Inactivation of Shiga toxin-producing O157:H7 and non-O157:H7 Shiga toxin-producing Escherichia coli in brine-injected, gas-grilled steaks

We quantified translocation of Escherichia coli O157:H7 (ECOH) and non-O157:H7 verocytotoxigenic E. coli (STEC) into beef subprimals after brine injection and subsequently monitored their viability after cooking steaks cut therefrom. Beef subprimals were inoculated on the lean side with ca. 6.0 log CFU/g of a five-strain cocktail of rifampin-resistant ECOH or kanamycin-resistant STEC, and then passed once through an automatic brine-injector tenderizer, with the lean side facing upward. Brine solutions (9.9% ± 0.3% over fresh weight) consisted of 3.3% (wt/vol) of sodium tripolyphosphate and 3.3% (wt/vol) of sodium chloride, prepared both with (Lac(+), pH = 6.76) and without (Lac(-), pH = 8.02) a 25% (vol/vol) solution of a 60% potassium lactate-sodium diacetate syrup. For all samples injected with Lac(-) or Lac(+) brine, levels of ECOH or STEC recovered from the topmost 1 cm (i.e., segment 1) of a core sample obtained from tenderized subprimals ranged from ca. 4.7 to 6.3 log CFU/g; however, it was possible to recover ECOH or STEC from all six segments of all cores tested. Next, brine-injected steaks from tenderized subprimals were cooked on a commercial open-flame gas grill to internal endpoint temperatures of either 37.8 °C (100 °F), 48.8 °C (120 °F), 60 °C (140 °F), or 71.1 °C (160 °F). Regardless of brine formulation or temperature, cooking achieved reductions (expressed as log CFU per gram) of 0.3 to 4.1 of ECOH and 0.5 to 3.6 of STEC. However, fortuitous survivors were recovered even at 71.1 °C (160 °F) for ECOH and for STEC. Thus, ECOH and STEC behaved similarly, relative to translocation and thermal destruction: Tenderization via brine injection transferred both pathogens throughout subprimals and cooking highly contaminated, brine-injected steaks on a commercial gas grill at 71.1 °C (160 °F) did not kill all cells due, primarily, to nonuniform heating (i.e., cold spots) within the meat.     

Serotypes and virulence genes of ovine non-O157 Shiga toxin-producing Escherichia coli in Switzerland

Sixty ovine STEC strains were examined with the aim (i) to serotype the strains, (ii) to characterize virulence factors, and (iii) to discuss possible associations between these factors and to assess the potential pathogenicity of these strains for humans. The 60 sorbitol-positive, non-O157 STEC strains belonged to 19 O:H serotypes, whereas 68% were of five serotypes (O87:H16, O91:H-, O103:H2, O128:H2, O176:H4). 52% belonged to serotypes reported in association with HUS. Five serotypes were not previously reported in sheep strains. Of the 47 strains encoding for stx1 variants, 57% were stx1c- and of the 45 encoding for stx2 variants, 80% were stx2d-positive. Eighty-two percent of the strains showed further putative virulence factors: 13% were eae-, 60% ehxA- and 67% saa-positive. The associations between harboring (i) eae and stx1, stx2, ehxA or no saa and (ii) saa and stx1c or stx2d were significant (P<0.05). The strains belonged to 27 seropathotypes (association between serotypes and virulence factors), but 57% belonged to only six and O91:H-stx1 stx2d saa and O128:H2 stx1c stx2d ehxA saa were the most common. Seven of the eight intimin-positive strains harbored eae. Four strains of serotype O103:H2 and O121:H10 harboring stx2, eae and ehxA showed virulence factors typical for strains associated with severe human disease. However, according to the virulence factors, the majority of the ovine non-O157 STEC strains are assumed low-virulence variants. Nevertheless, as long as the contribution and interaction of these factors in milder disease remains unclear P, a certain risk for humans cannot be excluded.     

