The bactericidal activity of acidic electrolyzed oxidizing water against Escherichia coli O157:H7, Salmonella Typhimurium,and Listeria monocytogenes on raw fish,chicken and beef surfaces

The bactericidal efficacy of acidic electrolyzed oxidizing water (AC-EW) (pH = 2.30, free chlorine = 38 ppm) and sterile distilled water (DW) on three pathogens (Escherichia coli O157:H7 Salmonella Typhimurium, and Listeria monocytogenes) inoculated on raw trout skin, chicken legs and beef meat surfaces was evaluated. The decontaminating effect of AC-EW and DW was tested for 0 (control), 1, 3, 5 and 10 min at 22 °C. AC-EW significantly (P < 0.05) reduced the three pathogens in the inoculated samples compared to the control and DW. The level of reduction ranged between ca.1.5–1.6 logs for E. coli O157:H7 and S. Typhimurium in the inoculated foods. However, AC-EW exhibited less bactericidal effect against L. monocytogenes (1.1–1.3 logs reduction). AC-EW elicited about 1.6–2.0 log reduction in the total mesophilic count. Similar treatment with DW reduced pathogens load by ca. 0.2–1.0 log reduction and total mesophiles by ca. 0.5–0.7 logs. No complete elimination of the three pathogens was obtained using AC-EW possibly because of the level of organic matter and blood moving from food samples to the AC-EW solution. This study demonstrates that AC-EW could considerably reduce common foodborne pathogens in fish, chicken and beef products.     

Adherence of cold-adapted Escherichia coli O157:H7 to stainless steel and glass surfaces

The effects of previous cold-induced cell elongation on adherence of Escherichia coli O157:H7 to glass slides and stainless steel surfaces was evaluated at 4 °C for ≤48 h. Planktonic E. coli O157:H7 with and without cold adaptation were prepared at 15 and 37 °C, respectively, and planktonic E. coli O157:H7 containing elongated (>4 ≤ 10 μm) and filamentous (>10 μm) cells were prepared at 6 °C. Despite morphological differences in planktonic E. coli O157:H7 preparations, all three cell types attached to a greater extent to glass than to the stainless steel surfaces. E. coli O157:H7 cells adapted to growth at 15 °C attached better to both glass and stainless steel surfaces (3.2 and 2.6 log cfu/cm², respectively) than cells of the other treatments at ≥24 h. Cells adapted at 6 °C attached to glass slides and stainless steel coupons at levels of 3.0 and 1.8 log cfu/cm², respectively, while E. coli O157:H7 cells grown at 37 °C attached to these surfaces at levels of 2.0 and 1.7 log cfu/cm², respectively. No further attachment of cells from any of the treatments was noted between 24 and 48 h at 4 °C. These results suggest that E. coli O157:H7 cells adapted at 6 °C–15 °C have greater potential to attach to food contact surfaces than those grown at higher temperature. The enhanced biofilm-forming ability of 6 °C or 15 °C-adapted, elongated and filamentous E. coli O157:H7 cells did not appear to be related to the greater entanglement of longer cells within biofilm matrices.     

Comparative simulation of Escherichia coli O157:H7 behaviour in packaged fresh-cut lettuce distributed in a typical Canadian supply chain in the summer and winter

The ability to predict the risk associated with Escherichia coli O157:H7 in packaged fresh-cut lettuce hinges on the availability of realistic times and temperatures encountered in commercial supply chains. We report here on temperature profiles measured in winter and summer months in a retail supply chain and their predicted impact on the fate of the pathogen in fresh-cut lettuce. Time and temperature data were recorded in individual packages within cases of lettuce in the bottom, middle and top layers of pallets distributed from a processing facility to retail storage. Measurements indicated there were occasional increases in temperature during either season and that temperatures were ≥5 °C for longer periods of time during the summer. A stochastic simulation model based on time and temperature distributions was constructed in @RISK™ to predict the fate of E. coli O157:H7. The output from the model demonstrated a range of possible outcomes for the time-temperature profiles measured in the commercial supply chain, ranging from slight growth to die-off. The outputs of the stochastic simulations were similar to analytical simulations based on actual times and temperatures experienced by product in the supply chain. The distributions presented in the current model could be incorporated in quantitative risk assessments to improve predictions about the prevalence and fate of E. coli O157:H7 in fresh-cut lettuce supply chains.     

