Occurrence of Escherichia coli O157:H7 and other enterohemorrhagic Escherichia coli in the environment

Enterohemorrhagic Escherichia coli (EHEC) (O157 and other serotypes) are zoonotic pathogens linked with severe human illnesses. The main virulence factors of EHEC are the Shiga toxins, among others. Most of the genes coding for these toxins are bacteriophage-encoded. Although ruminants are recognized as their main natural reservoir, water has also been documented as a way of transmission of EHEC. E. coli O157:H7 and other EHEC may contaminate waters (recreational, drinking or irrigation waters) through feces from humans and other animals. Indeed, the occurrence of EHEC carrying the stx2 gene in raw municipal sewage and animal wastewater from several origins has been widely documented. However, the evaluation of the persistence of naturally occurring EHEC in the environment is still difficult due to methodological problems. Methods proposed for the detection and isolation of stx-encoding bacteria, ranging from the classic culture-based methods to molecular approaches, and their application in the environment, are discussed here. Most virulence factors associated with these strains are linked to either plasmids or phages, and consequently they are likely to be subject to horizontal gene transfer between species or serotypes. Moreover, the presence of infectious stx-phages isolated as free particles in the environment and their high persistence in water systems suggest that they may contribute to the spread of stx genes, as they are directly involved in the emergence of new pathogenic strains, which might have important health consequences.     

Survival and growth of Listeria monocytogenes and enterohemorrhagic Escherichia coli O157:H7 in minimally processed artichokes

The ability of Listeria monocytogenes and Escherichia coli O157:H7 inoculated by immersion (at 4.6 and 5.5 log CFU/ g, respectively) to survive on artichokes during various stages of preparation was determined. Peeling, cutting, and disinfecting operations (immersion in 50 ppm of a free chlorine solution at 4 degrees C for 5 min) reduced populations of L. monocytogenes and E. coli O157:H7 by only 1.6 and 0.8 log units, respectively. An organic acid rinse (0.02% citric acid and 0.2% ascorbic acid) was more effective than a tap water rinse in removing these pathogens. Given the possibility of both pathogens being present on artichokes at the packaging stage, their behavior during the storage of minimally processed artichokes was investigated. For this purpose, batches of artichokes inoculated with L. monocytogenes or E. coli O157:H7 (at 5.5 and 5.2 log CFU/g, respectively) were packaged in P-Plus film bags and stored at 4 degrees C for 16 days. During this period, the equilibrium atmosphere composition and natural background microflora (mesophiles, psychrotrophs, anaerobes, and fecal coliforms) were also analyzed. For the two studied pathogens, the inoculum did not have any effect on the final atmospheric composition (10% O2, 13% CO2) or on the survival of the natural background microflora of the artichokes. L. monocytogenes was able to survive during the entire storage period in the inoculated batches, while the E. coli O157:H7 level increased by 1.5 log units in the inoculated batch during the storage period. The modified atmosphere was unable to control the behavior of either pathogen.     

大肠杆菌O157:H7的冷冻损伤及解冻存活

为探讨冷冻后残存的大肠杆菌O157:H7（Escherichia coli O157:H7）在解冻后的存活情况,本研究首先比较4 株E. coli O157:H7冷冻后的死亡和损伤情况,进而采用无营养的磷酸盐缓冲液作为基质研究冷冻后不同解冻方式对E. coli O157:H7存活的影响。结果表明：4 株E. coli O157:H7 －20 ℃冷冻24、48、72 h后均发生了一定程度的死亡和损伤,冷冻时间越长细菌致死和致伤程度越明显,且存在菌株差异,冷冻72?h时菌株CICC21530的损伤率最高,为87.70%。采用混合菌株进行解冻实验,4?株E.?coli?O157:H7磷酸盐缓冲液菌液冷冻后立即置于20、30、37?℃解冻,细菌发生了进一步的死亡,解冻温度越高死亡越明显,3?个温度组在解冻48?h时菌落数均显著低于冷冻72?h时菌落数（P＜0.05）。进一步探讨缓慢解冻方式对菌体存活的影响,菌液冷冻后先置于4?℃一定时间（0、2、6、12?h）,再置于37?℃不同时间（5、10、30?min）观察菌株存活情况,结果表明4?℃缓慢解冻时间越长,越有利于细菌的存活,4?℃、12?h/37?℃、5～30?min解冻方式下改良山梨醇麦康凯琼脂上菌落数仍显著低于胰蛋白胨大豆琼脂上的菌落数（P＜0.05）,表明仍有损伤菌的存在。本实验提示采用缓慢解冻反而有利于残存菌的存活,冷冻食品风险评估时应重视残存菌尤其是损伤菌的检测和控制。     