Mathematical modeling of growth of non-O157 Shiga toxin-producing Escherichia coli in raw ground beef

Abstract: The objective of this study was to investigate the growth of Shiga toxin‐producing Escherichia coli (STEC, including serogroups O45, O103, O111, O121, and O145) in raw ground beef and to develop mathematical models to describe the bacterial growth under different temperature conditions. Three primary growth models were evaluated, including the Baranyi model, the Huang 2008 model, and a new growth model that is based on the communication of messenger signals during bacterial growth. A 5 strain cocktail of freshly prepared STEC was inoculated to raw ground beef samples and incubated at temperatures ranging from 10 to 35 °C at 5 °C increments. Minimum relative growth (<1 log₁₀ cfu/g) was observed at 10 °C, whereas at other temperatures, all 3 phases of growth were observed. Analytical results showed that all 3 models were equally suitable for describing the bacterial growth under constant temperatures. The maximum cell density of STEC in raw ground beef increased exponentially with temperature, but reached a maximum of 8.53 log₁₀ cfu/g of ground beef. The specific growth rates estimated by the 3 primary models were practically identical and can be evaluated by either the Ratkowsky square‐root model or a Bělehrádek‐type model. The temperature dependence of lag phase development for all 3 primary models was also developed. The results of this study can be used to estimate the growth of STEC in raw ground beef at temperatures between 10 and 35 °C. Practical Application: Incidents of foodborne infections caused by non‐O157 Shiga toxin‐producing Escherichia coli (STEC) have increased in recent years. This study reports the growth kinetics and mathematical modeling of STEC in ground beef. The mathematical models can be used in risk assessment of STEC in ground beef.     

Isolation and characterization of Shiga toxin-producing Escherichia coli O157:H7 and non-O157 from beef carcasses at a slaughter plant in Mexico

The contamination of beef carcasses with Shiga toxin-producing O157:H7 and non-O157 Escherichia coli (STEC) obtained from a slaughter plant in Guadalajara, Mexico was investigated. A total of 258 beef carcasses were sampled during a 12-month period. All samples were assayed for STEC by selective enrichment in modified tryptone soy broth supplemented with cefixime, cefsulodin and vancomycin, followed by plating on Sorbitol MacConkey Agar supplemented with cefixime and tellurite (CT-SMAC). Simultaneously, all samples were assayed by immunomagnetic separation (IMS) and plated on CT-SMAC and CHROMagar. The presence of the stx1, stx2, eaeA and hly933 genes, recognized as major virulence factors of STEC, was tested for O157:H7 and non-O157 E. coli isolates by multiplex polymerase chain reaction (PCR). STEC was detected in two (0.8%) samples. One of these STEC isolates corresponded to the serotype O157:H7 showing stx2, eaeA and hyl933 genes. The other isolate corresponded to non-O157 STEC and only had the stx1 gene. Thirteen carcasses (5%) were positive for nonmotile E. coli O157 and 7 (2.7%) were positive for E. coli O157:H7. The presence of O157:H7 and non-O157 STEC on beef carcasses in this slaughter plant in Guadalajara, Mexico, emphasizes the importance of implementing the Hazard Analysis and Critical Control Point (HACCP) system, as well as the need for implementing, evaluating, and validating antimicrobial interventions to reduce the presence of potential pathogenic microorganisms.     

Seasonal prevalence of Shiga toxin-producing Escherichia coli, including O157:H7 and non-O157 serotypes, and Salmonella in commercial beef processing plants

The seasonal prevalence of Escherichia coli O157:H7, Salmonella, non-O157 E. coli (STEC), and stx-harboring cells was monitored at three Midwestern fed-beef processing plants. Overall, E. coli O157:H7 was recovered from 5.9% of fecal samples, 60.6% of hide samples, and 26.7% of carcasses sampled before the preevisceration wash. This pathogen also was recovered from 1.2% (15 of 1,232) of carcasses sampled at chilling (postintervention) at approximate levels of <3.0 cells per 100 cm2. In one case, the E. coli O157:H7 concentration dropped from ca. 1,100 cells per 320 cm2 at the preevisceration stage to a level that was undetectable on ca. 2,500 cm2 at the postintervention stage. The prevalence of E. coli O157:H7 in feces peaked in the summer, whereas its prevalence on hide was high from the spring through the fall. Overall, Salmonella was recovered from 4.4, 71.0, and 12.7% of fecal, hide, and preevisceration carcass samples, respectively. Salmonella was recovered from one postintervention carcass (of 1,016 sampled). Salmonella prevalence peaked in feces in the summer and was highest on hide and preevisceration carcasses in the summer and the fall. Non-O157 STEC prevalence also appeared to vary by season, but the efficiency in the recovery of isolates from stx-positive samples ranged from 37.5 to 83.8% and could have influenced these results. Cells harboring stx genes were detected by PCR in 34.3, 92.0, 96.6, and 16.2% of fecal, hide, preevisceration carcass, and postintervention carcass samples, respectively. The approximate level of non-O157 STEC and stx-harboring cells on postintervention carcasses was > or = 3.0 cells per 100 cm2 for only 8 of 199 carcasses (4.0%). Overall, the prevalence of E. coli O157:H7, Salmonella, and non-O157 STEC varied by season, was higher on hides than in feces, and decreased dramatically, along with pathogen levels, during processing and during the application of antimicrobial interventions. These results demonstrate the effectiveness of the current interventions used by the industry and highlight the significance of hides as a major source of pathogens on beef carcasses.     

