Effect of slightly acidic electrolyzed water for inactivating Escherichia coli O157:H7 and Staphylococcus aureus analyzed by transmission electron microscopy

The use of different available chlorine concentrations (ACCs) of slightly acidic electrolyzed water (SAEW; 0.5 to 30 mg/liter), different treatment times, and different temperatures for inactivating Escherichia coli O157:H7 and Staphylococcus aureus was evaluated. The morphology of both pathogens also was analyzed with transmission electron microscopy. A 3-min treatment with SAEW (pH 6.0 to 6.5) at ACCs of 2 mg/liter for E. coli O157:H7 and 8 mg/liter for S. aureus resulted in 100% inactivation of two cultures (7.92- to 8.75-log reduction) at 25°C. The bactericidal activity of SAEW was independent of the treatment time and temperature at a higher ACC (P > 0.05). E. coli O157:H7 was much more sensitive than S. aureus to SAEW. The morphological damage to E. coli O157:H7 cells by SAEW was significantly greater than that to S. aureus cells. At an ACC as high as 30 mg/liter, E. coli O157:H7 cells were damaged, but S. aureus cells retained their structure and no cell wall damage or shrinkage was observed. SAEW with a near neutral pH may be a promising disinfectant for inactivation of foodborne pathogens.     

Water, sodium chloride and acidified sodium chlorite effects on Escherichia coli O157:H7 and Staphylococcus aureus on beef briskets

Effectiveness of spray application of potable water wash (WW), 25% (w/v) sodium chloride (NaCl), and 0.1% (v/v) acidified sodium chlorite (ASC) was evaluated against Escherichia coli O157:H7 and Staphylococcus aureus inoculated onto beef briskets. The purpose was to identify antimicrobial treatments which may be applied to beef carcasses and more specifically in kosher meat facilities. Treatments were applied for 10-60 s at pressure of 419 kPa. Water wash, NaCl, and ASC significantly reduced E. coli O157:H7 as compared with the control, although, only ASC resulted in improved removal with increased exposure time. Water wash did not significantly reduce S. aureus counts throughout exposure and NaCl was only effective after 60 s of exposure, while ASC reduced counts throughout exposure. E. coli O157:H7 was twice as sensitive to WW and NaCl as S. aureus in terms of percent reduction in cell count.     

Survival of staphylococcus aureus and Escherichia coli as affected by ethanol and NaCl

Growth of three strains of Staphylococcus aureus and two strains of Escherichia coli on nutrient agar (NA) supplemented with ethanol and NaCl was investigated. S. aureus did not grow on NA containing > or =10% ethanol (wt/wt) combined with > or =0% NaCl (wt/wt), or 7.5% ethanol combined with 7.5% NaCl. Neither E. coli nor E. coli O157:H7 grew on NA containing > or =7.5% ethanol combined with > or =0% NaCl, 5% ethanol combined with > or =2.5% NaCl, or > or =5% NaCl combined with > or =0% ethanol. It is apparent that NaCl enhanced the inhibitory effect of ethanol on growth of S. aureus and E. coli When cells were suspended in nutrient broth containing 12.5, 20, or 40% ethanol combined with NaCl, viable cells decreased with an increase of ethanol concentration. Ethanol sensitivity among strains and between genera varied in a limited range. When the cells were exposed to 20% ethanol in combination with 5% NaCl, S. aureus and E. coli lost viability after 30 and 10 min, respectively. When treated with 40% ethanol combined with > or =0% NaCl, all test strains lost viability within 5 min.     

