Bactericidal effect of sodium chlorate on Escherichia coli O157:H7 and Salmonella typhimurium DT104 in rumen contents in vitro

Escherichia coli O157:H7 and Salmonella Typhimurium DT104 are important foodborne pathogens affecting the beef and dairy industries and strategies are sought to rid these organisms from cattle at slaughter. Both pathogens possess respiratory nitrate reductase that also reduces chlorate to the lethal chlorite ion. Because most anaerobes lack respiratory nitrate reductase, we hypothesized that chlorate may selectively kill E. coli O157:H7 and Salmonella Typhimurium DT104 but not potentially beneficial anaerobes. In support of this hypothesis, we found that concentrations of E. coli O157:H7 and Salmonella Typhimurium DT104 were reduced from approximately 1,000,000 colony forming units (CFU) to below our level of detection (< or = 10 CFU) following in vitro incubation (24 h) in buffered ruminal contents (pH 6.8) containing 5 mM added chlorate. In contrast, chlorate had little effect on the most probable number (mean +/- SD) of total culturable anaerobes (ranging from 9.9 +/- 0.72 to 10.7 +/- 0.01 log10 cells/ml). Thus, chlorate was bactericidal to E. coli O157:H7 and Salmonella Typhimurium DT104 but not to potentially beneficial bacteria. The bactericidal effect of chlorate was concentration dependent (less at 1.25 mM) and markedly affected by pH (more bactericidal at pH 6.8 than pH 5.6).     

Effect of oral sodium chlorate administration on Escherichia coli O157:H7 in the gut of experimentally infected pigs.

Strategies are sought to reduce pathogenic Escherichia coli concentrations in food animals. Because E. coli possess respiratory nitrate reductase activity, which also reduces chlorate to cytotoxic chlorite, we tested and found that oral sodium chlorate administration reduced gut concentrations of E. coli O157:H7 in experimentally infected pigs and wildtype E. coli concentrations in nonchallenged pigs. Mean +/- S.E. concentrations (log10 CFU/g) of E. coli O157:H7 in ileal, cecal, colonic and rectal contents from placebo-treated pigs were 4.03 +/- 0.66, 3.82 +/- 0.24, 4.42 +/- 0.25 and 4.03 +/- 0.16, respectively. In contrast, E. coli O157:H7 concentrations were reduced (P < 0.05) in ileal (1.56 +/- 0.22) cecal (2.65 +/- 0.38), colonic (3.05 +/- 0.38) and rectal (3.00 +/- 0.29) contents from pigs orally administered three successive (8 h apart) 10-ml doses of 100 mM chlorate. Wildtype E. coli concentrations in gut contents of non-E. coli O157:H7-challenged pigs likewise treated with chlorate were reduced by 1.1 to 4.5 log10 units compared to concentrations in placebo-treated pigs, which exceeded 6.0 log10 CFU/g. As before, the reductions were greater in anterior regions of the gut than regions more caudal. Similar treatment of E. coli O157:H7-challenged pigs with 200 mM chlorate caused reductions in gut concentrations of E. coli O157:H7; however, the reductions were not necessarily greater than those achieved with the 100 mM chlorate treatment.     

流式分析技术快速定量检测牛乳中大肠杆菌O157:H7

建立一种基于流式分析技术的快速定量检测牛乳中大肠杆菌O157:H7的方法。用偶联有异硫氰酸荧光素的大肠杆菌O157单克隆抗体对大肠杆菌O157:H7进行特异性标记,通过优化抗体反应条件,建立流式检测方法,然后对磷酸盐缓冲溶液（phosphate buffer saline,PBS）和人工污染牛乳样品中不同浓度的大肠杆菌O157:H7进行定量检测。本研究建立的流式检测方法的在PBS中的检测范围为2.57×103～1.12×108?CFU/mL,灵敏度达到2.57×103?CFU/mL。将所建立的流式检测方法应用于牛乳样品检测,当人工污染牛乳样品中大肠杆菌O157:H7的浓度在2.31×104～1.48×108?CFU/mL之间时,流式检测方法与平板计数方法检测结果基本一致,方法的灵敏度为2.31×104?CFU/mL,检测时间为35?min。该方法能快速、定量地检测出牛乳样品中的大肠杆菌O157:H7,在食源性致病菌的快速筛查和监控中具有重要的应用价值。     