Development of a controlling method for Escherichia coli O157:H7 and Salmonella spp. in fresh market beef by using polylysine and modified atmosphere packaging

Escherichia coli O157:H7 and Salmonella spp. often contaminate fresh beef. In Japan, an E coli outbreak caused by raw beef made 181 people ill and 5 individuals dead in 2011. Responding to this outbreak, an effective sterilization method for fresh beef is expected to be developed. In this study, ε-polylysine combined with CO₂-packaging method was examined for controlling these pathogens in fresh beef. At an incubation temperature of 4 °C, approximately 4.3 log and 2.4 log reduction in bacterial numbers were observed after 7-day incubation for E. coli O157:H7 and Salmonella, respectively, in ε-polylysine-added beef. When effectiveness of CO₂-packaging combined with ε-polylysine was investigated, CO₂ did not have additional inhibiting effect on bacterial growth compared to only-ε-polylysine-treated samples when incubated at 4 °C. However, effectiveness of CO₂ was observed when incubated at 10 °C where approximately 2.9 log and 4.4 log reduction in E. coli cell numbers were observed in only-ε-polylysine-treated samples and polylysine- and CO₂-treated group, respectively, and approximately 1.7 log and 3.5 log reduction in Salmonella cell numbers were observed in only-ε-polylysine-treated samples and polylysine and CO₂-treated group, respectively. This study confirmed that ε-polylysine or ε-polylysine combined with CO₂ packaging are effective in preventing foodborne diseases caused by raw beef.     

Detection of Escherichia coli O157:H7 in ground beef using immunomagnetic separation and multiplex PCR

In the study 251 fresh ground beef samples sold in Ankara were analyzed to evaluate the prevalence of Escherichia coli O157:H7 by immunomagnetic separation (IMS) based cultivation technique. Virulence factors of the isolates were determined by multiplex PCR. Nineteen (7.6%) of 251 ground beef samples were found as contaminated with E. coli O157. By PCR analyse in two of the isolates fliC_h7 gene was detected and identified as E. coli O157:H7. According to the multiplex PCR one of the isolate has all stx₁, stx₂, eaeA, hly and fliC_h7 genes and the other has stx₁, eaeA, hly and fliC_h7 genes.     

Modeling the inactivation of Escherichia coli O157:H7 and Uropathogenic E. coli in ground beef by high pressure processing and citral

Escherichia coli O157:H7 are a well-known intestinal foodborne pathogen which were responsible for numerous foodborne illness outbreaks. Uropathogenic E. coli (UPEC) are common contaminants in meat and poultry, and may cause urinary tract infections after colonizing the gastrointestinal tract followed by accidental transfer of contaminated feces from the anus to the urethra. High pressure processing (HPP) has been demonstrated an effective means in reducing pathogenic E. coli levels in meat and poultry. Citral, an antimicrobial, also demonstrated some inactivation effect on pathogenic E. coli in ground beef (ca. 0.5–1.0 log CFU/g reduction at 1% w/w without HPP). With HPP alone, to achieve 5 log CFU/g reduction required a 500 MPa level and 15 min (for both O157:H7 and UPEC). However, 1% of citral addition may lower the pressure requirement to 380 MPa and 15 min which could reduce the food quality damage. To effectively inactivate E. coli O157:H7 and UPEC in meat, high pressure processing (HPP) in combination with the antimicrobial citral was studied. Ground beef inoculated with E. coli O157:H7 or UPEC were treated at different HPP conditions (250–350 MPa; 10–20 min), and citral (0.75–1.25%, w/w) following a central composite experimental design. Quadratic linear regression equations were developed to describe and predict the reductions of E. coli O157:H7 (R² = 0.93, p < 0.001) and UPEC (R² = 0.92, p < 0.001). Dimensionless nonlinear models consisting of three impact factors were also developed and compared with the linear models. These models were experimentally validated. Citral enhanced the inactivation of pathogenic E. coli, increasing the effectiveness of the HPP process. The models may assist the food industry and regulatory agencies in risk assessment of E. coli O157:H7 and UPEC on ground meats.     

