Behavior of Escherichia coli O157:H7, Listeria monocytogenes, and Salmonella Typhimurium in teewurst, a raw spreadable sausage

The fate of Listeria monocytogenes, Salmonella Typhimurium, or Escherichia coli O157:H7 were separately monitored both in and on teewurst, a traditional raw and spreadable sausage of Germanic origin. Multi-strain cocktails of each pathogen (ca. 5.0 log CFU/g) were used to separately inoculate teewurst that was subsequently stored at 1.5, 4, 10, and 21 °C. When inoculated into commercially-prepared batter just prior to stuffing, in general, the higher the storage temperature, the greater the lethality. Depending on the storage temperature, pathogen levels in the batter decreased by 2.3 to 3.4, ca. 3.8, and 2.2 to 3.6 log CFU/g for E. coli O157:H7, S. Typhimurium, and L. monocytogenes, respectively, during storage for 30 days. When inoculated onto both the top and bottom faces of sliced commercially-prepared finished product, the results for all four temperatures showed a decrease of 0.9 to 1.4, 1.4 to 1.8, and 2.2 to 3.0 log CFU/g for E. coli O157:H7, S. Typhimurium, and L. monocytogenes, respectively, over the course of 21 days. With the possible exceptions for salt and carbohydrate levels, chemical analyses of teewurst purchased from five commercial manufacturers revealed only subtle differences in proximate composition for this product type. Our data establish that teewurst does not provide a favourable environment for the survival of E. coli O157:H7, S. Typhimurium, or L. monocytogenes inoculated either into or onto the product.     

Resistance of Listeria monocytogenes, Escherichia coli O157:H7 and Campylobacter jejuni after exposure to repetitive cycles of mild bactericidal treatments

While maintaining nutritional and sensorial attributes of fresh foods mild processing technologies generally deliver microbiologically perishable food products. Currently little information exists on possible increase in the resistance of pathogens after repetitive exposure to mild (sub-lethal) treatments. Multiple strain-cocktails of Listeria monocytogenes, Escherichia coli O157:H7 and Campylobacter jejuni were exposed to 20 consecutive cycles of sub-lethal inactivation by three different techniques. Used techniques comprised inactivation with lactic acid (LA), chlorine dioxide (ClO₂) and intense light pulses (ILP). Results showed that the selection of resistant cells was both species and technique dependent. While repetitive cycles of ClO₂ treatment did not result in increased resistance, repetitive inactivation with LA yielded L. monocytogenes culture of higher resistance in comparison to the parental culture. The increased resistance, expressed as decreased level of reduction in bacterial counts in subsequent inactivation cycles, was also observed with ILP for both L. monocytogenes and E. coli O157:H7 strains. Visual trend observations were confirmed through statistical linear regression analysis. No such effects were noted for C. jejuni which became undetectable after first 2–5 cycles. Current findings indicate the ability of foodborne pathogens to adapt to mild bactericidal treatments creating new challenges in risk assessment and more specifically in hazard analysis.     

The prevalence of Listeria, Salmonella, Escherichia coli and E. coli O157:H7 on bison carcasses during processing

Bison meat is a relatively new, emerging meat species gaining increased popularity in the US and European meat markets, but little is known of its microflora or pathogens that may be present. This study was carried out to determine the incidence of the foodborne pathogens Listeria, Salmonella, Escherichia coli/E. coli O157:H7 on slaughtered bison and to evaluate the bison slaughter process. Bison carcass sampling was carried out at monthly intervals over a period of 1 year at a Bison processing facility in the Midwestern United States. A total of 355 Bison carcasses were sampled by surface swabbing the carcasses at five points on the production line: pre-dehiding, post-evisceration, post-USDA inspection, post-washing and 24 h chilled carcass. Overall, the prevalence of Listeria spp., Salmonella spp., E. coli and E. coli O157:H7 was 18.3%, 3.94%, 38.3% and 1.13%, respectively. The prevalence of Listeria spp. at each sampling point tested was 42.24%, 18.1%, 6.03%, 1.72% and 3.77% while the prevalence of E. coli at each sampling point was: 88.79%, 73.28%, 52.59%, 56.89% and 11.3%, respectively. The data obtained suggests that current antimicrobial intervention strategies used at the plant are relatively effective in reducing Listeria and E. coli contamination on bison carcasses to some extent, however further study is required to determine the influence of current slaughter practices on carcass contamination. The data reported in this study to the authors’ knowledge is some of the first information reporting on the bacteriological status of Bison, and provides some useful baseline information for future research.     