Difference between Escherichia coli O157:H7 and non-pathogenic E. coli: survival and growth in seasonings

We examined the survival and growth of Escherichia coli O157:H7 cells incubated with several seasonings, in comparison with those of non-pathogenic E. coli. The cells were incubated at 25 degrees C for 24 h with several concentrations of NaCl, sucrose, soy sauce, worcester sauce and tomato ketchup, and their survival ratios were determined. The E. coli O157:H7 strains showed relatively higher survival ratios in 0.5-1.0 M sucrose, 25% soy sauce and 12.5-50% worcester sauce than the non-pathogenic strains, but slightly lower survival ratios in 0.5-2.0 M NaCl. A noteworthy difference between E. coli O157:H7 and the non-pathogenic strains was that incubation in the presence of 12.5% soy sauce allowed the growth of E. coli O157:H7 strains but reduced the viable cell numbers of non-pathogenic E. coli strains.     

乳酸菌对肠出血性大肠杆菌O157:H7抑制作用的研究

为探讨乳酸菌对肠出血性大肠杆菌O157：H7 ATCC43895(E．Coli O157：H7)的抑制作用，在培养基上进行了研究。将E．Coli O157：H7与干酪乳杆菌干酪亚种、植物乳杆菌、发酵乳杆菌、乳酸乳球菌和瑞士乳杆菌同时接种在培养基中，E．Coli O157：H7的活性不受影响；将E．Coli O157：H7接种到培养了24h的乳酸茵培养液中，E．Coli O157：H7活性显下降。以乳酸调整的低pH值对E．Coli O157：H7有一定的杀灭作用。本研究表明：乳酸菌的代谢产物乳酸对E．Coli O157：H7有杀灭作用。     

副干酪乳杆菌Z17-壳聚糖复配对大肠杆菌O157:H7的抑菌效果及作用机制

目的：研究副干酪乳杆菌Z17-壳聚糖复配对草莓中大肠杆菌O157:H7抑菌活性及作用机制。方法：采用流式细胞术、傅里叶变换红外光谱、拉曼光谱及扫描电子显微镜技术分析副干酪乳杆菌Z17-壳聚糖对大肠杆菌O157:H7细胞膜的影响。结果：质量分数1.0%壳聚糖溶液与副干酪乳杆菌Z17复配处理能有效去除草莓上的大肠杆菌O157:H7,减菌率达99%;壳聚糖溶液与副干酪乳杆菌Z17共同作用3 h使大肠杆菌O157:H7 DNA胞外释放量达（381.00±3.53）ng/μL,细胞膜破损率为58.3%;细胞壁膜中脂肪酸、蛋白、肽聚糖、糖苷环、多糖结构成分被破坏;细胞膜局部位移变薄,大分子物质黏附于菌体细胞表面,细胞表面出现孔洞,胞内物质泄漏,最终导致菌体死亡。结论：副干酪乳杆菌Z17-壳聚糖能够有效地抑制草莓中大肠杆菌O157:H7,其抑菌作用靶点为大肠杆菌O157:H7的细胞膜,研究可为大肠杆菌O157:H7的生物防治提供参考。     

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.     

Factors influencing the detection and enumeration of Escherichia coli O157:H7 on alfalfa seeds.