Survival of Salmonella and Escherichia coli O157:H7 in chorizos

Mexican-style raw meat sausages (chorizos) are not regulated in California when they are produced in small ethnic food markets. These sausages are sold uncooked, but their formulation imparts a color that may lead the consumer to assume that they are already cooked, and thus the chorizos may sometimes be eaten without proper cooking. If pathogens are present in such cases, illness may result. Survival of Salmonella and Escherichia coli O157:H7 in chorizos was evaluated under different storage conditions selected based on an initial survey of uninspected chorizos in California. Chorizos were formulated with five different initial water activity (aw) values (0.85, 0.90, 0.93, 0.95, and 0.97), stored under four conditions (refrigeration at 6 to 8 degrees C, room temperature at 24 to 26 degrees C, under a hood at 24 to 26 degrees C with forced air circulation, and incubation at 30 to 31 degrees C with convective air circulation), and sampled after 1, 2, 4, and 7 days. The initial pH was 4.8 and remained near 5.0 from day 1 of the sampling period. Two separate studies of packs inoculated with five-strain cocktails of Salmonella and of E. coli O157:H7 were performed twice for each initial aw. The three lowest aw values (0.85, 0.90, and 0.93) and the incubation and hood storage conditions were more effective (P < or = 0.05) at reducing the target pathogen levels in chorizos than were the two highest aw values (0.95 and 0.97) and the refrigeration storage condition, regardless of storage time. These results provide a scientific basis for guidelines given to producers of uninspected chorizo and should reduce the probability of foodborne illness associated with these products.     

Survival of Escherichia coli O157:H7 in cucumber fermentation brines

Abstract: Bacterial pathogens have been reported on fresh cucumbers and other vegetables used for commercial fermentation. The Food and Drug Administration currently has a 5‐log reduction standard for E. coli O157:H7 and other vegetative pathogens in acidified pickle products. For fermented vegetables, which are acid foods, there is little data documenting the conditions needed to kill acid resistant pathogens. To address this knowledge gap, we obtained 10 different cucumber fermentation brines at different stages of fermentation from 5 domestic commercial plants. Cucumber brines were used to represent vegetable fermentations because cabbage and other vegetables may have inhibitory compounds that may affect survival. The 5‐log reduction times for E. coli O157:H7 strains in the commercial brines were found to be positively correlated with brine pH, and ranged from 3 to 24 d for pH values of 3.2 to 4.6, respectively. In a laboratory cucumber juice medium that had been previously fermented with Lactobacillus plantarum or Leuconostoc mesenteroides (pH 3.9), a 5‐log reduction was achieved within 1 to 16 d depending on pH, acid concentration, and temperature. During competitive growth at 30 °C in the presence of L. plantarum or L. mesenteroides in cucumber juice, E. coli O157:H7 cell numbers were reduced to below the level of detection within 2 to 3 d. These data may be used to aid manufacturers of fermented vegetable products determine safe production practices based on fermentation pH and temperature. Practical Application: Disease causing strains of the bacterium E. coli may be present on fresh vegetables. Our investigation determined the time needed to kill E. coli in cucumber fermentation brines and how E. coli strains are killed in competition with naturally present lactic acid bacteria. Our results showed how brine pH and other brine conditions affected the killing of E. coli strains. These data can be used by producers of fermented vegetable products to help assure consumer safety.     