Fate of Shiga toxin-producing O157:H7 and non-O157:H7 Escherichia coli cells within blade-tenderized beef steaks after cooking on a commercial open-flame gas grill

We compared the fate of cells of both Shiga toxin-producing Escherichia coli O157:H7 (ECOH) and Shiga toxin-producing non-O157:H7 E. coli (STEC) in blade-tenderized steaks after tenderization and cooking on a gas grill. In phase I, beef subprimal cuts were inoculated on the lean side with about 5.5 log CFU/g of a five-strain mixture of ECOH or STEC and then passed once through a mechanical blade tenderizer with the lean side facing up. In each of two trials, 10 core samples were removed from each of two tenderized subprimals and cut into six consecutive segments starting from the inoculated side. Ten total cores also were obtained from two nontenderized (control) subprimals, but only segment 1 (the topmost segment) was sampled. The levels of ECOH and STEC recovered from segment 1 were about 6.0 and 5.3 log CFU/g, respectively, for the control subprimals and about 5.7 and 5.0 log CFU/g, respectively, for the tenderized subprimals. However, both ECOH and STEC behaved similarly in terms of translocation, and cells of both pathogen cocktails were recovered from all six segments of the cores obtained from tenderized subprimals, albeit at lower levels in segments 2 to 6 than those found in segment 1. In phase II, steaks (2.54 and 3.81 cm thick) cut from tenderized subprimals were subsequently cooked (three steaks per treatment) on a commercial open-flame gas grill to internal temperatures of 48.9, 54.4, 60.0, 65.6, and 71.1°C. Regardless of temperature or thickness, we observed 2.0- to 4.1-log and 1.5- to 4.5-log reductions in ECOH and STEC levels, respectively. Both ECOH and STEC behaved similarly in response to heat, in that cooking eliminated significant numbers of both pathogen types; however, some survivors were recovered due, presumably, to uneven heating of the blade-tenderized steaks.     

Elimination of Escherichia coli O 157 : H7 and Listeria monocytogenes from raw beef sausage by gamma-irradiation

The effectiveness of low gamma-irradiation doses in the destruction of Escherichia coli O 157 : H7 and Listeria monocytogenes in raw beef sausages was investigated. Raw samples of fresh manufactured beef sausage were subjected to gamma-irradiation at doses of 0, 1, 2, and 3 kGy. Then samples were cold-stored (4 +/- 1 degrees C) for 12 days and the effects of irradiation and storage on the counts of these harmful bacteria were studied. Moreover, the effects of irradiation and storage on the percentages of free fatty acids (FFAs) in lipids, on the p-anisidine values of lipids, solubility of sarcoplasmic and myofibrilar proteins, and water-holding capacity (WHC) were also determined. The results showed that gamma-irradiation at 1 and 2 kGy significantly reduced the counts of E. coli O 157 : H7 and L. monocytogenes, while 3 kGy dose effectively eliminated these bacteria by more than 4 log and 3 log units, respectively, and could keep their counts below the detection level during storage. Gamma-irradiation had no significant effects on the percentages of FFAs in lipids, solubility of sarcoplasmic and myofibrilar proteins, and WHC of samples, while it significantly increased the p-anisidine value of lipids. During storage, significant increases in the percentages of FFAs and p-anisidine values were observed for lipids of irradiated and nonirradiated sausages, while the solubility of sarcoplasmic and myofibrilar proteins showed no significant changes. Moreover, samples of irradiated and nonirradiated sausages showed significant decreases in their WHC during the first 6 days of storage at 4 +/- 1 degrees C, then showed no significant changes. Finally, gamma-irradiation at a dose of 3 kGy appeared to be sufficient to improve the microbiological safety of raw beef sausages without adverse effects on their chemical properties.     