Isolating Escherichia coli O157:H7 from batches of alfalfa seeds used to produce sprouts implicated in human illness has been difficult, perhaps due to nonhomogenous and very low-level contamination and inaccessibility of the pathogen entrapped in protected areas of the seed coat. We evaluated the effectiveness of various treatments in releasing E. coli O157:H7 from seeds. The influence of homogenization (blending or stomaching for 1 or 2 min), rinsing method (shaking for 5 min), soaking time (0. 1, 3, 6, or 15 h), soaking temperature (4 or 21 degrees C), and the addition of surfactants (0.1%, 0.5%, or 1.0% Tween 80 or Span 20) to rinse water was determined. Blending or stomaching for 1 or 2 min, and soaking for 1 h or longer at 4 or 21 degrees C, respectively, resulted in maximum release of E. coli O157:H7 from seeds. Soaking seeds at 37 degrees C for 15 h increased cell populations of E. coli O157:H7 by approximately 3.6 log10 CFU/g, likely due to bacterial growth. The maximum number of cells released from seeds by rinse water containing 1.0% Span 20 was at 21 degrees C, whereas at 37 degrees C, 0.1% or 0.5% Tween 80 was more effective. Detection of E. coli O157:H7 on seeds stored at 37 degrees C for up to 13 weeks and on sprouts derived from these seeds was compared. E. coli O157:H7 inoculated on seeds at 2.0 log10 CFU/g was detected after storage of seeds for up to 8 weeks at 37 degrees C and in sprouts produced from the seeds. The pathogen was not detected on seeds stored for 13 weeks at 37 degrees C and was not isolated from sprouts produced from these seeds. Identifying seed treatment methods that enhance removal of E. coli O157:H7 from alfalfa seeds can aid the isolation and enumeration of the pathogen on seeds. With a combination of optimal conditions for detecting the pathogen, i.e. soaking seeds for 1 h and pummeling seeds for 1 min, an enrichment step in modified tryptic soy broth (TSB), and the use of immunomagnetic beads for separation of E. coli O157:H7 cells, E. coli O157:H7 was detected in alfalfa seeds incubated at 37 degrees C for up to 8 weeks as effectively as in sprouts produced from the seeds.     

Survival of Escherichia coli O157:H7 in meat product brines containing antimicrobials

Brine solution injection of beef contaminated with Escherichia coli O157:H7 on its surface may lead to internalization of pathogen cells and/or cross-contamination of the brine, which when recirculated, may serve as a source of new product contamination. This study evaluated survival of E. coli O157:H7 in brines formulated without or with antimicrobials. The brines were formulated in sterile distilled water (simulating the composition of freshly prepared brines) or in a nonsterile 3% meat homogenate (simulating the composition of recirculating brines) at concentrations used to moisture-enhance meat to 110% of initial weight, as follows: sodium chloride (NaCl, 5.5%) + sodium tripolyphosphate (STP, 2.75%), NaCl + sodium pyrophosphate (2.75%), or NaCl + STP combined with potassium lactate (PL, 22%), sodium diacetate (SD, 1.65%), PL + SD, lactic acid (3.3%), acetic acid (3.3%), citric acid (3.3%), nisin (0.0165%) + ethylenediamine tetraacetic acid (EDTA, 200 mM), pediocin (11000 AU/mL) + EDTA, sodium metasilicate (2.2%), cetylpyridinium chloride (CPC, 5.5%), or hops beta acids (0.0055%). The brines were inoculated (3 to 4 log CFU/mL) with rifampicin-resistant E. coli O157:H7 (8-strain composite) and stored at 4 or 15 °C (24 to 48 h). Immediate (0 h) pathogen reductions (P < 0.05) of 1.8 to ≥ 2.4 log CFU/mL were observed in brines containing CPC or sodium metasilicate. Furthermore, brines formulated with lactic acid, acetic acid, citric acid, nisin + EDTA, pediocin + EDTA, CPC, sodium metasilicate, or hops beta acids had reductions (P < 0.05) in pathogen levels during storage; however, the extent of pathogen reduction (0.4 to > 2.4 log CFU/mL) depended on the antimicrobial, brine type, and storage temperature and time. These data should be useful in development or improvement of brine formulations for control of E. coli O157:H7 in moisture-enhanced meat products. PRACTICAL APPLICATION: Results of this study should be useful to the meat industry for developing or modifying brine formulations to reduce the risk of E. coli O157:H7 in moisture-enhanced meat products.     