基于全基因组测序技术的食品分离致泻大肠埃希菌的分子特征及耐药性研究

目的 了解上海市肉品和水产品中分离致泻大肠埃希菌（DEC）的生物学特征及耐药性,为防控由该菌引起的食源性疾病提供科学依据。方法对食品分离DEC菌株进行全基因组测序及药物敏感性试验,利用BioNumerics软件对全基因组测序数据进行拼接,利用拼接序列开展多位点序列分型、毒力基因和耐药基因分析。结果本研究中56株DEC菌株中肠道聚集性大肠埃希菌（EAEC）占比最高,达73.2%,且以astA基因为主（90.2%）。56株DEC分为37个ST型,显示高度多样性。DEC菌株对喹诺酮类抗生素耐药性较高（64.3%）,其次是对氨基糖苷类、β-内酰胺类抗生素和四环素类抗生素耐药,且多重耐药性菌株占48.2%,耐药基因相应的以喹诺酮类、氨基糖苷类、β-内酰胺类抗生素耐药基因为主,且大多数对抗生素耐药的菌株均携带其相应的耐药基因。结论 EAEC是上海市食品中分离DEC菌株的主要型别,对喹诺酮类、β-内酰胺类、氨基糖苷类抗生素的耐药率较高,且携带相应的耐药基因,全基因组测序技术可应用于DEC的分子生物学监测中,为疾病预防控制提供科学依据。     

Models of the behavior of Escherichia coli O157:H7 in raw sterile ground beef stored at 5 to 46 °C

Escherichia coli O157:H7 can contaminate raw ground beef and cause serious human foodborne illness. Previous reports describe the behavior of E. coli O157:H7 in ground beef under different storage conditions; however, models are lacking for the pathogen's behavior in raw ground beef stored over a broad range of temperature. Using sterile irradiated raw ground beef, the behavioral kinetics of 10 individual E. coli O157:H7 strains and/or a 5- or 10-strain cocktail were measured at storage temperatures from 5° to 46 °C. Growth occurred from 6 to 45 °C. Although lag phase duration (LPD) decreased from 10.5 to 45 °C, no lag phase was observed at 6, 8, or 10 °C. The specific growth rate (SGR) increased from 6 to 42 °C then declined up to 45 °C. In contrast to these profiles, the maximum population density (MPD) declined with increasing temperature, from approximately 9.7 to 8.2 log cfu/g. Bias (B_f) and accuracy (A_f) factors for an E. coli O157:H7 broth-based aerobic growth model (10 to 42 °C) applied to the observations in ground beef were 1.05, 2.70, 1.00 and 1.29, 2.87, 1.03, for SGR, LPD and MPD, respectively. New secondary models increased the accuracy of predictions (5 to 45 °C), with B_f and A_f for SGR, LPD, and MPD of 1.00, 1.06, and 1.00 and 1.14, 1.33, and 1.02, respectively. These new models offer improved tools for designing and implementing food safety systems and assessing the impact of E. coli O157:H7 disease.     