Effect of rumen protozoa on Escherichia coli O157:H7 in the rumen and feces of specifically faunated sheep

The effects of rumen protozoal populations on ruminal populations and fecal shedding of Escherichia coli O157:H7 were evaluated by using specifically faunated sheep. Nine fauna-free sheep (three animals per treatment) were inoculated with Dasytricha spp. (DAS sheep); with mixed population A (PopA) comprising Entodinium spp., Isotricha spp., Diplodinium spp., and Polyplastron spp.; or with mixed population B (PopB) comprising Entodinium spp., Isotricha spp., Dasytricha spp., and Epidinium spp.; six sheep were maintained fauna-free (FF sheep) to serve as controls. Sheep were fed barley silage-based diets, and treatment groups were housed in isolated rooms. Sheep were inoculated orally with 10(10) CFU of a four-strain mixture of nalidixic acid-resistant E. coli O157:H7. Samples of ruminal fluid and feces were collected over 77 days. Polyplastron spp. were detected in only one sheep in PopA, and Dasytricha spp. were detected only once within the PopB cohort. Sheep in the DAS group were 2.03 times more likely (P < 0.001) to shed E. coli O157:H7 than were those in the other three treatments, whereas the PopB sheep were less likely (0.65; P < 0.05) to shed this bacterium. The likelihood of harboring ruminal E. coli O157:H7 also tended (P = 0.06) to be higher in DAS and was lower (P < 0.01) in FF than in other cohorts. Possibly, Dasytricha spp. had a hosting effect, and Epidinium spp. had a predatory relationship, with E. coli O157:H7. Additional study into predator-prey and hosting relationships among rumen protozoa and E. coli O157:H7 is warranted.     

Inactivation of escherichia coli O157:H7 in cattle drinking water by sodium caprylate

Escherichia coli O157:H7 is an important foodborne pathogen. Cattle serve as one of the major reservoirs of E. coli O157:H7, excreting the pathogen in feces. Environmental persistence of E. coli O157:H7 is critical in its epidemiology on farms, and the pathogen has been isolated from cattle water troughs. Thus, there is a need for an effective method for killing E. coli O157:H7 in cattle drinking water. In this study, the efficacy of sodium caprylate for killing E. coli O157:H7 in cattle drinking water was investigated. A four-strain mixture of E. coli O157:H7 was inoculated (6.0 log CFU/ml) into 100-ml samples of well water containing 0, 75, 100, or 120 mM sodium caprylate. Water samples containing 1% (wt/vol) bovine feces or feed also were included. The samples were incubated at 21 or 8 degrees C for 21 days. Water samples were analyzed for viable E. coli O157:H7 on days 0, 1, 3, 5, and 7 and weekly thereafter. Triplicate samples of each treatment and control were included, and the study was repeated twice. The magnitude of E. coli O157:H7 inactivation in water significantly increased (P < 0.01) with increases in caprylate concentration and storage temperature. At 120 mM, sodium caprylate completely inactivated E. coli O157:H7 in all the samples after 1 to 20 days, depending on the treatments. The presence of feces or feed also had a significant effect (P < 0.01) on the antibacterial property of caprylate; the presence of feces decreased the antibacterial effect, whereas addition of feed enhanced the effect. These results indicate that sodium caprylate is effective in killing E. coli O157:H7 in cattle drinking water, but detailed cattle palatability studies of water containing caprylate are necessary.     