可视化-环介导等温扩增技术检测肠出血性大肠杆菌O157:H7

目的 建立可视化的环介导等温扩增技术(loop-mediated isothermal amplification, LAMP)联合横向流动试纸条(lateral flow dipstick, LFD)方法检测肠出血性大肠杆菌(enterohemorrhagic Escherichia coli, EHEC)O157:H7的分析方法。方法 以EHEC O157:H7的遗传标志性基因z3276基因序列为检测靶标设计6条LAMP特异性引物, 其中2条环引物分别标记异硫氰酸荧光素和地高辛, 用LFD检测扩增产物, 建立EHEC O157:H7 LAMP-LFD检测方法。结果 所建立的检测方法能够特异性的检测EHEC O157:H7, 与试验对照菌株EHEC O26、O145、O45、O121, 及其他主要大肠杆菌血清型O25、O78、O103、O111、O127、O138、O139、O141, 及禽致病性大肠杆菌(avian pathogenic Escherichia coli, APEC)E058、肠致病性大肠杆菌(enteropathogenic Escherichia coli, EPEC)SEC627、EPEC SEC689、K12-MG1655、BL21, 和其他种属的受试菌, 不存在交叉反应; 对EHEC O157:H7纯培养物的最低检测限为1.3 CFU/mL。结论 本研究所建立的LAMP-LFD检测方法特异性和敏感性良好, 操作简单, 结果可视。     

肠出血性大肠杆菌O157:H7的分子生物学检测及PCR检测

大肠杆菌一些特殊的血清型具有致病性,肠出血性大肠杆菌是大肠杆菌的一个亚型,主要致病菌株为O157:H7,可引起感染性腹泻,因能引起人类的出血性肠炎而得名。本文综述了分子生物学检测肠出血性大肠杆菌O157:H7的研究进展。分子生物学检测是利用抗原抗体特异性结合反应检测各种物质的分析方法,主要包括酶联免疫吸附法(ELISA)、胶体免疫金层析法以及免疫磁珠分离法(IMS)。PCR技术检测肠出血性大肠杆菌O157:H7,主要包括常规PCR检测、多重PCR检测以及实时荧光定量PCR检测。这两种方法灵敏度高、特异性强、操作简便、结果准确等优点,是检测肠出血性大肠杆菌O157:H7的常用方法。     

Transmission electron microscopy study of enterohemorrhagic Escherichia coli O157:H7 in apple tissue

We investigated the ability of enterohemorrhagic Escherichia coli O157:H7 to spread in wounded apple tissue by transmission electron microscopy. Red Delicious apples were wounded with an artist knife (7 mm depth) and either inoculated with 10 microl per wound of decimally diluted E. coli O157:H7 or submerged into E. coli O157:H7 suspended in sterile distilled water and then stored at 37 degrees C for 24 h. Transmission electron microscopy showed E. coli O157:H7 formed bacterial aggregates near the apple cell walls, and single cells were in close proximity to the apple cell wall surfaces and to plasma membranes. E. coli O157:H7 presence caused degradation of plasma membranes and release of the cytoplasm contents of the apple cortical cells into the central vacuole. Apple tissue turgor pressure tests showed that the apple cells infected with E. coli O157:H7 isolates were more likely to rupture than the control noninoculated apple cells. E. coli O157:H7 cells grown in apple tissue showed the formation of granules and vesicles within the bacterial cytoplasma and separation of the plasma membranes. Our study shows that E. coli O157:H7 can grow and survive in the apple tissue environment by causing degradation of the apple cellular components.     