Inactivation of Escherichia coli O157:H7 by high pressure carbon dioxide combined with nisin in physiological saline,phosphate-buffered saline and carrot juice

The individual and combined effects of high pressure carbon dioxide (HPCD) and nisin (200 IU/mL) on the inactivation of Escherichia coli O157:H7 suspended in physiological saline (PS, pH 5.60), phosphate-buffered saline (PBS, pH 5.60 or 7.00) or carrot juice (pH 6.80) were evaluated. The pressure in this study was 5 and 8 MPa, the temperature was 25 °C–45 °C, and the treatment time was 5–65 min. Inactivation of cells in PS (pH 5.60) by HPCD followed first order kinetics, the k (the inactivation rates) increased while the D (decimal reduction time) decreased in the presence of nisin, however, the acid solution dissolving nisin rather than nisin itself played a prominent role in this combination effect with HPCD in PS buffer. The inactivation kinetics of cells in PBS (pH 5.60 or 7.00) and carrot juice (pH 6.80) by HPCD followed slow-to-fast two-stage kinetics and was fitted by the modified Gompertz equation. The M (the time at which the absolute death rate is maximum) significantly decreased in the presence of nisin. HPCD enhanced the sensitization of E. coli to nisin and the time for the complete inactivation was shortened by 2.5–5 min in PBS buffer and carrot juice by combination of HPCD and nisin (HPCD + nisin) than by HPCD alone. Regression coefficients (R²) and mean square error (MSE) were used to evaluate the model performance, indicating that the models could provide a good fitting to the experimental data.     

利用BP神经网络预测注水管道的腐蚀速率

利用人工神经网络的自适应、自组织学习能力 ,通过对训练样本集的学习 ,预测了注水管道的腐蚀速率。通过实例 ,采用 4种不同的预测腐蚀速率的方法 ,即采用传统的预测腐蚀速率的CVDA— 84规范、传统的BP神经网络、改进的Rumelhart和MBP神经网络计算注水管道的腐蚀速率。CVDA— 84规范偏保守 ,采用BP以及改进的BP神经网络预测的腐蚀速率和观测值基本一致。但采用BP人工神经网络预测时 ,迭代次数比CVDA大得多 ,采用改进的Rumel hart和MBP神经网络能有效地提高预测速度 ,改善网络的收敛性 ,并且使预测精度有所提高     

Effect of pomegranate powder on the heat inactivation of Escherichia coli O104:H4 in ground chicken

Health concerns have led to a search for natural plant-based antimicrobials. Ellagic acid has been shown to have antimicrobial activity against foodborne pathogens. The objective of this study was to assess the effect of a high-ellagic acid commercial pomegranate on the heat resistance of Escherichia coli O104:H4 in ground chicken. A full 2⁴ factorial design was used, consisting of temperature treatment with four levels (55.0, 57.5, 60.0, and 62.5 °C) and pomegranate with four levels (0.0, 1.0, 2.0, and 3.0 wt/wt. % containing 70% ellagic acid). Experiments were conducted twice, providing a total of 32 survival curves. A three-parameter Weibull primary model was used to describe survival kinetics. Secondary models were then developed to estimate the shape parameter β (i.e., curvature representing susceptibility of cells to stress), scale parameter γ (i.e., time to reach the first decimal reduction) and the 5.0-log lethality time t_5.0 (i.e., time to reach a 5.0-log reduction), all as polynomial functions of temperature and pomegranate powder concentration. The positive effect of pomegranate concentration on both β and γ demonstrated that the phenolic-rich pomegranate powder causes E. coli O104:H4 cells to become more susceptible to heat, increasing the steepness and concavity of the isothermal survival curves. It was estimated that the 5.0-log reduction time would reach a minimum at a pomegranate powder concentration of 1%, producing a 50% decrease in lethality time, in comparison to that without added pomegranate powder. Nonetheless, a mixed-effect omnibus regression further confirmed that the greatest difference in the thermal resistance of E. coli O104:H4 happened between tests with and without pomegranate powder. In fact, adding more than 1.0% pomegranate powder, at a constant temperature, resulted only in a marginal decrease in thermal resistance. Meat processors can use the model to design lethality treatments in order to achieve specific reductions of E. coli O104:H4 in ground chicken.     

