU/g resulted in a 5.0-log10 reduction of the viability of E. coli O157:H7 after 1 day of storage at 7 degrees C. Reuterin at a concentration of 250 AU/g reduced the number of the viable cells of L. monocytogenes by log10 3.0 cycles after 1 week of storage at 7 degrees C.     

Chlorine inactivation of Escherichia coli O157:H7 in water

Six human isolates of Escherichia coli O157:H7 and E. coli (ATCC 11229) were used to determine the concentrations of free chlorine and exposure times required for inactivation. Free chlorine concentrations of 0.25, 0.5, 1.0, and 2.0 ppm at 23 degrees C were evaluated, with sampling times at 0, 0.5, 1.0, and 2.0 min. Results revealed that five of six E. coli O157:H7 isolates and the E. coli control strain were highly susceptible to chlorine, with >7 log10 CFU/ml reduction of each of these strains by 0.25 ppm free chlorine within 1 min. However, comparatively, one of the seven strains was unusually tolerant to chlorine at 23 degrees C for 1 min, with a 4-, 5.5-, 5.8-, and >5.8-log CFU/ml reduction at free chlorine concentrations (ppm) of 0.25, 0.5, 1.0, and 2.0. respectively. Based on these studies most isolates of E. coli O157:H7 have no unusual tolerance to chlorine; however, one strain was exceptional in being recovered after 1-min of exposure of 10(7) CFU/ml to 2.0 ppm of free chlorine. This isolate may be a useful reference strain for future studies on chlorine tolerance of E. coli O157:H7.     

Effect of stress induced by suboptimal growth factors on survival of Escherichia coli O157:H7.

This study investigated the growth and survival of E. coli O157:H7 exposed to a combination of suboptimal factors (22 degrees C, 7 degrees C, -18 degrees C/0.5% NaCl, 5.0% NaCl/pH 7.0, pH 5.4, pH 4.5/addition of lactic acid) in a simulation medium for red meat (beef gravy). Prolonged survival was noted as the imposed stress was more severe, and as multiple growth factors became suboptimal. At a defined temperature (7 degrees C or -18 degrees C), survival was prolonged at the more acid, more suboptimal pH (pH 4.5 > pH 5.4 > pH 7.0) while at a defined pH (pH 4.5), better survival was observed at 7 degrees C than at 22 degrees C. This suggests that application of the hurdle concept for preservation of food may inhibit outgrowth but induce prolonged survival of E. coli O157:H7 in minimal processed foods. At both 22 degrees C and 7 degrees C, the addition of lactic acid instead of HCl to reduce pH (to pH 4.5) resulted in a more rapid decrease of E. coli O157:H7. High survival was observed in beef gravy, pH 5.4 at -18 degrees C (simulation of frozen meat)-reduction of log 3.0 to log 1.9 after 43 days--and in beef gravy, pH 4.5 and 5% NaCl at 7 degrees C (simulation of a fermented dried meat product kept in refrigeration)--less than 1 log reduction in 43 days. In these circumstances, however, a high degree of sublethal damage of the bacterial cells was noted. The degree of sublethal damage can be estimated from the difference in recovery of the pathogen on the non-selective TSA medium and the selective SMAC medium.     

Interventions for the reduction of Salmonella Typhimurium DT 104 and non-O157:H7 enterohemorrhagic Escherichia coli on beef surfaces

A study was conducted to determine if slaughter interventions currently used by the meat industry are effective against Salmonella Typhimurium definitive type 104 (DT 104) and two non-O157:H7 enterohemorrhagic Escherichia coli (EHEC). Three separate experiments were conducted by inoculating prerigor beef surfaces with a bovine fecal slurry containing Salmonella Typhimurium and Salmonella Typhimurium DT 104 (experiment 1), E. coli O157:H7 and E. coli O111:H8 (experiment 2), or E. coli O157:H7 and E. coli O26:H11 (experiment 3) and spray washing with water, hot water (72 degrees C), 2% acetic acid, 2% lactic acid, or 10% trisodium phosphate (15 s, 125 +/- 5 psi, 35 +/- 2 degrees C). Remaining bacterial populations were determined immediately after treatments (day 0), after 2 days of aerobic storage at 4 degrees C, and after 7, 21, and 35 days of vacuum-packaged storage at 4 degrees C. In addition to enumeration, confirmation of pathogen serotypes was performed for all treatments on all days. Of the interventions investigated, spray treatments with trisodium phosphate were the most effective, resulting in pathogen reductions of >3 log10 CFU/cm2, followed by 2% lactic acid and 2% acetic acid (>2 log10 CFU/cm2). Results also indicated that interventions used to reduce Salmonella Typhimurium on beef surfaces were equally effective against Salmonella Typhimurium DT 104 immediately after treatment and again after long-term, refrigerated, vacuum-packaged storage. Similarly, E. coli O111:H8 and E. coli O26:H11 associated with beef surfaces were reduced by the interventions to approximately the same extent as E. coli O157:H7 immediately after treatment and again after long-term, refrigerated, vacuum-packaged storage. It was also demonstrated that phenotypic characterization may not be sufficient to identify EHECs and that the organisms should be further confirmed with antibody- or genetic-based techniques. Based on these findings, interventions used by the meat industry to reduce Salmonella spp. and E. coli O157:H7 appear to be effective against DT 104 and other EHEC.     