Use of steam condensing at subatmospheric pressures to reduce Escherichia coli O157:H7 numbers on bovine hide.

This study used a laboratory-scale apparatus to apply subatmospheric steam to bovine hide pieces inoculated with Escherichia coli O157:H7 in maximum recovery diluent (MRD) and in high-liquid content and low-liquid content fecal suspensions (HLC fecal and LLC fecal, respectively). The survival of the organism in fecal clods, which were stored for 24 days in a desiccated state, was assessed. Inoculated fecal clods were also treated with subatmospheric steam. Steam treatment at 80 +/- 2 degrees C for 20 s reduced E. coli O157:H7 concentrations on hide inoculated to initial concentrations of approximately 7 log10 CFU/g by 5.46 (MRD inoculum), 4.17 (HLC fecal inoculum), and 5.99 (LLC fecal inoculum) log10 CFU/g. The reductions achieved in samples inoculated with LLC feces were larger than in samples inoculated with HLC feces (P < 0.05). Treatment at 80 +/- 2 degrees C for 10 s resulted in significantly smaller reductions (P < 0.05) on hide pieces of 2.54 (MRD), 1.94 (HLC fecal), and 2.15 (LLC fecal) log10 CFU/g. There were no significant differences among the reductions observed in all inoculum types in samples treated for 10 s. E. coli O157:H7 inoculated in fecal clods to 7.78 log10 CFU/g and stored at 4 or 15 degrees C survived for at least 24 days. Steam treatment (20 s) of 3-day-old clods reduced surviving E. coli O157:H7 numbers from 4.20 log10 CFU/g to below the limit of detection of the assay used (1.20 log10 CFU/g). This study shows that steam condensing at or below 80 +/- 2 degrees C can reduce E. coli O157:H7 when present on bovine hide, reducing the risk of cross contamination to the carcass during slaughter and dressing.     

Effect of modified atmosphere packaging on the persistence and expression of virulence factors of Escherichia coli O157:H7 on shredded iceberg lettuce

Fresh-cut leafy greens contaminated with Escherichia coli O157:H7 have caused foodborne outbreaks. Packaging conditions, coupled with abusive storage temperatures of contaminated lettuce, were evaluated for their effect on the potential virulence of E. coli O157:H7. Shredded lettuce was inoculated with 5.58 and 3.98 log CFU E. coli O157:H7 per g and stored at 4 and 15°C, respectively, for up to 10 days. Lettuce was packaged under treatment A (modified atmosphere packaging conditions used for commercial fresh-cut produce, in gas-permeable film with N(2)), treatment B (near-ambient air atmospheric conditions in a gas-permeable film with microperforations), and treatment C (high-CO(2) and low-O(2) conditions in a gas-impermeable film). E. coli O157:H7 populations from each treatment were determined by enumeration of numbers on MacConkey agar containing nalidixic acid. RNA was extracted from packaged lettuce for analysis of expression of virulence factor genes stx(2), eae, ehxA, iha, and rfbE. E. coli O157:H7 populations on lettuce at 4°C under all treatments decreased, but most considerably so under treatment B over 10 days. At 15°C, E. coli O157:H7 populations increased by at least 2.76 log CFU/g under all treatments. At 15°C, expression of eae and iha was significantly greater under treatment B than it was under treatments A and C on day 3. Similarly, treatment B promoted significantly higher expression of stx(2), eae, ehxA, and rfbE genes on day 10, compared with treatments A and C at 15°C. Results indicate that storage under near-ambient air atmospheric conditions can promote higher expression levels of O157 virulence factors on lettuce, and could affect the severity of E. coli O157:H7 infections associated with leafy greens.     