Immunoconcentration of Shiga toxin-producing Escherichia coli O157 from animal faeces and raw meats by using Dynabeads anti-E. coli O157 and the VIDAS system

To identify the reservoirs and routes of transmission of Shiga toxin-producing Escherichia coli (STEC) O157, sensitive detection and isolation methods are necessary. The sensitivity of traditional culture methods can be improved significantly by the inclusion of an immunoconcentration step, resulting in less false-negatives. In this report, we evaluated the results of two commercially available test systems: Dynabeads anti-E. coli O157 and the Vitek Immunodiagnostic Assay System (VIDAS) Immuno-Concentration E. coli O157 (ICE) kit. Additionally, we compared two selective isolation media for STEC O157. Statistical analysis of the results obtained for animal faecal samples (n=637) examined by both immunoconcentration methods showed that by the manual Dynabeads anti-E. coli O157 procedure systematically more samples were identified as positive than by the VIDAS ICE. In case of meat samples (n=360), no difference between the results of the two methods was found. In addition to being accurate, the Dynabeads anti-E. coli O157 method is a less expensive method than the VIDAS ICE. But, the Dynabeads method is laborious and there is a risk of cross-contamination. The VIDAS ICE procedure on the other hand is fully automated with a standardised performance; fast and safe for the user. Irrespective of the type of sample (faeces or meat) and the immunoconcentration technique applied (Dynabeads anti-E. coli O157 or VIDAS ICE) more samples were found positive after plating onto CHROMagar O157 with cefixime (0.025 mg l(-1)) and tellurite (1.25 mg l(-1)) than after plating onto sorbitol-MacConkey agar with cefixime (0.05 mg l(-1)) and tellurite (2.5 mg l(-1)). However, only in case of meat samples examined by the VIDAS ICE the difference between the isolation media was not statistically significant.     

大肠杆菌O157的志贺毒素基因克隆和测序

将一株大肠杆菌O157PCR扩增stx2基因全长并克隆测序。该菌株stx2基因与GenBank数据库收录的stx2基因最高同源性为98%,在3个核苷酸位点存在基因突变。采用邻位相连法构建进化树,序列分析结果表明O157为stx2C基因亚型。了解大肠杆菌O157的基因突变情况,并为开发大肠杆菌分子检测方法提供了参考。     

Shiga toxin-producing Escherichia coli in healthy young beef steers from Argentina: prevalence and virulence properties

Between July 1999 and December 2000, the prevalence of Shiga toxin-producing Escherichia coli (STEC) was established in 200 Argentine healthy young beef steers (14-16 months old) grown under local production systems with a feed grain period of 3-4 months, and the STEC strains isolated were examined in regard to their phenotypic and genotypic characteristics. Stool samples (n = 70) and rectal swabs (n = 130) were taken at the slaughterhouse level. By polymerase chain reaction (PCR), Shiga toxin (stx) gene sequences were detected in 69% of the samples. Eighty-six STEC strains were isolated from 39% of the animals. Serogroups identified, in order of frequency, were: O8 (16 strains), O113 (14), O103 (5), O91 (4), O171 (3), O174 (3), O25 (2), O112 (2), O145 (2), O2, O11, O104, O121, O128, O143, O146, O157. The most frequent serotype isolated was O8:H19 (12.9%). A total of 17 serotypes, including E. coli O157:H7 found in one animal (0.5%), have been previously associated with hemolytic uremic syndrome (HUS), bloody and non-bloody diarrhea in different countries, including Argentina. The prevalent genotype isolated was stx2 (51 of 86, 59.3%). Subtyping of stx2 variants showed the prevalence of stx2vh-b (25.6%) and stx2vh-a types (24.4%), and revealed the presence of an atypical stx2-v. Only 7.0% of STEC strains carried eae, and 33.7% harbored EHEC-hlyA gene. The full virulent genotype (stx/eae/EHEC-hlyA) was found to be present in 4 of the 86 (4.7%) STEC strains isolated. This research indicates that young steers from the main beef-producing area of Argentina are an important reservoir of STEC strains; however, its importance as agents of human diseases in our country has still to be established.     