Effects of water source, dilution, storage, and bacterial and fecal loads on the efficacy of electrolyzed oxidizing water for the control of Escherichia coli O157:H7

To evaluate the potential of using electrolyzed oxidizing (EO) water for controlling Escherichia coli O157:H7 in water for livestock, the effects of water source, electrolyte concentration, dilution, storage conditions, and bacterial or fecal load on the oxidative reduction potential (ORP) and bactericidal activity of EO water were investigated. Anode and combined (7:3 anode:cathode, vol/vol) EO waters reduced the pH and increased the ORP of deionized water, whereas cathode EO water increased pH and lowered ORP. Minimum concentrations (vol/vol) of anode and combined EO waters required to kill 10(4) CFU/ml planktonic suspensions of E. coli O157:H7 strain H4420 were 0.5 and 2.0%, respectively. Cathode EO water did not inhibit H4420 at concentrations up to 16% (vol/vol). Higher concentrations of anode or combined EO water were required to elevate the ORP of irrigation or chlorinated tap water compared with that of deionized water. Addition of feces to EO water products (0.5% anode or 2.0% combined, vol/vol) significantly reduced (P < 0.001) their ORP values to < 700 mV in all water types. A relationship between ORP and bactericidal activity of EO water was observed. The dilute EO waters retained the capacity to eliminate a 10(4) CFU/ml inoculation of E. coli O157:H7 H4420 for at least 70 h regardless of exposure to UV light or storage temperature (4 versus 24 degrees C). At 95 h and beyond, UV exposure reduced ORP, significantly more so (P < 0.05) in open than in closed containers. Bactericidal activity of EO products (anode or combined) was lost in samples in which ORP value had fallen to < or = 848 mV. When stored in the dark, the diluted EO waters retained an ORP of > 848 mV and bactericidal efficacy for at least 125 h; with refrigeration (4 degrees C), these conditions were retained for at least 180 h. Results suggest that EO water may be an effective means by which to control E. coli O157:H7 in livestock water with low organic matter content.     

Survival and growth characteristics of Escherichia coli O157:H7 in pasteurized and unpasteurized Cheddar cheese whey

The objective of this study was to determine the survival and growth characteristics of Escherichia coli O157:H7 in whey. A five-strain mixture of E. coli O157:H7 was inoculated into 100 ml of fresh, pasteurized or unpasteurized Cheddar cheese whey (pH 5.5) at 10(5) or 10(2) CFU/ml, and stored at 4, 10 or 15 degrees C. The population of E. coli O157:H7 (on Sorbitol MacConkey agar supplemented with 0.1% 4-methylumbelliferyl-beta-D-glucuronide) and lactic acid bacteria (on All Purpose Tween agar) were determined on days 0, 1, 4, 7, 14, 21 and 28. At all storage temperatures, survival of E. coli O157:H7 was significantly higher (P<0.01) in the pasteurized whey compared to that in the unpasteurized samples. At 10 and 15 degrees C, E. coli O157:H7 in pasteurized whey significantly (P<0.05) increased during the first week of storage, followed by a decrease thereafter. However at the same temperatures, E. coli O157:H7 exhibited a steady decline in the unpasteurized samples from day 0. At 4 degrees C, E. coli O157:H7 did not grow in pasteurized and unpasteurized whey; however, the pathogen persisted longer in pasteurized samples. At all the three storage temperatures, E. coli O157:H7 survived up to day 21 in the pasteurized and unpasteurized whey. The initial load of lactic acid bacteria in the unpasteurized whey samples was approximately 7.0 log10 CFU/ml and, by day 28, greater than 3.0 log10 CFU/ml of lactic acid bacteria survived in unpasteurized whey at all temperatures, with the highest counts recovered at 4 degrees C. Results indicate the potential risk of persistence of E. coli O157:H7 in whey in the event of contamination with this pathogen.     

Acid stress, starvation, and cold stress affect poststress behavior of Escherichia coli O157:H7 and nonpathogenic Escherichia coli.