Effect of organic acids,hydrogen peroxide and mild heat on inactivation of Escherichia coli O157:H7 on baby spinach

Minimally processed baby spinach contaminated with Escherichia coli O157:H7 has been associated with multiple outbreaks of foodborne illnesses recently. Chlorinated water is widely used to wash vegetables commercially, but this washing procedure has limited efficacy and can lead to the formation of carcinogenic substances. This study was conducted to determine the effects of organic acids and hydrogen peroxide alone and in binary combinations with or without mild heat (40 and 50 °C) on the inactivation of Escherichia coli O157:H7 on baby spinach. Baby spinach leaves were dip-inoculated with E. coli O157:H7 to a level of 6 log CFU/g and stored at 4 °C for 24 h before treatment. Individual washing solutions (1% and 2% lactic acid [LA], citric acid [CA], malic acid [MA], tartaric acid [TA], acetic acid [AA], hydrogen peroxide [H₂O₂] as well as binary combinations of LA, CA, MA and H₂O₂ at final concentrations of 1% were used to decontaminate spinach leaves at 22, 40 or 50 °C for 2–5 min to test their efficacy in reducing E. coli O157:H7. Chlorinated water (200 ppm free chlorine) decreased the population of E. coli O157:H7 on baby spinach by only 1.2–1.6 log CFU/g, which was not significantly different from DI water washing. Washing with 1% LA at 40 °C for 5 min was the most effective treatment achieving a 2.7 log reduction of E. coli O157:H7 which is significantly higher than chlorine washing. Washing with LA + CA or LA + HP at 40 °C for 5 min was equally effective against E. coli O157:H7, resulting in a 2.7 log reduction of E. coli O157:H7. The application of mild heat significantly enhanced the efficacy of washing solutions on the inactivation of E. coli O157:H7. There was, however, no significant difference between treatments at 40 °C for 5 min and 50 °C for 2 min. The results suggested that the use of organic acids in combination with mild heat can be a potential intervention to control E. coli O157:H7 on spinach.     

A risk assessment model for Escherichia coli O157:H7 in ground beef and beef cuts in Canada: Evaluating the effects of interventions

A stochastic, quantitative risk assessment model was developed to evaluate the public health risks associated with consumption of ground beef and beef cuts contaminated with Escherichia coli O157:H7 in Canada. The objectives of this work were to evaluate the relative effects of pre-harvest and processing interventions on public health risks using a novel approach, and compare the baseline risks from consumption of ground beef, non-intact beef cuts, and intact beef cuts. Rather than considering efficacy of all interventions at primary production and processing as default values, the model incorporated findings from critical systematic review and meta-analysis of published literature. Public health risks, expressed as average probability of illness per serving, were reduced by 30.9%–72.1%, 44.0%–96.5%, and 95.1%–99.9%, for single pre-harvest interventions, single processing interventions excluding water spray chilling, and combinations of interventions, respectively, relative to a worst-case scenario where no pre-harvest or processing interventions were applied. Combinations of interventions applied at pre-harvest and throughout processing resulted in the greatest relative risk reductions through their effects on both prevalence and concentration of the pathogen in cattle faeces and on cattle carcasses. The use of systematic review methodology to critically assess the results of scientific studies before use of the data in risk modelling enhances the confidence in risk predictions and provides a more evidenced-based model for public health analyses. Analysis of conditions reflective of current practices in Canada indicated that risks from consumption of ground beef were approximately two to three orders of magnitude greater than those for beef cuts, suggesting that risk management measures should focus on the former product to maximize benefits to public health. Risks from consumption of non-intact beef cuts, that is, steaks or roasts that are tenderized, were an order of magnitude greater than those for intact beef cuts. The model provides a useful tool to compare relative efficacies of different intervention strategies to determine their potential impact on public health risks. This tool can be used to evaluate an essentially limitless combination of intervention scenarios and can be adapted to include interventions applied at different points along the farm-to-fork continuum as critically-reviewed data become available.     