Antimicrobial activity of a 14-residue synthetic peptide against foodborne microorganisms

A chemically synthesized short-chain peptide composed of six leucine and eight lysine (6K8L) residues was demonstrated to be biocidal against several foodborne organisms including Escherichia coli O157:H7, Listeria monocytogenes, Pseudomonas fluorescens, and Kluyveromyces marxianus suspended in phosphate buffer at concentrations of 5 to 50 microg/ml. All strains were reduced by 3 log10 CFU/ml within 10 min at peptide concentrations of <10 microg/ml. The peptide reduced by 3 log10 CFU/ml E. coli O157:H7 counts in apple juice and was active over the pH range of 3.5 to 7. Peptide concentrations of 100 microg/ml inhibited the aerobic and anaerobic microorganisms present in meat exudate liquid. However, the peptide was not effective against E. coli O157:H7 in skim milk at concentrations up to 100 microg/ml.     

Biological control of postharvest decays of apple can prevent growth of Escherichia coli O157:H7 in apple wounds

Fresh cells of the antagonist Pseudomonas syringae at 2.4 x 10(8) CFU/ml inoculated into wounds of 'Golden Delicious' apple prevented Escherichia coli O157:H7 (concentrations ranging from 2.4 x 10(5) to 2.4 x 10(7) CFU/ml) from growing in the wounds. This occurred when the two microorganisms were co-inoculated or inoculation with E. coli O157:H7 was conducted 1 or 2 days after inoculation with the antagonist. In similar tests, application of the commercial formulation of this antagonist prevented the growth of E. coli O157:H7 in wounds when inoculated 1 or 2 days after application of the antagonist. Populations of E. coli O157:H7 in wounds treated with water (control) before inoculation with this pathogen increased approximately 2 log units during the first 48 h after inoculation. These results indicate that biocontrol agents developed for controlling storage decays of fruits may have the additional benefit of preventing the growth of foodborne pathogens in freshly wounded tissue of intact and fresh-cut fruits.     

Escherichia coli O157:H7 populations in ruminants can be reduced by orange peel product feeding

Foodborne pathogenic bacteria such as Escherichia coli O157:H7 are threats to the safety of beef. Citrus peel and dried orange pulp are by-products from citrus juice production that have natural antimicrobial effects and are often incorporated into least-cost ration formulations for beef and dairy cattle. This study was designed to determine if orange peel and pulp affected E. coli O157:H7 populations in vivo. Sheep (n = 24) were fed a cracked corn grain-based diet that was supplemented with a 50-50 mixture of dried orange pellet and fresh orange peel to achieve a final concentration (dry matter basis, wt/wt) of 0, 5, or 10% pelleted orange peel (OP) for 10 days. Sheep were artificially inoculated with 10(10) CFU of E. coli O157:H7 by oral dosing. Fecal shedding of E. coli O157:H7 was measured daily for 5 days after inoculation, after which all animals were humanely euthanized. At 96 h postinoculation, E. coli O157:H7 shedding was reduced (P < 0.05) in sheep fed 10% OP. Populations of inoculated E. coli O157:H7 were reduced by OP treatment throughout the gastrointestinal tract; however, this reduction reached significant levels in the rumen (P < 0.05) of sheep fed 10% OP diets. Cecal and rectal populations of E. coli O157:H7 were reduced (P < 0.05) by inclusion of both 5 and 10% OP diets. Our results demonstrate that orange peel products can be used as a preharvest intervention strategy as part of an integrated pathogen reduction scheme.     

Bactericidal effects of Lactobacillus reuteri and allyl isothiocyanate on Escherichia coli O157:H7 in refrigerated ground beef