Behavior of Escherichia coli O157:H7 in leafy vegetables

Leafy vegetables, including lettuce and spinach, have been implicated in several outbreaks of foodborne disease caused by Escherichia coli O157:H7, a pathogen of increasing public health significance because of the severity of the gastrointestinal illness and long-term, chronic sequelae that can result from infection. A definitive association between the consumption of leafy vegetables and human disease provides implicit evidence of transfer from animal sources to field crops and retail commodities, including minimally processed or fresh-cut products. Understanding the behavior of E. coli O157:H7 in leafy vegetables during production, after harvest, in storage, during processing, and in packaged fresh-cut products is essential for the development of effective control measures. To this end, previous research on the fate of the species at each step in the production of market-ready leafy vegetables is reviewed in this study. Several critical gaps in knowledge are identified, notably uncertainty about the location of contaminating cells on or in plant tissues, behavior in packaged products stored at low temperatures, and the influence of environmental stresses on growth and infectivity.     

Carvacrol and cinnamaldehyde facilitate thermal destruction of Escherichia coli O157:H7 in raw ground beef

The heat resistance of a four-strain mixture of Escherichia coli O157:H7 in raw ground beef in both the absence and presence of the antimicrobials carvacrol and cinnamaldehyde was tested at temperatures ranging from 55 to 62.5 degrees C. Inoculated meat packaged in bags was completely immersed in a circulating water bath, cooked for 1 h to an internal temperature of 55, 58, 60, or 62.5 degrees C, and then held for predetermined lengths of time ranging from 210 min at 55 degrees C to 5 min at 62.5 degrees C. The surviving bacteria were enumerated by spiral plating onto tryptic soy agar overlaid with sorbitol MacConkey agar. Inactivation kinetics of the pathogens deviated from first-order kinetics. D-values (time for the bacteria to decrease by 90%) in the control beef ranged from 63.90 min at 55 degrees C to 1.79 min at 62.5 degrees C. D-values determined by a logistic model ranged from 43.18 min (D1, the D-value of a major population of surviving cells) and 89.84 min (D2, the D-value of a minor subpopulation) at 55 degrees C to 1.77 (D1) and 0.78 min (D2) at 62.5 degrees C. The thermal death times suggested that to achieve a 4-D reduction, contaminated processed ground beef should be heated to an internal temperature of 60 degrees C for at least 30.32 min. Significantly increased sensitivity to heat (P < 0.05) was observed with the addition and/or increasing levels of carvacrol or cinnamaldehyde from 0.5 to 1.0%. The observed thermal death times may facilitate the design of acceptance limits at critical control points for ground beef at lower times and temperatures of heating.     

Escherichia coli O157 and non-O157 Shiga toxin-producing Escherichia coli in fecal samples of finished pigs at slaughter in Switzerland

Fecal samples from 630 slaughtered finisher pigs were examined by PCR to assess the shedding of Escherichia coli O157 (rfbE) and Shiga toxin-producing E. coli (STEC, stx). The proportion of positive samples was 7.5% for rfbE and 22% for stx. By colony hybridization, 31 E. coli O157 and 45 STEC strains were isolated, and these strains were further characterized by phenotypic and genotypic traits. Among E. coli O157 strains, 30 were sorbitol positive, 30 had an H type other than H7, and none harbored stx genes. Intimin (eae), enterohemolysin (ehxA), EAST1 (astA), and porcine A/E-associated protein (paa) were present in 10, 3, 26, and 6% of strains. Among them, one eae-gamma1-positive O157:H7 strain testing positive for ehxA and astA and two eae-alpha1-positive O157:H45 strains were classified as enteropathogenic E. coli (EPEC). The O157:H45 EPEC harbored the EAF plasmid and the bfpA gene, factors characteristic for typical EPEC. The isolated STEC strains (43 sorbitol positive) belonged to 11 O:H serotypes, including three previously reported in human STEC causing hemolytic uremic syndrome (O9:H-, O26:H-, and O103:H2). All but one strain harbored stx2e. The eae and ehxA genes, which are strongly correlated with human disease, were present in only one O103:H2 strain positive for stx1 and paa, whereas the astA gene was found more frequently (14 strains). High prevalence of STEC was found among finisher pigs, but according to the virulence factors the majority of these strains seem to be of low virulence.     