Effects on Escherichia coli O157:H7 and meat starter cultures of bovine lactoferrin in broth and microencapsulated lactoferrin in dry sausage batters

The effects of lactoferrin (LF) alone or with various chelating agents on the growth of 5 strains of Escherichia coli O157:H7 and 7 meat starter cultures were evaluated. E.coli O157:H7 and starter cultures were grown at 13 or 26 degrees C in Lauria (LB) or All Purpose Tween (APT) broths, respectively, with both broths being supplemented with 2.9% NaCl. LF alone prevented the growth of E. coli O157:H7 strains 0627 and 0628 but other strains grew. The antimicrobial effectiveness of LF was enhanced by EDTA but LF alone did not affect the growth of meat starter cultures in broth. However, when LF plus EDTA and sodium bicarbonate (SB) were used the growth of all meat starter cultures except Lactobacillus curvatus was reduced. During dry sausage manufacture with L. curvatus and Staphylococcus carnosus starter cultures the effects of LF, unencapsulated or microencapsulated in paste-like and dried powder forms, in sausage batters with or without EDTA and SB, on the viability of E. coli O157:H7 were examined. The reduction of E. coli O157:H7 during sausage manufacture was significantly enhanced (p<0.05) by all LF treatments. The largest reduction (4.2 log units) was obtained with unencapsulated LF. However, some of the apparent reduction in E.coli O157:H7 numbers with all treatments was due to cell injury rather than lethality, since significantly greater numbers were recovered on APT agar overlaid with the selective medium cefixime-tellurite Sorbitol McConkey agar (ct-SMAC) than on ct-SMAC alone. The narrow spectrum of LF activity and induction of injury rather than inactivation of E. coli O157:H7 limit the effectiveness of this agent against the pathogen in fermented meats.     

In vitro inhibition of Escherichia coli O157:H7 by bifidobacterial strains of human origin

The ability of bifidobacteria isolated from infant feces to inhibit enterohemorrhagic Escherichia coli serotype O157:H7 in vitro and reduce its adhesion to human enterocyte-like Caco-2 cells was evaluated in comparison to American Type Culture Collection bifidobacterial reference strains. Five Bifidobacterium isolates from infant feces were identified and characterized by morphology, fructose-6-phosphate phosphoketolase (F6PPK) assay, polymerase chain reaction using bifidobacterial 16S rDNA specific primers, carbohydrate fermentation patterns, resistance to lysozyme, acid, bile and hydrogen peroxide as well as their ability to inhibit E. coli O157:H7 using the agar spot technique. Infant isolates showed greater resistance to bile, acid, lysozyme and more antimicrobial activity against E. coli O157:H7 than ATCC strains. Two infant isolates identified as B. bifidum RBL 71 and B. bifidum RBL 460 showed good adhesion and significant potential for reducing adhesion of E. coli O157:H7 to Caco-2 cells. This effect was dependent on bifidobacterial cell concentration. These results show that bifidobacteria isolated from infants may be useful for improving probiotic formulae with respect to protection against E. coli O157:H7 infection.     

Influence of sodium chloride on growth of lactic acid bacteria and subsequent destruction of Escherichia coli O157:H7 during processing of Lebanon bologna

Due to undesirable quality changes, Lebanon bologna is often processed at temperatures that do not exceed 48.8 degrees C (120 degrees F). Therefore, it is important to study parameters that influence the destruction of Escherichia coli O157:H7 in Lebanon bologna. The objective of the present study was to determine the influence of curing salts (NaCl and NaNO2) on the destruction of E. coli O157:H7 during Lebanon bologna processing. Fermentation to pH 4.7 at 37.7 degrees C reduced populations of E. coli O157:H7 by approximately 0.3 log10, either in the presence or absence of curing salts. Subsequent destruction of E. coli O157:H7 during heating of fermented product to 46.1 degrees C was significantly reduced by the presence of 3.5% NaCl and 156 ppm NaNO2, compared to product without curing salts (P < 0.01). The presence of a higher level of NaCl (5%) in Lebanon bologna inhibited the growth of lactic acid bacteria (LAB), which yielded product with higher pH (approximately 5.0) and significantly reduced the destruction of E. coli O157:H7 even further (P < 0.05). Lower concentrations of NaCl (0, 2.5%) yielded Lebanon bologna with higher LAB counts and lower pHs, compared to product with 5% NaCl. When lactic acid was used to adjust pH in product containing different levels of NaCl, it was determined that low pH was directly influencing destruction of E. coli O157:H7, not NaCl concentration.     