Survival of Escherichia coli O157:H7 in traditional African yoghurt fermentation

Growth and survival of a nontoxigenic strain of Escherichia coli O157:H7 (ATCC 43888) was determined in traditionally fermented pasteurized milk. Preheated milk was inoculated with 1% (v/v) of a mixed culture of Lactobacillus delbrueckii ssp. bulgaricus (NCIMB 11778) and Streptococcus salivarius ssp. thermophilus (NCIMB 110368) and incubated at 25, 30, 37 or 43 degrees C for 24 h. E. coli O157:H7 (10(5) CFU/ml) were introduced into the milk pre- and post-fermentation. Fermented milk samples were subsequently stored at either 4 degrees C (refrigerator temperature) or 25 degrees C (to mimic African ambient temperature) for 5 days. After 24 h of fermentation, the pH of the samples fermented at the higher temperatures of 37-43 degrees C decreased from 6.8 to 4.4-4.0 ( +/- 0.2) whereas at the lower temperature of 25 degrees C, the pH decreased to pH 5.0 +/- 0.1. During this period, viable counts for E. coli O157:H7 increased from 10(5) to 10(8) - 10(9) CFU/ml except in milk fermented at 43 degrees C wherein viability declined to 10(4) CFU/ml. In fermented (25-30 degrees C) milk stored at 4 degrees C for 5 days, E. coli O157:H7 viability decreased from 10(8-9) to 10(6-7) CFU/ml whereas milk fermented at 43 degrees C resulted in loss of detectable cells. In contrast, storage of fermented milk samples at 25 degrees C for 5 days eventually resulted in complete loss of viability irrespective of fermentation temperature. Stationary phase E. coli O157:H7 inoculated post-fermentation (25 and 43 degrees C) survived during 4 degrees C storage, but not 25 degrees C storage. Fermentation temperature and subsequent storage temperature are critical to the growth and survival of E. coli O157:H7 in traditional fermented products involving yoghurt starter cultures.     

Isolation and characterization of Escherichia coli O157:H7 from retail meats in Argentina

Between February and May 2000, 279 meat samples were collected from 136 retail stores in Gualeguaychú City, Argentina. Samples were assayed for Escherichia coli O157:H7 by selective enrichment in modified EC broth containing novobiocin, followed by immunomagnetic separation (IMS) and plating onto both sorbitol MacConkey agar supplemented with cefixime and potassium tellurite and a chromogenic medium. Eleven E. coli O157:H7 isolates were detected in 6 (3.8%) of 160 ground beef samples, in 4 (4.8%) of 83 fresh sausages, and in 1 (3.3%) of 30 dry sausages. E. coli O157:H7 was not isolated from five hamburger patties or one barbecue-type fresh sausage assayed. The isolates were tested for virulence-related genes. Ten additional Shiga toxin-producing E. coli (STEC) O157:H7 isolates of food origin, recovered from different locations in Argentina, were included for comparison purposes. All 21 isolates harbored both eae and EHEC-hlyA genes, and 12 (57.1%) encoded stx2/stx2vh-a. The isolates were of phage types 87 (seven strains), 14 (four strains), 4 (three strains), and 26 (one strain). Six strains were nontypable by phage typing. Pulsed-field gel electrophoresis (PFGE) revealed 19 XbaI-PFGE profiles. Fifteen (71%) strains were grouped in four clusters, which shared more than 80% of DNA restriction fragments. The enrichment culture method with IMS was a sensitive procedure to detect E. coli O157:H7 strains in retail meats. Some of the isolates from different stores presented a high clonal relatedness, as determined by XhaI-PFGE and phage typing, and harbored the virulence factors associated with human illness.     

Efficacy of allyl isothiocyanate in killing enterohemorrhagic Escherichia coli O157:H7 on alfalfa seeds