Inactivation of Escherichia coli O157:H7 during cooking of non-intact beef treated with tenderization/marination and flavoring ingredients

This study examined the effect of tenderizing/marinating and flavoring ingredients on thermal inactivation of Escherichia coli O157:H7 in a lean ground beef model system, simulating non-intact products. Ground beef (3% fat) was inoculated with E. coli O157:H7 (5 strains; 6–7 log CFU/g), followed by mixing with nothing (control) or solutions of water, a mixture of flavoring agents (FA), 0.23% calcium chloride (CC) + FA, CC + FA + 0.3% acetic acid (AA), 0.5% sodium chloride (NaCl) + 0.25% sodium tripolyphosphate (STP), NaCl + STP + FA, NaCl + STP + 1.8% potassium lactate (PL), NaCl + STP + PL + FA, NaCl + STP + PL + AA, and NaCl + STP + PL + AA + FA. Samples (30 g) were extruded into tubes, stored (4 °C) overnight, and cooked to 60 °C (rare) or 65 °C (medium-rare) in a water bath. Cooking weight losses, and fat and moisture contents, water activity, pH, and total bacterial and E. coli O157:H7 populations were determined after inoculation, after storage, and after heating. Reductions of the pathogen at 60 °C in acid (AA)-treated samples were higher than reductions obtained in samples not treated with acid. Surviving pathogen counts at 65 °C in NaCl and STP-treated samples with no acid were higher (P < 0.05) than those of samples of all other tested treatments; however, the counts decreased to 0.7–1.6 log CFU/g when AA was added. Overall, the results of the study indicate that tenderizing/flavoring ingredient formulations combined with 0.3% AA (i.e., CC + FA + AA, NaCl + STP + PL + AA, and NaCl + STP + PL + AA + FA) enhanced destruction of E. coli O157:H7 during cooking of a non-intact beef product.     

BP人工神经网络在济阳拗陷圈闭地质评价中的应用

人工神经网络圈闭地质评价方法可以充分考虑不同勘探程度，不同地质情况、不同用户要求，并且根据专家的意见和具体参数特点，灵活设置权值大小，使圈闭地质评价达到客观反映和主观评价的统一。本文应用人工神经网络方法，在济阳拗陷建立四大类20多种不同类型的典型样本圈闭，通过统计分析确定各种类型典型样本圈闭不同地质因素的权重，并对50个圈闭进行了地质评价。在20个已钻圈闭中，有18个圈闭的预测结果与实钻结果相符，吻合率达90％；在10个未钻圈闭中，有6个圈闭的评价较好，具有较高的勘探价值。     

Evaluation of a novel antimicrobial solution and its potential for control Escherichia coli O157:H7, non-O157:H7 shiga toxin-producing E. coli,Salmonella spp., and Listeria monocytogenes on beef

The goal of this study was to evaluate the efficacy of a novel antimicrobial solution made with chitosan, lauric arginate ester, and organic acids on Escherichia coli O157:H7, Salmonella spp., Listeria monocytogenes, and non-O157 shiga toxin-producing E. coli cocktails and to test its potential to be used as a marinade for raw beef. Fresh beef top round steaks were surface-inoculated with the pathogen cocktails at approximately 2.5 or 4.5 Log CFU/cm², marinated with the antimicrobial solution (AMS), and then stored at 4 °C for 6, 24, and 48 h. Three commercially available marinades were used for comparison. Results revealed that AMS had the most antimicrobial effect regardless of the type or inoculation level of pathogens (P < 0.05). After 6 h, the AMS marination reduced all pathogens to levels below the limit of detection (<1 Log CFU/cm²), resulting in a 3.5 Log CFU/cm² reduction. When AMS was diluted with autoclaved distilled water by 5 times (AMS 1:5) or 10 times (AMS 1:10), its antimicrobial efficacy was impacted by marination time, the inoculated pathogens, and the inoculation levels. This study demonstrates that the developed antimicrobial solution has a great potential to be used during marination by consumers to ensure better food safety.     