Effects of ionizing irradiation and hydrostatic pressure on Escherichia coli O157:H7 inactivation, chemical composition, and sensory acceptability of ground beef patties

A randomized complete block design with three replications was utilized to determine the effects of ionizing irradiation and hydrostatic pressure on the inactivation of Escherichia coli O157:H7, volatile composition, and consumer acceptability (n = 155) of frozen ground beef patties. E-beam and X-ray irradiation (2 kGy) inactivated E. coli O157:H7 below the limit of detection, while hydrostatic pressure treatment (300 mPa for 5 min at 4 °C) did not inactivate this pathogen. Solid-phase microextraction (SPME) was used to extract volatile compounds from treated ground beef patties. Irradiation and hydrostatic pressure altered the volatile composition (P < 0.05) of the ground beef patties in respect to radiolytic products. However, results were inconclusive on whether these differences were great enough to use this method to differentiate between irradiated and non-irradiated samples in a commercial setting. Irradiation did not affect (P > 0.05) consumer acceptability of ground beef patties when compared to untreated samples, but hydrostatic pressure caused decreased acceptability (P < 0.05) when compared to other treatments.     

Effects of salt, acid, and MSG on cold storage survival and subsequent acid tolerance of Escherichia coli O157:H7

The combined effects of salt, monosodium glutamate (MSG), and pH on cold storage survival and subsequent acid tolerance of Escherichia coli O157:H7 were determined. Cold storage survival was evaluated in tryptic soy broth (TSB) with combinations of pH (7.2, 5.0, or 4.0), MSG (0, 0.5, 1%) and salt (0, 2, 4%). Survival through 21 d at 5°C and acid tolerance in simulated gastric fluid were evaluated weekly. In separate experiments, strains were tested individually for the effect of growth in the presence of MSG on subsequent acid resistance and for the ability of MSG to impact growth under acid conditions. The impact of salt on cold storage survival was greater at pH 4.0 and 7.0 compared to pH 5.0. MSG did not enhance cold storage survival. The presence of MSG alone enhanced acid tolerance following cold storage at pH 5.0 and 7.2 compared to control cells. At pH 4.0, MSG alone enhanced acid tolerance compared to control cells following 21 days cold storage. Overnight growth in TSB containing MSG did not affect subsequent acid tolerance in acidified TSB (pH 2.0). The presence of MSG in TSB (37°C) did not enable growth at lower pH.     

Effect of X-ray treatments on inoculated Escherichia coli O157: H7, Salmonella enterica, Shigella flexneri and Vibrio parahaemolyticus in ready-to-eat shrimp

This study was conducted to evaluate the inactivation effect of X-ray treatments on Escherichia coli O157: H7, Salmonella enteric (S. enterica), Shigella flexneri (S. flexneri) and Vibrio parahaemolyticus (V. parahaemolyticus) artificially inoculated in ready-to-eat (RTE) shrimp. A mixed culture of three strains of each tested pathogen was used to inoculate RTE shrimp. The shrimp samples were inoculated individually with selected pathogenic bacteria then aseptically placed in sterile plastic cups and air-dried at 22 °C for 30 min (to allow bacterial attachment) in the biosafety cabinet prior to X-ray treatments. The inoculated shrimp samples were then placed in sterilized bags and treated with 0.1, 0.2, 0.3, 0.5, 0.75, 1.0, 2.0, 3.0 and 4.0 kGy X-ray at ambient temperature (22 °C and 60% relative humidity). Surviving bacterial populations were evaluated using a non-selective medium (TSA) with the appropriate selective medium overlay for each bacterium; CT-SMAC agar for E. coli O157: H7, XLD for S. enterica and S. flexneri and TCBS for V. parahaemolyticus. More than a 6 log CFU reduction of E. coli O157: H7, S. enterica, S. flexneri and V. parahaemolyticus was achieved with 2.0, 4.0, 3.0 and 3.0 kGy X-ray, respectively. Furthermore, treatment with 0.75 kGy X-ray significantly reduced the initial microflora on RTE shrimp samples from 3.8 ± 0.2 log CFU g⁻¹ to less than detectable limit (<1.0 log CFU g⁻¹).     