Two naturally occurring antimicrobial agents were tested in packages of refrigerated ground beef for their ability to reduce the viability of Escherichia coli O157:H7 during storage. Allyl isothiocyanate (AITC) and Lactobacillus reuteri were tested separately and together for their action against a cocktail of five strains of E. coli O157:H7 in ground beef held at 4 degrees C for 25 days. Ground beef prepared from whole, raw inside round beef roasts was inoculated with low (3 log CFU/g) or high (6 log CFU/g) levels of the E. coli O157:H7 mixture. The beef was treated with AITC (about 1,300 ppm), L. reuteri, or both, along with 250 mM of glycerol per kg of meat at two levels (3 and 6 log CFU/g) and according to a design that yielded 8 controls plus 10 different treatments. Samples were analyzed for E. coli O157:H7 survivors, numbers of total bacteria, and lactic acid bacteria on days 0 to 25 at 5-day intervals. L. reuteri at both input levels with glycerol killed E. coli O157:H7 at both inoculated levels before day 20. AITC completely eliminated E. coli O157:H7 at the low-inoculum level (3 log CFU/g) and reduced viability >4.5 log CFU/g at the high-inoculum level (6 log CFU/g) by the end of the storage period. The combination of L. reuteri and AITC did not yield an additive effect against E. coli O157:H7 viability. L. reuteri in the presence of glycerol was highly effective against E. coli O157:H7 in ground beef during refrigerated storage (4 degrees C) in modified atmosphere packages. Sensory testing is planned to evaluate effects of treatments.     

In vitro inactivation of Escherichia coli O157:H7 in bovine rumen fluid by caprylic acid

The antibacterial effect of caprylic acid (35 and 50 mM) on Escherichia coli O157:H7 and total anaerobic bacteria at 39 degrees C in rumen fluid (pH 5.6 and 6.8) from 12 beef cattle was investigated. The treatments containing caprylic acid at both pHs significantly reduced (P < 0.05) the population of E. coli O157:H7 compared with that in the control samples. At pH 5.6, both levels of caprylic acid killed E. coli O157:H7 rapidly, reducing the pathogen population to undetectable levels at 1 min of incubation (a more than 6.0-log CFU/ml reduction). In buffered rumen fluid at pH 6.8, 50 mM caprylic acid reduced the E. coli O157:H7 population to undetectable levels at 1 min of incubation, whereas 35 mM caprylic acid reduced the pathogen by approximately 3.0 and 5.0 log CFU/ml at 8 and 24 h of incubation, respectively. At both pHs, caprylic acid had a significantly lesser (P < 0.05) and minimal inhibitory effect on the population of total anaerobic bacteria in rumen compared with that on E. coli O157:H7. At 24 h of incubation, caprylic acid (35 and 50 mM) reduced the population of total anaerobic bacteria by approximately 2.0 log CFU/ml at pH 5.6, whereas at pH 6.8, caprylic acid (35 mM) did not have any significant (P > 0.05) inhibitory effect on total bacterial load. Results of this study revealed that caprylic acid was effective in inactivating E. coli O157:H7 in bovine rumen fluid, thereby justifying its potential as a preslaughter dietary supplement for reducing pathogen carriage in cattle.     

Development of an experimental model to assess the ability of Escherichia coli O157:H7-inoculated fecal pats to mimic a super shedder within a feedlot environment

This study was conducted to develop an experimental model that could assess the ability of Escherichia coli O157:H7-inoculated fecal pats to mimic a super shedder (>10(4) CFU/g of feces) within a feedlot environment. The day before the study began, 48 steers that had been negative for E. coli O157:H7 in feces for three consecutive weeks were sorted into three treatment groups, with two replicate pens per treatment and 8 steers per pen. Steers within the pens (20.50 by 10.75 m) were exposed to control feces or feces inoculated with two levels of a mixture of five strains of nalidixic acid-resistant E. coli O157:H7 (low level, 10(2) CFU/g; high level, 10(5) CFU/g). Five 300-g fecal pats were introduced into the pens twice daily (10:00 a.m. and 2:30 p.m.) on days 0 through 6 and days 14 through 20. Pats were placed in the pen at random locations to mimic defecation of a steer within the pen. Fecal grab samples, hide swab samples (500-cm2 area of the rump), natural fecal pat samples (freshly voided), and rope samples (1.22-m-long manila rope) where obtained at multiple times during the 49-day trial to evaluate the spread of nalidixic acid-resistant E. coli O157:H7 throughout the feedlot environment and among penmates. Immunomagnetic separation and selective media were used to detect E. coli O157:H7. Nalidixic acid-resistant E. coli O157:H7 was detected in 13 high-level treatment fecal grab samples, 7 high-level treatment hide swab samples, 1 low-level hide swab sample, and 2 high-level rope samples. For both fecal grab and hide swab samples, the overall prevalence of E. coli O157:H7 in the high-level group was greater (P < 0.01) than that for the pooled low-level and control groups. Addition of inoculated fecal pats to pens increased transmission of E. coli O157:H7 among penmates, but cattle that acquired E. coli O157:H7 shed the bacterium for only a short time at low levels. Transmission of E. coli O157:H7 from the feces of super shedders to naive penmates may contribute to the observed transient nature of shedding of E. coli O157:H7 among feedlot cattle.     