Combination of bioprotective cultures with EDTA to reduce Escherichia coli O157:H7 in frozen ground-beef patties

The effectiveness of bacteriocin-producing Lactobacillus curvatus CRL705 and Lactococcus lactis CRL1109 in combination with Na₂EDTA on frozen ground-beef patties contaminated with Escherichia coli O157:H7, was investigated under temperature abuse conditions (5 °C during 9 days). The presence of the bioprotective cultures (ca. 10⁷ CFU/g) and chelator (48 mM) resulted in one log CFU/g reduction for E. coli strain, compared to the control on day 0. Similarly, a significant decline for indigenous coliforms in ground-beef patties was also observed in the presence of bacteriocinogenic strains and chelator. However, in the absence of Na₂EDTA, neither E. coli nor coliforms were inhibited by the bioprotective cultures, the pathogen reaching similar counts than control samples (5.22 and 3.60 log CFU/g, respectively) at 9 days. When the growth of bacteriocinogenic strains on patties was evaluated, they were able to increase their population producing bacteriocins after 48 h up to the end of incubation period while a near neutral pH in the presence of Na₂EDTA was detected. Non substantial effect on of ground-beef patties color was produced in the presence of bioprotective cultures, while a darker color developed in those added with the chelator. The simultaneous treatment with bioprotective cultures and Na₂EDTA may be of value for the control of E. coli O157:H7 in temperature abused ground-beef patties.     

Development of an immunomagnetic separation method for efficient enrichment of Escherichia coli O157:H7

Immunomagnetic separation uses antibody-coated paramagnetic particles to selectively bind and purify the target organisms from a comprehensive range of complex food matrices. Aim of this study was to develop and optimize an immunomagnetic separation method based on monoclonal antibody for efficient isolation of Escherichia coli O157:H7 in food samples. The key parameters for preparing the immunomagnetic beads; the coupling rate between monoclonal antibody and magnetic beads, additive amount of immunomagnetic beads, and magnetic separation times were optimized with different concentrations of E. coli O157:H7. Under optimized conditions, the capture efficiency (CE) was greater than 98% against 10¹–10⁶ cells of E. coli O157:H7 with 0.05 mg immunomagnetic beads. The immunomagnetic beads exhibited high specific binding with E. coli O157:H7 strains (CE > 98%), and low binding with non-target bacteria (CE < 2%) except for S. aureus (CE = 23.6%). The capture efficiency of immunomagnetic beads against E. coli O157:H7 in ground beef and milk samples were 94.4% and 99.8%, respectively.     

Sublethal injury and recovery of Escherichia coli O157:H7 by high pressure carbon dioxide

A study was carried out to investigate possible sublethal injury caused by high pressure carbon dioxide (HPCD) to Escherichia coli O157:H7 suspended in phosphate-buffered saline (PBS, pH 7.00). The treatment pressure was 5 MPa, treatment temperatures were 25–37 °C and treatment time was 5–70 min. Only 1.21 log₁₀ cycles reduction was obtained in the nonselective medium, while a higher reduction of 5.18 log₁₀ cycles was obtained in the selective medium after treatment at 5 MPa and 25 °C for 50 min, indicating HPCD could induce sublethal injury of E. coli cells and these cells could not recover in the selective medium. The proportion of the sublethally injured E. coli cells in the survivors increased dramatically up to 72.4% with increasing the treatment time from 20 min to 30 min by HPCD at 5 MPa and 25 °C, and this proportion increased gradually with increasing the treatment time, up to 100% at 5 MPa and 25 °C for 60 min. The effect of recovery media, inhibitors of specific metabolic processes, Mg and Ca cations on the recovery of the sublethally injured cells was also investigated. When PBS, peptone water, tryptic soy broth (TSB) and carrot juice were used as recovery media, the maximum repair rate of the sublethally injured cells was found in TSB and the minimum was in PBS. The addition of inhibitors such as sodium azide, chloramphenicol, rifampicin and penicillin G showed that repair of most sublethally injured cells required energy, protein and RNA synthesis, but was not dependent on peptidoglycan synthesis. Moreover, Mg and Ca cations were also needed in the repair.     