The prevalence of Escherichia coli O157 and O157:H7 in ground beef and raw meatball by immunomagnetic separation and the detection of virulence genes using multiplex PCR

The present study was conducted to investigate the presence of Escherichia coli O157 and O157:H7 strains and to detect the presence of the stx1, stx2, and eaeA genes in isolates derived from 200 samples (100 samples from fresh ground beef and 100 samples from raw meatball). The samples were purchased from the Samsun Province in Turkey, over a period of 1 year. Enrichment-based immunomagnetic separation and multiplex polymerase chain reaction were applied for these analyses. E. coli O157 was detected in five of the 200 (2.5%) samples tested (one isolated from ground beef and four from meatball samples), whereas E. coli O157: H7 was not detected in any sample. During the analysis, eight strains of E. coli O157 were obtained. The genes stx1, stx2, and eaeA were detected in two E. coli O157 isolates obtained from two meatball samples, whereas only the eaeA and the stx2 genes were detected in four E. coli O157 strains that were isolated from one meatball sample. None of the stx1, stx2, and eaeA was detected in the E. coli O157 isolates obtained from the ground beef and the one meatball samples.     

Behaviour of Escherichia coli O157:H7 during the fermentation of Datta and Awaze, traditional Ethiopian fermented condiments, and during product storage at ambient and refrigeration temperatures

The survival of E. coli O157:H7 in fermenting foods and its prolonged survival in refrigerated fermented foods is documented. This prompted the study to evaluate survival of E. coli O157:H7 during the fermentation of Datta and Awaze, traditional Ethiopian condiments. Datta was prepared by wet milling a variety of spices along with green or red chilli and fermenting it by lactic acid bacteria. Awaze is a slurry made of red pepper, garlic and ginger to which various other spices were added and fermented by lactic acid bacteria (LAB) and yeasts. The Datta or Awaze slurry was separately inoculated with three strains of E. coli O157:H7 and the fermentation was allowed to proceed at ambient (20–25°C) temperatures for 7 days. When fermenting Datta or Awaze was initially inoculated at low inoculum level (3 log cfu/g), the test strains were not recovered after 24 h of fermentation. At higher initial inoculum level (6 log cfu/g), however, counts of the test strains in Datta at day 7 were less by about 1.5 log unit than the initial inoculum level. In fermenting Awaze, all test strains were completely eliminated in 7 days. The pH of the fermenting green and red Datta was reduced from 5.2 to 4.4 and that of Awaze dropped from 4.9 to 3.8 during this time. In another experiment, the fermented products were separately inoculated with the E. coli O157:H7 test strains at levels of 6 log cfu/g and incubated at ambient and refrigeration (4°C) temperatures for 7 days. In fermented Datta, two of the three strains were not recovered by enrichment after 6 days of storage at ambient temperatures. In fermented Awaze, all strains were below countable levels at day 5, but could still be recovered by enrichment at day 7. At refrigeration storage, counts of the test strains in Datta and Awaze products were <3 log cfu/g at day 7. The inhibition of our E. coli O157:H7 test strains in Datta and Awaze may be due to the antimicrobial activity of spices and other metabolites produced by LAB which may be effective at low pH.     

Prevalence of tetracycline resistance and genotypic analysis of populations of Escherichia coli from animals, carcasses and cuts processed at a pig slaughterhouse

A Danish pig slaughterhouse was visited in this study to investigate the impact of carcass processing on prevalence of tetracycline-resistant Escherichia coli, and to identify the origins of carcass contaminations with E. coli by assessing genetic diversity of E. coli populations on carcasses. A total of 105 carcasses were sampled at five sequential stages: after stunning, after scalding, after splitting, after cooling and after cutting. Total and tetracycline-resistant E. coli were counted for each sample and tetracycline resistance prevalence per sample was calculated by the fraction of tetracycline-resistant E. coli out of total E. coli. From 15 repeatedly sampled carcasses, 422 E. coli isolates from faeces, stunned carcasses, split carcasses and chilled carcasses were examined by pulse-field gel electrophoresis (PFGE) and tested for antimicrobial susceptibility. The results showed that E. coli counts and the prevalence of tetracycline-resistant E. coli per sample were both progressively reduced after each sampling stage. PFGE analysis showed that E. coli populations from stunned carcasses were highly genetically diverse, compared with those from split carcasses and faeces. Thirteen carcasses (87%) were contaminated with E. coli that were also isolated from faeces of either the same or other pigs slaughtered on the same day; and 80% of stunned carcasses shared the same E. coli PFGE subtypes. The results suggest that some carcass processing steps in the slaughterhouse were effective in reducing both E. coli numbers and the tetracycline resistance prevalence in E. coli on carcasses. Faeces from the same or other pigs slaughtered on the same day were likely to be an important source of E. coli carcass contamination. Combined data from E. coli enumeration, PFGE typing and antimicrobial susceptibility testing suggest that tetracycline-susceptible E. coli probably persisted better compared to resistant ones during the carcass processing.     

