Modeling of Free Chlorine Consumption and Escherichia coli O157:H7 Cross‐Contamination During Fresh‐Cut Produce Wash Cycles

Controlling the free chlorine (FC) availability in wash water during sanitization of fresh produce enhances our ability to reduce microbial levels and prevent cross‐contamination. However, maintaining an ideal concentration of FC that could prevent the risk of contamination within the wash system is still a technical challenge in the industry, indicating the need to better understand wash water chemistry dynamics. Using bench‐scale experiments and modeling approaches, we developed a comprehensive mathematical model to predict the FC concentration during fresh‐cut produce wash processes for different lettuce types (romaine, iceberg, green leaf, and red leaf), carrots, and green cabbage as well as Escherichia coli O157:H7 cross‐contamination during fresh‐cut iceberg lettuce washing. Fresh‐cut produce exudates, as measured by chemical oxygen demand (COD) levels, appear to be the primary source of consumption of FC in wash water, with an apparent reaction rate ranging from L/mg·min for all produce types tested, at stable pH levels (6.5 to 7.0) in the wash water. COD levels increased over time as more produce was washed and the lettuce type impacted the rate of increase in organic load. The model parameters from our experimental data were compared to those obtained from a pilot‐plant scale study for lettuce, and similar reaction rate constant (5.38 × 10^-4 L/mg·min) was noted, supporting our hypothesis that rise in COD is the main cause of consumption of FC levels in the wash water. We also identified that the bacterial transfer mechanism described by our model is robust relative to experimental scale and pathogen levels in the wash water. Finally, we proposed functions that quantify an upper bound on pathogen levels in the water and on cross‐contaminated lettuce, indicating the maximum potential of water‐mediated cross‐contamination. Our model results could help indicate the limits of FC control to prevent cross‐contamination during lettuce washing.     

Escherichia coli O157:H7 facilitates the penetration of Staphylococcus aureus into table eggs

Abstract: Fresh eggshells collected from a local farm were subjected to different levels of surface contamination with feces containing different levels (3 to 5 log₁₀) of Escherichia coli O157:H7 or Staphylococcus aureus and incubated at 3 different temperatures (10, 25, and 32 °C). The penetration rates of contaminating bacteria were followed throughout the incubation period by tracing bacterial presence in shell, shell membranes, albumen, and yolk. The study revealed the ability of both E. coli O157:H7 and enterotoxigenic S. aureus to grow on shell in feces, penetrate the shell, and move and multiply within egg contents at different rates and periods depending on bacterial type and incubation conditions. High temperatures (25 and 32 °C) increased penetration rate, whereas storage at 10 °C decreased significantly the rate of penetration. High levels of contamination with E. coli O157:H7 also shortened the time needed for the penetration process. Results showed that when eggshells were contaminated with both organisms simultaneously, the penetration of E. coli O157:H7 preceded that of S. aureus and facilitated the invasion of the latter bacteria.     

Effect of irradiation temperature on inactivation of Escherichia coli O157:H7 and Staphylococcus aureus

The resistance of Escherichia coli O157:H7 and Staphylococcus aureus in ground beef to gamma radiation was significantly (P < 0.05) higher at subfreezing temperatures than above freezing. Ground beef was inoculated (ca. 2 x 10(8) CFU/g) with five isolates of either E. coli O157:H7 or S. aureus and subdivided into 25-g samples, vacuum packaged in barrier pouches, and tempered to 20, 12, 4, 0, -4, -12, -20, -30, -40, or -76 degrees C before gamma irradiation. The studies were repeated twice. The D10-values for both of these pathogens increased significantly at subfreezing temperatures, reaching maxima at approximately -20 degrees C. The D10-values for E. coli O157:H7 at 4 and -20 degrees C were 0.39 +/- 0.04 and 0.98 +/- 0.23 kGy, respectively. The D10-values for S. aureus at 0 and -20 degrees C were 0.51 degrees 0.02 and 0.88 +/- 0.05 kGy, respectively.     

适配体结合量子点技术同时检测金黄色葡萄球菌和大肠埃希氏菌O157:H7方法

目的：基于适配体结合量子点技术,建立一种同时针对金黄色葡萄球菌、大肠埃希氏菌O157:H7两种食源性致病菌快速高效、灵敏的检测方法。方法：利用表面增强拉曼光谱技术筛选出与目标菌结合特异性较好的2?种适配体;利用免疫磁珠与适配体偶联技术特异性捕获2?种目标菌;选取不同发光原理的2?种量子点,并结合量子点荧光标记技术构建“磁珠＋目标菌＋量子点”的“三明治结构”,通过对结构条件优化确定2?种目标菌的检出限,并应用到市售无菌牛乳实际样品中进行加标回收率实验。结果：本研究证明所选取的2?条适配体与目标菌的结合具有高特异性,可实现对2?种目标菌的同时检测。对“三明治结构”优化结果表明：2?种目标菌的最佳捕获条件为免疫捕获时间45?min、磁分离时间2?min;适配体最适浓度为400?nmol/L;金黄色葡萄球菌检出限为101?CFU/mL,线性方程为Y=28.51X＋126.67（R2=0.973）;大肠埃希氏菌O157:H7检出限均为102?CFU/mL,线性方程为Y=92.86X－64.67（R2=0.987）,其中,Y为荧光强度,X为细菌菌落数的对数值,拟合度良好。且在牛乳样品中金黄色葡萄球菌和大肠埃希氏菌O157:H7回收率分别为94.6%～102.8%和93.4%～100.4%。结论：本研究所建立的方法能够实现同时对2?种食源性致病菌快速、高效检测,该方法易操作且灵敏度高,在食品加工生产安全检测方面具有良好的应用前景。     