Volatile compounds occurring in the essential oil of plants were tested for their efficacy in killing Escherichia coli O157:H7. Experiments using an agar disk assay revealed that exposure of the pathogen to 50 microl of eugenol, carvacrol, linalool, or methyl jasmonate in a 950-cc jar at 20, 37 or 47 degrees C for up to 48 h failed to inhibit colony formation. However, exposure to 8 microl of allyl isothiocyanate (AIT) (equivalent to 8.4 ppm in the air within the jar, if completely volatilized) resulted in more than a 7-log10 reduction in population of E. coli O157:H7 at 37 degrees C within 48 h; significant (P < or = 0.05) reduction in populations also occurred in the presence of 4 microl of AIT compared to 2 microl, which had no lethal affect. At 20 degrees C, the lethality of AIT was substantially less, although significant reduction occurred when disks were exposed to 8 or 10 microl of AIT compared to 4 or 6 microl and when exposed to 4 or 6 microl compared to 2 microl. Treatment with 10 microl of AIT for 5 h at 47 degrees C resulted in death of 6 log10 of E. coli O157:H7. The efficacy of AIT in killing E. coli O157:H7 on dry and wet alfalfa seeds was investigated. The pathogen, at an initial population of 2.7 log10 cfu/g of seed, was not recovered by direct plating (< 0.7 log10 cfu/g) or enrichment of wet seeds exposed to 50 microl of AIT/950-cc jar for 24 h at 37 or 47 degrees C. Exposure of dry seeds containing 2.9 log10 cfu of E. coli O157:H7 per g to an atmosphere containing 100 microl of AIT/950-cc jar (ca. 105 ppm AIT if completely volatilized) for 24 h at 47 degrees C did not eliminate viable E. coli O157:H7 cells. Unfortunately, the enhanced effectiveness of AIT in killing the pathogen on wet alfalfa seeds is offset by a dramatic reduction in seed viability. Nevertheless, the use of AIT as an alternative to chlorine for the purpose of killing E. coli O157:H7 and perhaps other pathogens on alfalfa seed holds promise. Factors that may influence conditions rendering increased sensitivity of E. coli O157:H7 to AIT without compromising seed viability should be investigated.     

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.     

Survival of Salmonella typhimurium and Escherichia coli O157:H7 in cheese brines

Survival of Salmonella typhimurium and Escherichia coli O157:H7 was studied in model brines and brine from three cheese plants. Three strain mixtures of S. typhimurium and E. coli O157:H7 (10(6) CFU/ml) were inoculated separately into 23% model brine with or without added pasteurized whey (2%) and as a combined inoculum into the commercial brines. The model brines were incubated at 8 and 15 degrees C for 28 days, and the commercial brines at 4 and 13 degrees C for 35 days. Populations of both pathogens in the model brine + whey decreased slowly over 28 days (1.0-2.0 log CFU/ml) with greater survival at 8 degrees C than at 15 degrees C. Corresponding decreases in model brine without whey were 1.9-3.0 log CFU/ml, with greater survival at 8 degrees C than at 15 degrees C. Both S. typhimurium and E. coli O157:H7 survived significantly better (P < 0.05) at 4 degrees C than at 13 degrees C in two of the commercial brines. The survival of each pathogen in the commercial brines at 13 degrees C was significantly influenced by brine pH. Both pathogen populations decreased most rapidly in commercial brines during the first week of storage (2.5-4.0 and 2.3-2.8 log CFU/ml for S. typhimurium and E. coli O157:H7, respectively) with significant recovery (ca. 0.5 log CFU/ml increase) often occurring in the second week of storage. Counts changed little thereafter. Overall, E. coli O157:H7 survived better than S. typhimurium, with differences of 0.1-1.2 log CFU/ml between the two pathogens. Results of this study show that cheese brine could support the survival of contaminating S. typhimurium and E. coli O157:H7 for several weeks under typical brining conditions.     