基于dsDNA-CuNCs的荧光ELISA检测牛奶中的E.coli O157:H7

目的:建立了一种灵敏检测牛奶中大肠杆菌O157:H7的新型荧光酶联免疫吸附方法。方法:以碱性磷酸酶水解焦磷酸盐-Cu²⁺配位复合物,释放出Cu²⁺形成铜纳米簇作为信号报告探针,通过对关键因素Cu²⁺浓度、焦磷酸盐浓度、DNA模板的浓度和长度进行优化。结果:在最优条件下,大肠杆菌O157:H7的菌数为5×10⁴～1×10⁸ CFU/mL时,与荧光信号值有较好的线性关系(R²=0.980 8),最低检出限为2.4×10⁴ CFU/mL。结论:该方法成功地应用于低脂牛奶和脱脂牛奶样本中大肠杆菌O157:H7的测定,平均回收率为92.2%～108.5%,相对标准偏差为4.9%～10.4%。     

The occurrence of Escherichia coli O157 in/on faeces,carcasses and fresh meats from cattle

The aim of this study was to investigate whether Escherichia coli O157 is present in/on raw beef in Serbia. Correlated faecal and carcasses samples from 115 slaughtered cattle plus 26 uncorrelated carcass samples were examined. E. coli O157 detection and identification was performed using selective enrichment and immunomagnetic separation followed by selective media-plating and biochemical tests.     

肉制品中致泻大肠埃希菌的分子特征分析

目的 了解国内肉制品中致泻大肠埃希菌（DEC）的流行特征。方法 运用全基因组测序技术对86株DEC进行分子特征分析,明确优势病理类型、序列型和血清型。通过全基因组单核苷酸多态性分析,确定我国肉制品来源DEC菌株之间的系统发育关系。结果 肉制品中致泻大肠埃希菌的病理类型以EAEC为主,86株DEC可分为8种毒力基因型,包括48个ST型（包括6个新ST型）和55个O:H血清型;ST11和CC10为优势序列型和克隆复合体,O157、O15和O6为优势血清群。DEC菌株间表现为高度的遗传异质性,相同病理类型的同源性较低,处在不同的进化分支上。结论 DEC的病理类型与ST型及血清型间未见对应关系,通过对ST型及血清型的监测不能直接对病理类型进行判断,但数量最多的ST型及血清型揭示了DEC的主要危害特征与防控点。可根据全基因组测序结果补充和优化DEC的判定方法,为今后DEC的溯源及流行病学调查提供数据支撑。     