Autoinducer-2 activity of gram-negative foodborne pathogenic bacteria and its influence on biofilm formation

ABSTRACT:  This study evaluated whether autoinducer-2 (AI-2) activity would be associated with biofilm formation by Salmonella and Escherichia coli O157:H7 strains on food contact surfaces. In study I, a Salmonella Typhimurium DT104 strain and an E . coli O157:H7 strain, both AI-2 positive, were individually inoculated into 50 mL of Luria–Bertani (LB) or LB + 0.5% glucose (LBG) broth, without or with stainless steel or polypropylene ( Salmonella ) coupons. At 0, 14 ( Salmonella ), 24, 48, and 72 h of storage (25 °C), cells in suspension and detached cells from the coupons, obtained by vortexing, were enumerated on tryptic soy agar. In study II, a Salmonella Thompson AI-2-positive strain and an AI-2-negative strain, and an E . coli O157:H7 AI-2-positive strain and an AI-2-negative strain were inoculated into LB broth with stainless steel coupons. Cells were enumerated as in study I. In both studies, AI-2 activity was determined in cell-free supernatants. Cell numbers of S . Typhimurium DT104 on biofilms were higher ( P < 0.05) in LB than those in LBG, while the E . coli O157:H7 strain showed no difference ( P ≥ 0.05) in biofilm cell counts between LB and LBG after storage for 72 h. Both S . Typhimurium DT104 and E . coli O157:H7 strains produced higher ( P < 0.05) AI-2 activity in LBG than LB cell suspensions. Cell counts of AI-2-positive and-negative S . Thompson and E . coli O157:H7 strains were not different ( P ≥ 0.05) within suspensions or coupons (study II). The results indicated that, under the conditions of this study, AI-2 activity of the pathogen strains tested may not have a major influence on biofilm formation on food contact surfaces, which was similar between AI-2-positive and -negative strains.     

鲜切果蔬中4 种病原微生物多重PCR检测技术

研发可同时检测鲜切果蔬中的单核细胞性李斯特菌、鼠伤寒沙门菌、金黄色葡萄球菌和大肠杆菌O157:H7的多重聚合酶链式反应（polymerase chain reaction,PCR）检测方法。根据单核细胞性李斯特菌inlA基因、鼠伤寒沙门菌invA基因、大肠杆菌O157:H7 wzy基因、金黄色葡萄球菌nuc基因设计及筛选出4?对引物。对多重PCR体系及条件进行优化。该方法对单核细胞性李斯特菌、鼠伤寒沙门菌、金黄色葡萄球菌和大肠杆菌O157:H7的检出限分别为3.5×106、1.6×105、2.4×105、4.8×105?CFU/mL。将优化的多重PCR方法对不同接种量富集后验证,结果表明,经过9?h富集后,该方法检出限为1?CFU/mL。该方法在鲜切莴苣、鲜切黄瓜、鲜切木瓜、鲜切哈密瓜中应用同样可扩增出4?条目标菌。因此,利用所建立的多重PCR方法对鲜切果蔬中侵染的病原菌检出限可达到1?CFU/g。该方法相较于传统的培养检测方法具有节约大量的劳力、试剂、时间等优点,检测时间也由原来的5～7?d缩短至9～11?h,对于企业或分析检验中心大批量样品的监测具有指导意义。     

Effects of cetylpyridinium chloride, acidified sodium chlorite, and potassium sorbate on populations of Escherichia coli O157:H7, Listeria monocytogenes, and Staphylococcus aureus on fresh beef