Transportation and lairage environment effects on prevalence, numbers, and diversity of Escherichia coli O157:H7 on hides and carcasses of beef cattle at processing

Hide has been established as the main source of carcass contamination during cattle processing; therefore, it is crucial to minimize the amount of Escherichia coli O157:H7 on cattle hides before slaughter. Several potential sources of E. coli O157: H7 are encountered during transportation and in the lairage environment at beef-processing facilities that could increase the prevalence and numbers of E. coli O157:H7 on the hides of cattle. On three separate occasions, samples were obtained from cattle at the feedlot and again after cattle were stunned and exsanguinated at the processing plant (286 total animals). The prevalence of E. coli O157:H7 on hides increased from 50.3 to 94.4% between the time cattle were loaded onto tractor-trailers at the feedlot and the time hides were removed in the processing plant. Before transport, nine animals had E. coli O157:H7 in high numbers (> 0.4 CFU/cm2) on their hides. When sampled at the slaughter facility, the number of animals with high hide numbers had increased to 70. Overall, only 29% of the E. coli O157:H7 isolates collected postharvest (221 of 764) matched pulsed-field gel electrophoresis types collected before transport. The results of this study indicate that transport to and lairage at processing plants can lead to increases in the prevalence and degree of E. coli O157:H7 contamination on hides and the number of E. coli O157:H7 pulsed-field gel electrophoresis types associated with the animals. More study is needed to confirm the mechanism by which additional E. coli O157:H7 strains contaminate cattle hides during transport and lairage and to design interventions to prevent this contamination.     

Antibacterial effect of monocaprylin on Escherichia coli O157:H7 in apple juice

The antibacterial effect of low concentrations of monocaprylin on Escherichia coli O157:H7 in apple juice was investigated. Apple juice alone (control) or containing 2.5 mM (0.055%) or 5 mM monocaprylin was inoculated with a five-strain mixture of E. coli O157:H7 at approximately 6.0 log CFU/ml. The juice samples were stored at 23 or 4 degrees C for 14 or 21 days, respectively, and the population of E. coli O157:H7 was determined on tryptic soy agar plates supplemented with 0.6% yeast extract. At both storage temperatures, the population of E. coli O157:H7 in monocaprylin-supplemented juice samples was significantly lower (P < 0.05) than that in the control samples. The concentration of monocaprylin and the storage temperature had a significant effect on the inactivation of E. coli O157:H7 in apple juice. Monocaprylin at 5 mM was significantly more effective than 2.5 mM monocaprylin for killing E. coli O157:H7 in apple juice. Inactivation of E. coli O157:H7 by monocaprylin was more pronounced in juice stored at 23 degrees C than in the refrigerated samples. Results of this study indicated that monocaprylin is effective for killing E. coli O157:H7 in apple juice, but detailed sensory studies are needed to determine the organoleptic properties of apple juice containing monocaprylin.     