鸡源大肠埃希氏菌mcr-1基因携带及分析

目的 了解在农业农村部禁止使用多黏菌素作为动物促生长使用后四川部分地区鸡源大肠埃希氏菌（E.coli）mcr-1基因的携带情况,为制定进一步防控措施提供依据。方法 采集四川部分地区市场售卖点肉鸡直肠拭子,用含有多黏菌素（终浓度4 μg/mL）的EC肉汤增菌接种含多黏菌素（终浓度4 μg/mL）的麦康凯平板,挑取可疑菌落,采用PCR方法鉴定菌株并检测mcr-1基因;微量肉汤稀释法测定mcr-1基因阳性菌株对临床常见抗菌药物耐药情况。脉冲场凝胶电泳（PFGE）对mcr-1基因阳性菌株进行同源分析。耐药基因质粒结合实验验证mcr-1基因传播途径。结果 从70份肉鸡样本中的13份检出mcr-1基因阳性大肠埃希氏菌,检出率18.57%（13/70）,对实验的13种抗生素,除13株mcr-1阳性菌株对头孢西丁有12株敏感以外,对其他抗生素都表现出不同程度的耐药,其中四环素和甲氧苄啶/磺胺甲恶唑耐药率最高,达到了100%（13/13）;其次是氨苄西林和氯霉素,耐药率为84.62%（11/13）。PFGE显示13株mcr-1阳性大肠埃希氏菌分属13个不同的型别;质粒结合实验显示mcr-1基因能够通过质粒传播。结论 mcr-1基因在鸡大肠内大肠杆菌中检测率比较高,且鸡大肠中mcr-1阳性大肠埃希氏菌的耐药情况比较严重。     

Adaptation of Escherichia coli O157:H7 to acid in traditional and commercial goat milk amasi

Acid resistance of Escherichia coli O157:H7 strains UT 10 and UT 15 were determined in traditional Amasi fermented for 3 days at ambient temperature (ca 30 °C) and commercial Amasi fermented at 30 °C for 24 h and stored at 7 °C for 2 days. Escherichia coli O157:H7 counts in commercial Amasi were detected at 2.7 log₁₀ cfu/ml after 3 days while those in traditional Amasi could not be detected after the same period. There was no significant difference (p ? 0.05) in the survival of acid adapted (AA) and non-adapted (NA) E. coli O157:H7 in traditional Amasi, while in commercial Amasi, the NA strain survived significantly (p ? 0.05) better than its AA counterpart. Regardless of prior adaptation to acid, E. coli O157:H7 can survive during fermentation and storage of fermented goat milk Amasi. Also, the fermentation time, pH and storage temperature affects the survival of E. coli O157:H7 in the fermented milk.     

Occurrence of Escherichia coli O157, O111 and O26 in raw ewe's milk and performance of two enrichment broths and two plating media used for its assessment

The occurrence of Escherichia coli O157, O111 and O26 in 159 raw ewe's milk samples was examined. Sample-aliquots were incubated simultaneously in TSB added with yeast extract (YETSB) and mTSB with novobiocin (N-mTSB). Serogroup-specific immunomagnetic separation (IMS) was then used and IMS beads were plated in a cefixime tellurite (CT)-containing media (CT-SMAC, CT-SBMAC and CT-RMAC for E. coli O157, O111 and O26, respectively) and E. coli O157:H7 chromogenic ID agar. A sweep of confluent growth from each medium was examined for the presence of E. coli O157 and O111 using PCR, and for E. coli O26 using a latex agglutination test. Enumeration of E. coli O157 and O111 was performed in the samples tested positive for the correspondent serogroup using the most probable number (MPN) method combined with PCR. Percentage occurrences of E. coli O157, O111 and O26 were 18.2, 8.2 and 5.7, respectively. Mean E. coli O157 and O111 levels were 0.22 and < 0.04 MPN/mL, respectively. Enrichment in YETSB resulted in higher detection rates of E. coli O157 and O26 than in N-mTSB. When YETSB was used as enrichment broth and for these last two serogroups, the analysis of the confluent growth from the CT-media gave more positive results than that from E. coli O157:H7-ID medium.     