三重荧光PCR检测沙门氏菌、金黄色葡萄球菌和大肠埃希氏菌O157:H7

目的 建立一种检验沙门氏菌、金黄色葡萄球菌、大肠埃希氏菌O157:H7的TaqMan探针三重荧光PCR方法.方法 针对沙门氏菌属特异性invA基因、金黄色葡萄球菌rpoB基因、大肠埃希氏菌O157:H7的rfbE基因设计引物与探针,建立三重荧光PCR体系,对引物与探针浓度及退火温度优化,并进行特异性和敏感性研究.结果 ...     

Decontamination of Salmonella,Shigella, and Escherichia coli O157:H7 from Leafy Green Vegetables Using Edible Plant Extracts

Fresh cilantro, parsley, and spinach are products that are regularly consumed fresh, but are difficult to decontaminate, as a result, they are common vehicles of transmission of enteropathogenic bacteria. In this study, the efficacy of plant extracts as alternatives for disinfection of cilantro, parsley, and spinach that were artificially contaminated with Salmonella, Escherichia coli O157:H7, and Shigella sonnei was determined. Edible plant extracts obtained using ethanol as the extraction solvent were tested to determine the minimum bactericidal concentration (MBC) and those that exhibited the lowest MBC were selected for further studies. Leaves of fresh greens were washed with sterile water and dried. For seeding, leaves were submerged in suspensions of 2 different concentrations of bacteria (1.5 × 10⁸ and 1 × 10⁵), dried, and then stored at 4 °C until use. To determine the effects of the extracts, inoculated leafy greens were submerged in a container and subjected to treatments with chlorine, Citrol®, or selected plant extracts. Each treatment type was stored at 4 °C for 0, 1, 5, and 7 d, and the bacterial counts were determined. From the 41 plant extracts tested, the extracts from oregano leaves and from the peel and pulp of limes were found to be as effective as chlorine or Citrol® in reducing by > 2 logs, the population of pathogenic bacteria on leafy greens and therefore, may be a natural and edible alternative to chemicals to reduce the risk of Salmonella, E. coli O157:H7 and S. sonnei contamination on leafy vegetables. Practical Application: The antimicrobial efficacy of the extracts of Mexican lime and oregano was clearly demonstrated on cilantro, parsley, and spinach. The extracts of Mexican lime and oregano provide alternatives to chlorine to significantly reduce bacterial pathogens that have been associated with outbreaks from contaminated leafy green vegetables. A simple, low cost, and labor‐saving extraction system for production of the extracts was used.     

Physiological changes of Escherichia coli O157:H7 and Staphylococcus aureus following exposure to high hydrostatic pressure

Morphological changes and membrane integrity of Escherichia coli O157:H7 and Staphylococcus aureus cells before and after high hydrostatic pressure (HHP) treatments (200–400 MPa) and time (1–5 min), at a constant temperature (40 °C), in peptone water were examined by using scanning electron microscopy (SEM) and fluorescent microscopy, respectively. SEM images showed that unpressurized cells exhibited a smooth surface appearance. E. coli O157:H7 cells exposed to pressure treatments first appeared larger, then with increasing pressure distorted with dimples and pinches. In case of S. aureus, the cells pressurized at low pressure levels did not show any significant change. The surface appearance became rough and cracked when the cells were exposed to higher pressure levels. Images of fluorescent microscopy showed that a small proportion of bacterial cells were not green fluorescent at lower pressure levels. The other part of the cell population was red fluorescent representing dead cells and the number of red fluorescent cells increased with increasing pressure. The cells with a yellowish color showed that varying levels of membrane damage occurred under HHP. The combinations of mild heat, antimicrobial substances and HHP treatment can be used to inactivate food borne pathogens of varying pressure resistance in the food industry for safe processing conditions. However, the resultant damaged cells at different levels should be taken into account during storage to prevent their recovery.     

Antimicrobial Effect of Sour Pomegranate Sauce on Escherichia coli O157 : H7 and Staphylococcus aureus

Pomegranate sauce is one of the most popular pomegranate products produced in Turkey. This study was conducted to determine the minimum inhibitory concentrations (MICs) of both traditional and commercial sour pomegranate sauce samples on Staphylococcus aureus (ATCC 25923) and Escherichia coli O157 : H7 (ATCC 43895). The initial microflora of the pomegranate sauce samples was determined by performing the enumerations of total aerobic mesophilic bacteria, yeast and mold, S. aureus, E. coli, and the determination of Salmonella spp. MIC tests were applied to the neutralized and the original (unneutralized) sour pomegranate sauce samples in order to put forth the inhibition effect depending on low pH value. It was found that inhibitory effect of the traditional and the commercial samples, except one sample, on pathogens was not only due to the acidity of the products. The results of MIC tests indicated that although both traditional and commercial samples showed a considerable inhibitory effect on test microorganisms, the traditional pomegranate sauce samples were more effective than the commercial ones.