Pathogenicity of enterohemorrhagic Escherichia coli in neonatal calves and evaluation of fecal shedding by treatment with probiotic Escherichia coli

The pathogenicity and fecal shedding of enterohemorrhagic Escherichia coli (EHEC) O26:H11, O111:NM, and O157:H7 were compared in calves (< 1 week of age) with or without prior treatment with probiotic bacteria (competitive exclusion E. coli). Three groups of 12 to 14 calves were used for these treatments. Half of the calves in each group were perorally administered 10(10) CFU of probiotic bacteria per calf, and, 2 days thereafter, 10(8) CFU of a five-strain mixture with one of the three EHEC serotypes per calf were administered to each calf. None of the EHEC serotypes caused clinical disease,and neither gross nor microscopic lesions attributable to EHEC were detected in control or probiotic-treated calves at necropsy. In calves administered E. coli O157:H7, fecal shedding was greatly reduced (> 6 log10 CFU/g) by 8 days after administration, and there was no significant difference (P > 0.05) in fecal shedding of E. coli O157:H7 between probiotic-treated and untreated control groups at that time. In contrast, control calves perorally administered E. coil of serotypes O111:NM or O26:H11 continued to shed substantial populations (10(2.1) to 10(6) CFU/g of feces and 10(2.5) to 10(4.9) CFU/g of feces, respectively) throughout 7 days postadministration of EHEC. In both groups administered either E. coli O111:NM or O26:H11, significantly less (P < 0.05) EHEC was isolated from feces at 7 days postadministration of EHEC and at necropsy from theprobiotic-treated group than from the untreated control group. Overall, neonatal calves shed in the feces from 1 to 7 days following peroral administration of EHEC greater populations of E. coli O111:NM and O26:H111 than E. coli O157:H7. In addition, treatment of calves with probiotic E. coli reduced fecal shedding of E. coli O111:NM and O26:H11 in most calves.     

Sensitive detection of Escherichia coli O157:H7 by conventional plating techniques

The direct detection and estimation of concentration of Escherichia coli O157:H7 down to 1 CFU/g of cheese was achieved by conventional plating techniques. Cheese was manufactured with unpasteurized milk inoculated with E. coli O157: H7 at 34 +/- 3 CFU/ml. The numbers of E. coli O157:H7 were monitored during cheese ripening by plating on sorbitol MacConkey agar supplemented with cefixime and potassium tellurite (CT-SMAC) and on CT-O157:H7 ID medium. Using the pour plate method, E. coli O157:H7 colonies could easily be distinguished from non-O157:H7 colonies on CT-O157:H7 ID medium but not on CT-SMAC. Higher numbers of E. coli O157:H7 were detectable with O157:H7 ID medium. Latex agglutination and PCR were used to confirm the identification of typical E. coli O157:H7 colonies, and nontypical colonies as not being E. coli O157:H7. As few as 1 CFU/g of cheese could be detected. E. coli O157:H7 also was detected in deliberately contaminated milk at concentrations as low as 4 CFU/10 ml.     

Escherichia coli O157:H7, Campylobacter jejuni, and Salmonella Prevalence in cull dairy cows marketed in northeastern Ohio