2019—2021年武汉市致泻大肠埃希菌分子分型与耐药性研究

目的 了解2019—2021年湖北省武汉市腹泻患者来源致泻大肠埃希菌的毒力基因分布、耐药情况以及种群多样性。方法 定期收集来自武汉市5家医疗机构的致泻大肠埃希菌菌株并通过生化反应和飞行时间质谱进行确认。对经确认的菌株进行药敏试验以及多重PCR检测毒力基因。采用脉冲场凝胶电泳技术和多位点序列分型技术对收集的菌株进行分子分型。通过聚类比对和构建最小生成树进行同源性分析。结果 收集到59株致泻大肠埃希菌,共检出3种基因型别。其中检出产肠毒素大肠埃希菌（ETEC）29株,占比最高为49.15%;肠集聚性大肠埃希菌（EAEC）、肠致病性大肠埃希菌（EPEC）各检出15株,占比均为25.42%。59株致泻性大肠埃希菌对除多黏菌素E外的11种抗生素表现出不同程度的耐药,对氨苄西林（67.80%）、萘啶酸（61.02%）、四环素（45.76%）、复方新诺明（37.29%）、头孢噻肟（30.51%）、氯霉素（13.56%）表现出较高的耐药性。EAEC和EPEC均存在14种不同的脉冲场凝胶电泳带型,均可被分为11种不同的ST型别。ETEC存在28种不同的脉冲场凝胶电泳带型,可被分为10种不同的ST型别,且超过50%的ETEC属于同一种优势克隆复合体CC-10。结论 武汉市食源性致泻大肠埃希菌的污染长期存在且耐药情况严重,其中EAEC和EPEC型别多样,ETEC的优势克隆复合体CC-10被广泛检出。     

Treatment of Escherichia coli O157:H7 with lactic acid, neutralized electrolyzed oxidizing water and chlorine dioxide followed by growth under sub-optimal conditions of temperature, pH and modified atmosphere

The utilization of sub-lethal decontamination treatments gains more and more interest due to the increased consumers' demand for fresh, minimally processed and convenient food products. These products rely on cold chain and hurdle (combination) technology to provide microbiological safety and quality during their shelf life. To investigate the ability of surviving cells to resuscitate and grow in a food simulating environment, sub-lethal decontamination treatments were coupled with subsequent storage under sub-optimal growth conditions. For this purpose chlorine dioxide (ClO₂) and neutralized electrolyzed oxidizing water (NEW)-treated cultures of Escherichia coli O157:H7 were inoculated in TSB-YE of pH 5.8 and a_w 0.99, and stored at 10 °C, 12.5 °C and 15 °C, under four different atmospheres (0%, 30% and 60% CO₂ balanced with N₂, and air). Due to the severity of injury, lactic acid-treated cells were inoculated in TSB-YE pH 7.0. Data obtained reveal that the fraction of sub-lethally injured E. coli O157:H7 undergoes an additional inhibitory effect during the storage period under of sub-optimal conditions. Observed extension in the lag growth phase was a direct consequence prior sub-lethal injury. The effects of liquid ClO₂ and NEW were less pronounced in comparison to lactic acid. The current study signifies the potential utilization of appropriate combination of different extrinsic and intrinsic factors in the elimination or growth inhibition of food-borne pathogens.     

Comparison of enrichment procedures for isolation of Escherichia coli O157:H7 from ground beef and radish sprouts

Enrichment procedures using Tryptic soy broth (TSB), modified TSB (mTSB), modified E. coli broth with novobiocin (mEC+n), mTSB (without novobiocin) with vancomycin, cefixime and cefsulodin (mTSB-VCC), or TSB with cefixime, tellurite and vancomycin (TSB-CTV) were evaluated by determining the rate of successful isolation of fifteen Escherichia coli O157:H7 strains from inoculated broth containing ground beef or radish sprout extract. E. coli O157:H7 tended to be isolated more efficiently after enrichment with TSB, mTSB and mEC+n than with the other broths. In order to identify the most efficient enrichmemt condition using these broths, E. coli O157:H7 were inoculated into 25 g ground beef or radish sprouts, which were then homogenized in 225 ml broth and incubated static at 37°C or 42°C for 6 h or 18 h. Attempts were made to isolate the inoculated bacteria by plating method in combination with the immunomagnetic separation method. The most effective enrichment condition was incubation in mTSB or mEC+n at 42°C for 18 h for ground beef, and in mEC+n at 42°C for 18 h for radish sprouts.