The effects of selected food-grade antimicrobial agents at decreasing the number of pathogenic bacteria on fresh beef were determined. Beef cubes inoculated with Escherichia coli O157:H7, Listeria monocytogenes, or Staphylococcus aureus were sprayed with 0.5% cetylpyridinium chloride (CPC), 0.12% acidified sodium chlorite (ASC), 0.1% potassium sorbate (PS), or an equal mix of any two solutions. The beef samples were placed on absorbent tray pads sprayed with each single or mixed solution, wrapped with polyvinyl chloride film, heat sealed, and stored at 4 degrees C for 2 weeks. Surface sanitization using CPC, ASC, or an equal mix of these two agents effectively reduced microbial numbers on the beef during storage. At day 0, ASC and the CPC-ASC mix reduced the number of E. coli O157:H7 by 2.50 and 1.58 log CFU/cm2, respectively. CPC demonstrated a 3.25-log reduction of L. monocytogenes and a 4.70-log reduction of S. aureus at 14 days. The CPC-PS mix reduced E. coli O157:H7 numbers by 1.46, L. monocytogenes by 2.95, and S. aureus by 4.41 log CFU/cm2 at 14 days. PS alone and the mixed solutions, CPC-ASC, CPC-PS, or ASC-PS, were not as effective as ASC or CPC alone. To effectively reduce E. coli O157:H7, L. monocytogenes, or S. aureus numbers, higher (> 0.1%) concentrations of PS were necessary. Loss of redness and light color of beef surfaces consistently coincided with decreases in pH for ASC-treated beef samples.     

等离子体活化水-苯乳酸协同杀灭大肠杆菌O157:H7作用及机制研究

拟研究等离子体活化水（Plasma-activated water,PAW）与苯乳酸（Phenyllactic acid,PLA）协同处理对大肠杆菌O157:H7的杀灭效果及其作用机制。采用平板计数、扫描电镜、荧光染色等方法研究PAW与PLA协同处理对大肠杆菌O157:H7的杀灭作用及其对细胞形态、细胞膜完整性和胞内活性氧水平等的影响。结果表明,经终浓度为0.125～1.0 mg/mL的PLA处理8 min后,大肠杆菌O157:H7活细胞数未发生显著变化（P>0.05）。经PAW与PLA（终浓度为1.0 mg/mL）协同处理8 min后,大肠杆菌O157:H7降低了5.65 lg CFU/mL,显著高于PAW单独处理组（降低了1.06 lg CFU/mL） （P<0.05）。扫描电镜结果表明,PAW与PLA协同处理可造成细胞形态发生明显变化。与对照组细胞相比,经PAW-PLA（1.0 mg/mL）协同处理8 min后,胞外蛋白含量、细胞膜电位和胞内活性氧分别升高了25.6、0.75和9.53倍（P<0.05）。综上所述,PAW与PLA协同处理能够有效杀灭大肠杆菌O157:H7,这可能与其破坏细胞膜及诱导氧化损伤等有关。本研究为PAW与PLA协同处理在食品保鲜中的应用提供了理论依据。     

Penetration of Escherichia coli O157:H7 into lettuce as influenced by modified atmosphere and temperature.

The effects of temperature and atmospheric oxygen concentration on the respiration rate of iceberg lettuce and Escherichia coli O157:H7 cells attachment to and penetration into damaged lettuce tissues were evaluated. Respiration rate of lettuce decreased as the temperature was reduced from 37 to 10 degrees C. Reducing the temperature further to 4 degrees C did not affect the respiration rate of lettuce. Respiration rate was also reduced by lowering the atmospheric oxygen concentration. Lettuce was submerged in E. coli O157:H7 inoculum at 4, 10, 22, or 37 degrees C under 21 or 2.7% oxygen. Attachment and penetration of E. coli O157:H7 were not related to the respiration rate. The greatest numbers of E. coli O157:H7 cells attached to damaged lettuce tissues at 22 degrees C at both oxygen concentrations. More cells were attached under 21% oxygen than under 2.7% oxygen at each temperature, but this difference was small. Penetration of E. coli O157:H7 into lettuce tissue was determined by immunostaining with a fluorescein isothiocyanate-labeled antibody. Under 21% oxygen, E. coli O157:H7 cells showed greatest penetration when lettuce was held at 4 degrees C, compared to 10, 22. or 37 degrees C, and were detected at an average of 101 microm below the surfaces of cut tissues. However, under 2.7% oxygen, there were no differences in degree of penetration among four incubation temperatures. The degree of E. coli O157:H7 penetration into lettuce tissue at 4 or 22 degrees C was greater under 21% oxygen than under 2.7% oxygen; however, no difference was observed at 37 degrees C. Conditions that promote pathogen penetration into tissue could decrease the effectiveness of decontamination treatments.     