Preharvest management factors are predicted to impact the prevalence of foodborne pathogens in cattle sent to slaughter. We simultaneously examined the prevalence and antibiotic resistance patterns of Campylobacter jejuni, Salmonella, and Escherichia coli O157:H7 isolated from cull dairy cattle at two livestock auctions in northeastern Ohio. Between April and September 2002, a total of 1,026 fecal samples were collected. C. jejuni was isolated from 48 of 686 (7%) fecal samples, Salmonella was isolated from 39 of 585 (6.7%) samples, and E. coli O157:H7 was isolated from 21 of 1,026 (2.1%) samples. Of the 585 samples tested for all three pathogens, at least one pathogen was identified in 86 of 585 (15%) samples. One sample was positive for both E. coli O157:H7 and C. jejuni, and five samples yielded both C. jejuni and Salmonella. Size of herd of origin could be traced for 75 to 85% of samples collected. Salmonella was isolated at higher frequencies from herds larger than 60 cattle than from smaller herds (9.0 versus 3.5%, P = 0.02). In contrast, size of herd of origin did not significantly affect the E. coli O157:H7 and C. jejuni prevalence. Approximately 90% of Salmonella and E. coli O157:H7 isolates were pansensitive to a panel of 16 antibiotics. Thirty-six percent of C. jejuni isolates were resistant to tetracycline. In this study, antibiotic resistance among the foodborne pathogens isolated from cull diary cattle was rare. Although size of dairy herd of origin was positively associated with Salmonella prevalence, herd size was not strongly associated with E. coli O157:H7 and C. jejuni prevalence in market dairy cattle. These results can be used to assess the food safety risks associated with the slaughter of cull dairy cattle.     

Survival of enterohemorrhagic Escherichia coli O157:H7 in retail mustard

Escherichia coli O157:H7 survival in acid foods such as unpasteurized apple cider and fermented sausage is well documented. Researchers have determined that E. coli O157:H7 can survive in refrigerated acid foods for weeks. The potential of acid foods to serve as a vector of E. coli O157:H7 foodborne illness prompted this study to determine the fate of this organism in retail mustard containing acetic acid when stored at room and refrigerated temperatures. Various retail brands of dijon, yellow, and deli style mustard, pH ranging from 3.17 to 3.63, were inoculated individually with three test strains of E. coli O157:H7. Samples were inoculated with approximately 1.0 x 10(6) CFU/g, incubated at room (25+/-2.5 degrees C) and refrigerated (5+/-3 degrees C) temperatures, and assayed for surviving test strains at predetermined time intervals. An aliquot was appropriately diluted and plated using sorbitol MacConkey agar (SMAC). When the test strain was not recoverable by direct plating, the sample was assayed by enrichment in modified tryptic soy broth and recovered using SMAC. Growth of E. coli O157:H7 test strains was inhibited in all retail mustard styles. E. coli O157:H7 was not detected in dijon style mustard beyond 3 h at room and 2 days at refrigerated temperatures. Survival in yellow and deli style mustard was not detected beyond 1 h. Overall, test strain survival was greater at refrigerated than room temperature. Retail mustard demonstrated the ability to eliminate effectively any chance contamination by this organism within hours to days, suggesting that these products are not a likely factor in E. coli O157:H7 foodborne illness.     

Shiga toxin-producing Escherichia coli in beef heifers grazing an irrigated pasture

Shiga toxin-producing Escherichia coli (STEC) produce toxins that have been associated with several human illnesses. E. coli O157:H7 is the most well-studied STEC and was first associated with consumption of improperly cooked ground beef in 1982. E. coli O157:H7 is not the only foodborne STEC because other STEC serotypes are also associated with human illnesses. The objective of this study was to assess prevalence of STEC in 23 yearling beef (Angus) heifers grazing an irrigated grass pasture in spring (April), summer (July), fall (October), and winter (December) of 1999. A total of 86 fecal samples were rectally collected and were subjected to microbiological testing for the presence of STEC. Nine E. coli isolates from five heifers (one in spring and fall and three in winter) were toxic to Vero cells. Of these isolates, four were E. coli O157:H7, two belonged to the serogroup O6, one O39:NM, one O113:H-, and the final isolate was untypable. The STEC prevalence rate in our herd ranged from 4% (spring) to 15% (winter). Based on detecting both O157:H7 and non-O157:H7 STEC in our heifers, it is clear that screening fecal samples should not be limited to E. coli O157:H7. Identification of STEC-positive cattle prior to slaughter should help in reducing the risk of beef contamination with such foodborne pathogens if pre- and/or postharvest control measures are applied to such animals.