应用神经网络模式识别技术进行测井沉积学研究

将人工神经网络(ANN)模式识别技术应用于测井沉积学解释中，可以实现井剖面沉积环境的连续自动解释，大大提高解释精度和工作效率。在确定济阳坳陷车镇凹陷关键井8种主要沉积相及测井响应模式的基础上，从测井曲线中提取出10种具有较明确地质意义的特征参数，在岩心观察以及地区经验的基础上优选指示沉积相灵敏性较好的曲线组合，基于神经网络模式识别技术进行井剖面沉积微相自动解释。采用自行开发的软件解释了40余口井的沉积微相，取得了较好的效果。该软件适用于具有一定区域背景知识和地质解释经验的人员。图3表2参16     

Efficacy of near neutral and alkaline pH electrolyzed oxidizing waters to control Escherichia coli O157:H7 and Salmonella Typhimurium DT 104 from beef hides

In this study efficacy of near neutral and alkaline pH electrolyzed oxidizing waters to reduce aerobic plate counts (AC) and Enterobacteriaceae (EC) from uninoculated fresh cattle hides and Escherichia coli O157:H7 and Salmonella Typhimurium DT 104 from inoculated hides were determined. Fresh hides were cut in to 15 by 20 cm pieces and subjected to a total of eight different treatment solutions; near neutral pH EO water (NEW-pH 6.5 at room temperature, 150 mg/L available chlorine), alkaline pH EO water (AEO-pH 11.6 at room temperature), hot alkaline pH EO water at 43 °C (HAEO-pH 11.60), alkaline pH EO water spray followed by 150 mg/L available chlorine containing near neutral pH EO water spray (A-NEW-both at room temperature), Blitz™ (PAA, pH 3.02 at room temperature), 5% lactic acid (LA, pH 2.04 at room temperature), deionized water (W) and no treatment (Control). For each treatment, 60 ml treatment solution was sprayed on hide using a hand held sprayer. Similar treatment protocol was employed to treat hide pieces inoculated with E. coli O157:H7 and S. Typhimurium DT 104. Five percent lactic acid spray treatment was found to be the most effective treatment and achieved 2.77, 2.74, 2.75 and 2.98 log CFU/cm² of AC, EC, E. coli O157:H7 and S. Typhimurium DT 104 reductions, respectively. All EO water treatments were equally effective in reducing all target microorganisms, except E. coli O157:H7. HAEO and A-NEW treatments yielded significant reduction of E. coli O157:H7 compared to other EO water treatments. These results indicate that various EO water treatments could become viable options to reduce pathogens on hide during slaughter.     

Sublethal injury and recovery of Escherichia coli O157:H7 and K-12 after exposure to lactic acid

Lactic acid can induce sublethal injury of Escherichia coli. When conditions become favorable, injured E. coli can recover physiological function and fully virulence, which is a great concern in the field of food safety. The injury and recovery of E. coli O157:H7 and K-12 by lactic acid were investigated in this study. Sublethally injured E. coli cells widely persisted after a 60-min exposure to lactic acid with different pH values (E. coli O157:H7: pH 3.0–4.6, E. coli K-12: pH 3.4–5.0). The sublethally injured ratio of E. coli O157:H7 and K-12 by lactic acid decreased as incubation temperature decreasing. Both sublethally injured E. coli O157:H7 and K-12 induced by lactic acid could be completely recovered in trypticase soy broth at 37 °C within 60 min. For both E. coli O157:H7 and K-12, sodium pyruvate, Tween 80, or certain cations (Mn, Fe, or Zn) could significantly increase the recovery ratio. The recovery ratios of injured E. coli K-12 and O157:H7 were only 74.2% and 92.6% after 80 min incubation in minA, respectively. But they can both be completely recovered within 80 min in minA with sodium pyruvate, with Tween 80, or with cations (Mn, Fe, or Zn). But Mg and Ca cations did not affect the recovery time. The understanding of injury and recovery of E. coli could contribute to develop effective decontaminating treatment by lactic acid, and develop techniques for detecting sublethally injured E. coli cells.