Acquisition of antibiotic resistance plasmids by enterohemorrhagic Escherichia coli O157:H7 within rumen fluid

The emergence of antibiotic resistance among important foodborne pathogens like Escherichia coli O157:H7 has become an important issue with regard to food safety. In contrast to the case for Salmonella, antibiotic resistance has been slow in its development in E. coli O157:H7 despite the presence of mobile antibiotic resistance genes in other E. coli organisms that inhabit the same animal host. We set out to determine if rumen fluid influences the transfer of plasmid-mediated, antibiotic resistance to E. coli O157:H7. A commensal E. coli strain from a dairy cow was transformed with conjugative R plasmids and served as the donor in matings with naladixic acid-resistant E. coli O157:H7. R plasmids were transferred from the donor E. coli strain to E. coli O157:H7 in both Luria-Bertani (LB) broth and rumen fluid. R plasmids were transferred at a higher frequency to E. coli O157:H7 during 6 h of incubation in rumen fluid at rates comparable to those in LB broth, indicating that conditions in rumen fluid favor the transfer of the plasmids to E. coli O157. This finding suggests that the cow's rumen is a favorable environment for the genetic exchange of plasmids between microflora and resident E. coli O157:H7 in the bovine host.     

Survival of Listeria monocytogenes and Escherichia coli O157:H7 during sauerkraut fermentation

Sauerkraut was produced from shredded cabbage, as is typical in the United States, and from whole head cabbages, which is a traditional process in parts of Eastern Europe. The sauerkraut was inoculated with five strain mixtures of Escherichia coli O157:H7 and Listeria monocytogenes, and the populations of these bacteria, as well as lactic acid bacteria, pH, and titratable acidity, were monitored over the course of fermentation. Fermentation variables were temperature (18 and 22 degrees C) and salt concentration (1.8, 2.25, and 3%). For most of the analyses, the type of cabbage processing was a significant factor, although within cabbage type, neither salt nor fermentation temperature had significant effects. The final pH of the whole-head sauerkraut was lower than the shredded sauerkraut, but the titratable acidity was significantly higher in the shredded sauerkraut. E. coli O157:H7 and L. monocytogenes persisted in the brines for most of the fermentation, although at the end of the fermentations (15 days for shredded, 28 days for whole head), neither pathogen had detectable populations. E. coli populations decreased more rapidly in the shredded sauerkraut even though the pH was higher because of the higher total acidity in the shredded sauerkraut. Acid-tolerant strains of E. coli and L. monocytogenes were isolated from both shredded and whole-head sauerkraut at different salt concentrations and temperatures after 15 days of fermentation and could be detected at 35 days in the wholehead sauerkraut.     

Survival of Escherichia coli O157:H7 during storage in pressure-treated orange juice.

The effect of a high-pressure treatment on the survival of a pressure-resistant strain of Escherichia coli O157:H7 (NCTC 12079) in orange juice during storage at 3 degrees C was investigated over the pH range of 3.4 to 5.0. The pH of shelf-stable orange juice was adjusted to 3.4, 3.6, 3.9, 4.5, and 5.0 and inoculated with 10(8) CFU ml(-1) of E. coli O157:H7. The orange juice was then pressure treated at 400 MPa for 1 min at 10 degrees C or was held at ambient pressure (as a control). Surviving E. coli O157:H7 cells were enumerated at 1-day intervals during a storage period of 25 days at 3 degrees C. Survival of E. coli O157:H7 during storage was dependent on the pH of the orange juice. The application of high pressure prior to storage significantly increased the susceptibility of E. coli O157:H7 to high acidity. For example, after pressure treatment, the time required for a 5-log decrease in cell numbers was reduced from 13 to 3 days at pH 3.4, from 16 to 6 days at pH 3.6, and from >25 to 8 days at pH 3.9. It is evident that the use of high-pressure processing of orange juice in order to increase the juice's shelf-life and to inactivate pathogens has the added advantage that it sensitizes E. coli O157:H7 to the high acid conditions found in orange juice, which results in the survival of significantly fewer E. coli O157:H7 during subsequent refrigerated storage.     

Comparison of chemical treatments to eliminate enterohemorrhagic Escherichia coli O157:H7 on alfalfa seeds.