Evaluating lethality of beef roast cooking treatments against Escherichia coli O157:H7

Added salt, seasonings, and phosphates, along with slow- and/or low-temperature cooking impart desirable characteristics to whole-muscle beef, but might enhance Escherichia coli O157:H7 survival. We investigated the effects of added salt, seasoning, and phosphates on E. coli O157:H7 thermotolerance in ground beef, compared E. coli O157:H7 thermotolerance in seasoned roasts and ground beef, and evaluated ground beef-derived D- and z-values for predicting destruction of E. coli O157:H7 in whole-muscle beef cooking. Inoculated seasoned and unseasoned ground beef was heated at constant temperatures of 54.4, 60.0, and 65.5°C to determine D- and z-values, and E. coli O157:H7 survival was monitored in seasoned ground beef during simulated slow cooking. Inoculated, seasoned whole-muscle beef roasts were slow cooked in a commercial smokehouse, and experimentally determined lethality was compared with predicted process lethality. Adding 5% seasoning significantly decreased E. coli O157:H7 thermotolerance in ground beef at 54.4°C, but not at 60 or 65.5°C. Under nonisothermal conditions, E. coli O157:H7 thermotolerance was greater in seasoned whole-muscle beef than in seasoned ground beef. Meeting U.S. Government (U.S. Department of Agriculture, Food Safety and Inspection Service, 1999, Appendix A) whole-muscle beef cooking guidance, which targets Salmonella destruction, would not ensure ≥6.5-log CFU/g reduction of E. coli O157:H7 in ground beef systems, but generally ensured $ 6.5-log CFU/g reduction of this pathogen in seasoned whole-muscle beef. Calculations based on D- and z-values obtained from isothermal ground beef studies increasingly overestimated destruction of E. coli O157:H7 in commercially cooked whole-muscle beef as process severity increased, with a regression line equation of observed reduction = 0.299 (predicted reduction) + 1.4373.     

Use of deodorized yellow mustard powder to control Escherichia coli O157:H7 in dry cured Westphalian ham

Dry cured (uncooked) hams with low water activity and pH ≥5.6 seem a likely food vehicle for Escherichia coli O157:H7. In previous work, isothiocyanates produced from mustard glucosinolates by bacterial myrosinase-like activity converted deodorized mustard into a potent antimicrobial in dry sausage. In this study its value in controlling E. coli O157:H7 survival in Westphalian ham was investigated. Hams were inoculated with a 7.5 log cfu g(-1) cocktail of E. coli O157:H7, 4% or 6% (w/w) deodorized yellow mustard powder was surface applied and monitored 80 d for pathogen survival. In one trial to accelerate formation of isothiocyanate, a Staphylococcus (S.) carnosus meat starter culture was added to hams at 45 d (after salt equilibration). At 21 d, E. coli O157:H7 was reduced by 3 log cfu g(-1) on hams treated with mustard powder compared to only a 1 log cfu g(-1) reduction in the control. By 45 d, mustard powder caused a reduction of >5 log cfu g(-1)E. coli O157:H7, whereas it took 80 d for numbers in control hams to be similarly reduced. Although the commercial process used caused a 5 log cfu g(-1) reduction of E. coli O157:H7 in 80 d, 4% or 6% deodorized mustard accelerated this reduction and the S. carnosus starter culture may have contributed to the maintenance of this effect.     

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.