The effects of acid shock, acid adaptation, starvation, and cold stress of Escherichia coli O157:H7 (ATCC 43895), an rpoS mutant (FRIK 816-3), and nonpathogenic E. coli (ATCC 25922) on poststress heat resistance and freeze-thaw resistance were investigated. Following stress, heat tolerance at 56 degrees C and freeze-thaw resistance at -20 to 21 degrees C were determined. Heat and freeze-thaw resistance of E. coli O157:H7 and nonpathogenic E. coli was enhanced after acid adaptation and starvation. Following cold stress, heat resistance of E. coli O157:H7 and nonpathogenic E. coli was decreased, while freeze-thaw resistance was increased. Heat and freeze-thaw resistance of the rpoS mutant was enhanced only after acid adaptation. Increased or decreased tolerance of acid-adapted, starved, or cold-stressed E. coli O157:H7 cells to heat or freeze-thaw processes should be considered when processing minimally processed or extended shelf-life foods.     

Addition of fumaric acid and sodium benzoate as an alternative method to achieve a 5-log reduction of Escherichia coli O157:H7 populations in apple cider

A study was conducted to develop a preservative treatment capable of the Food and Drug Administration-mandated 5-log reduction of Escherichia coli O157:H7 populations in apple cider. Unpreserved apple cider was treated with generally recognized as safe acidulants and preservatives before inoculation with E. coli O157:H7 in test tubes and subjected to mild heat treatments (25, 35, and 45 degrees C) followed by refrigerated storage (4 degrees C). Fumaric acid had significant (P < 0.05) bactericidal effect when added to cider at 0.10% (wt/vol) and adjusted to pH 3.3, but citric and malic acid had no effect. Strong linear correlation (R2 = 0.96) between increasing undissociated fumaric acid concentrations and increasing log reductions of E. coli O157:H7 in apple cider indicated the undissociated acid to be the bactericidal form. The treatment that achieved the 5-log reduction in three commercial ciders was the addition of fumaric acid (0.15%, wt/vol) and sodium benzoate (0.05%, wt/vol) followed by holding at 25 degrees C for 6 h before 24 h of refrigeration at 4 degrees C. Subsequent experiments revealed that the same preservatives added to cider in flasks resulted in a more than 5-log reduction in less than 5 and 2 h when held at 25 and 35 degrees C, respectively. The treatment also significantly (P < 0.05) reduced total aerobic counts in commercial ciders to populations less than those of pasteurized and raw ciders from the same source (after 5 and 21 days of refrigerated storage at 4 degrees C, respectively). Sensory evaluation of the same ciders revealed that consumers found the preservative-treated cider to be acceptable.     

Essential oils reduce Escherichia coli O157:H7 and Salmonella on spinach leaves

The efficacy of cinnamaldehyde and Sporan for reducing Escherichia coli O157:H7 and Salmonella on spinach leaves was investigated. Spinach leaves were inoculated with a five-strain cocktail of Salmonella or E. coli O157:H7, air dried for ca. 30 min, and then immersed in a treatment solution containing 5 ppm of free chlorine, cinnamaldehyde, or Sporan (800 and 1,000 ppm) alone or in combination with 200 ppm of acetic acid (20%) for 1 min or with water (control). After spin drying, treated leaves were analyzed periodically during 14 days of storage at 4°C for Salmonella, E. coli O157:H7, total coliforms, mesophilic and psychrotrophic bacteria, and yeasts and molds. Treatment effects on color and texture of leaves also were determined. Sporan alone (1,000S), Sporan plus acetic acid (1,000SV), and cinnamaldehyde-Tween (800T) reduced E. coli O157:H7 by more than 3 log CFU/g (P < 0.05), and 1,000SV treatment reduced Salmonella by 2.5 log CFU/g on day 0. E. coli O157:H7 and Salmonella populations on treated spinach leaves declined during storage at 4°C. The 1,000SV treatment was superior to chlorine and other treatments for reducing E. coli O157:H7 during storage. Saprophytic microbiota on spinach leaves increased during storage at 4°C but remained lower on leaves treated with Sporan (800S) and Sporan plus acetic acid (1,000SV) than on control leaves. The color and texture of Sporan-treated leaves were not significantly different from those of the control leaves after 14 days. Sporan plus acetic acid (1,000SV) reduced E. coli O157:H7 and Salmonella on baby spinach leaves without adverse effects on leaf color and texture.     

Survival of Escherichia coli O157:H7 in buttermilk as affected by contamination point and storage temperature

The effects of contamination point (during fermentation versus postfermentation) and storage temperature (5 and 12 degrees C) were determined for survival of Escherichia coli O157:H7 in fermented buttermilk. E. coli O157:H7 was recovered from buttermilk inoculated during fermentation for 22 days and in buttermilk inoculated postfermentation for 32 days. For storage temperatures of 5 and 12 degrees C, D-values were lower for E. coli O157:H7 inoculated during fermentation (2.5, 2.2 days) than postfermentation (5.6, 4.8 days) (P < 0.05). Developed acidity in inoculated buttermilks was not different from controls (P > 0.05). The extended recovery of viable enterohemorrhagic E. coli O157:H7 from both processing scenarios indicates that the presence of E. coli O157:H7 in buttermilk is not limited to postprocessing contamination.