The focus of this study was to determine the efficacy of various chemicals in eliminating 2.04 to 3.23 log10 CFU/g of Escherichia coli O157:H7 from alfalfa seeds and to determine the survivability of the pathogen on seeds stored for prolonged periods at three temperatures. Significant (P < or = 0.05) reductions in populations of E. coli O157:H7 on inoculated seeds were observed after treatments with 500 and 1,000 ppm of active chlorine (as Ca[OCl]2) for 3 but not 10 min and with > or =2,000 ppm of Ca(OCl)2 regardless of pretreatment with a surfactant. Treatment with 20,000 ppm of active chlorine failed to kill 2.68 log10 CFU/g of seeds. Acidified NaClO2 (500 ppm) was effective in reducing populations of the pathogen by >2 logs per g. Acidified ClO2 significantly reduced populations of E. coli O157:H7 on seeds at concentrations > or =100 ppm, and 500 ppm of ClO2 reduced the pathogen from 2.7 log10 CFU/g to <0.5 CFU/g. Chlorine (as NaOCl) was not effective at concentrations < or =1,000 ppm; significant reduction was achieved only after treatment with 2,000 ppm for 3 or 10 min. Notable reduction in populations was observed after treatment with 30 or 70% C2H3OH, but there was a dramatic decrease in germination percentage. Treatment with 0.2% H2O2 significantly reduced populations, and the organism was not detected by direct plating after treatment with > or =1% H2O2. Significant reduction in population of E. coli O157:H7 occurred after treatment with 1% trisodium phosphate, 40 ppm of Tsunami and Vortexx, and 1% Vegi-Clean. A significant decrease in the number of E. coli O157:H7 on dry seeds was observed within 1 week of storage at 25 and 37 degrees C, but not at 5 degrees C. Between 1 and 38 weeks, populations on seeds stored at 5 degrees C remained relatively constant. The pathogen was recovered from alfalfa seeds initially containing 3.04 log 10 CFU/g after storage at 25 or 37 degrees C for 38 weeks but not 54 weeks.     

Inhibition of Escherichia coli O157:H7 in ripening dry fermented sausage by ground yellow mustard

Compounds generated by the enzymatic hydrolysis of glucosinolates naturally present in mustard powder are potently bactericidal against Escherichia coli O157:H7. Because E. coli O157:H7 can survive the dry fermented sausage manufacturing process, 2, 4, and 6% (wt/wt) nondeheated (hot) mustard powder or 6% (wt/wt) deheated (cold) mustard powder were added to dry sausage batter inoculated with E. coli O157:H7 at about 7 log CFU/g to evaluate the antimicrobial effectiveness of the powders. Reductions in E. coli O157:H7 populations, changes in pH and water activity (aw), effects on starter culture (Pediococcus pentosaceus and Staphylococcus carnosus) populations, and effects of mustard powder on sausage texture (shear) were monitored during ripening. Nondeheated mustard powder at 2, 4, and 6% in dry sausage (0.90 aw) resulted in significant reductions in E. coli O157:H7 (P < 0.05) of 3.4, 4.4, and 6.9 log CFU/g, respectively, within 30 days of drying. During fermentation and drying, mustard powder did not affect P. pentosaceus and S. carnosus activity in any of the treatments. Extension of drying to 36 and 48 days reduced E. coli O157:H7 by >5 log CFU/g in the 4 and 2% mustard powder treatments, respectively. The 6% deheated mustard powder treatment provided the most rapid reductions of E. coli O157:H7 (yielding <0.20 log CFU/g after 24 days) by an unknown mechanism and was the least detrimental (P < 0.05) to sausage texture.     

失活／存活模型在大肠杆菌O157：H7风险分析中的应用

目的研究出口分割鸡肉中大肠杆菌O157：H7的控制措施。方法建立了出口分割鸡肉中大肠杆菌O157：H7在速冻过程中的失活模型和在-18℃下的存活模型,通过风险分析提出控制措施。结果利用所建模型定量描述了出口分割鸡肉从成品到消费过程中大肠杆菌O157：H7带菌量的变化,得出摄入1份鸡肉感染大肠杆菌O157：H7病的风险。结论本研究提出的控制措施可提高出口分割鸡肉的安全性。