原料乳中大肠杆菌O157:H7的快速检测

建立了一种快速检测原料乳中大肠杆菌O157:H7的PCR技术.该方法利用过滤富集菌体后的PCR技术来检测原料乳中大肠杆菌O157:H7,先对人工污染大肠杆菌O157:H7的原料乳进行离心脱脂,然后添加EDTA-2Na获得澄清乳液,最后通过0.45 μm微膜过滤收集菌体,整个过程只需6 h左右即可完成.检测灵敏度高达10-mL-1.这种方法在传统检测方法的基础上做了有效改进,使得原料乳中的大肠杆菌O157:H7的检测能够快速、准确、灵敏的进行.     

Prevalence, serotypes and virulence genes of Shiga toxin-producing Escherichia coli isolated from ovine and caprine milk and other dairy products in Spain

The aim of this study was to determinate the prevalence, serotypes and virulence genes of Shiga toxin-producing Escherichia coli (STEC) strains isolated from different dairy products (DP) in Spain with the purpose of determining whether DP represent a potential source of STEC pathogenic for humans. A total of 502 DP were examined from 64 different ovine and caprine flocks and 6 dairy plants in Extremadura (Western Spain). Samples were collected monthly between March 2003 and June 2004 and included 360 unpasteurised milk obtained from the bulk tank, 103 fresh cheese curds and 39 cheeses. Samples obtained were examined for STEC using genotypic (PCR) methods. STEC strains were detected from 39 (10.8%) bulk tank, 4 (3.9%) fresh cheese curds and 2 (5%) cheese, whereas O157:H7 serotype were isolated from one (0.3%) bulk tank. A total of 9 STEC strains (O27:H18, O45:H38, O76:H19, O91:H28, O157:H7, ONT:H7, ONT:H9 and ONT:H21) were identified in this study. One of them, the serotype O27:H18, has not been reported previously as STEC. PCR showed that 3 strains carried stx1 genes, 5 possessed stx2 genes and 1 both stx1 and stx2. Whereas all STEC caprine isolates showed ehxA genes, only O157:H7 serotype showed eae virulence genes. The strain O157:H7 isolated possessed intimin type gamma1 and belonged to phage type 31. This study confirms that dairy product is an important reservoir of STEC pathogenic for humans.     

Effect of preservatives on Shiga toxigenic phages and Shiga toxin of Escherichia coli O157:H7

Toxin synthesis by Shiga toxin-producing Escherichia coli (STEC) appears to be coregulated through the induction of the integrated bacteriophages that encode the toxin genes. These phages might be the principal means for the dissemination and release of Shiga toxins. We evaluated the effect of three common food preservatives, potassium sorbate, sodium benzoate, and sodium propionate, on the propagation of the phages and Shiga toxins. We tested each preservative at four concentrations, 1, 1.25, 2.5, and 5 mg/ml, both on free phages and on lysogenic phages in bacteria. We also evaluated the expression of a lambdoid phage, which was exposed to increasing concentrations of preservatives, by measuring β-galactosidase activity from SPC105, a transductant strain. Furthermore, we tested the effect of the preservatives on cytotoxigenic activity of Shiga toxin on Vero cells. We detected an increase of the inhibitory effect of the phage lytic activity, both in lysogenic and free phages, as the preservative concentration increased. However, the inhibition was higher on the lysogenic phages release than on free phages. Sodium benzoate and potassium sorbate were about equal at inhibiting phages; they were more effective than sodium propionate. A significant decrease of lacZ expression, encoded in a lambda phage, was observed. We also found a reduction in Shiga toxin titer caused by exposure of E. coli O157:H7 to 5 mg/ml sodium benzoate or potassium sorbate. These results imply that these three preservatives, used to inhibit microbial spoilage of foods, also act to inhibit lytic activity and dispersion of a phage carrying the gene encoding powerful Shiga cytotoxins. Also notable was the inactivation of Shiga toxin activity, although this effect was detected using concentrations of preservatives greater than those allowed by the Argentine Food Code.     

Escherichia coli O157:H7 shedding in vaccinated beef calves born to cows vaccinated prepartum with Escherichia coli O157:H7 SRP vaccine

Extensive research, intervention equipment, money, and media coverage have been directed at controlling Escherichia coli O157:H7 in beef cattle. However, much of the focus has been on controlling this pathogen postcolonization. This study was conducted to examine the performance, health, and shedding characteristics of beef calves that were vaccinated with an E. coli O157:H7 SRP bacterial extract. These calves had been born to cows vaccinated prepartum with the same vaccine. Cows and calves were assigned randomly to one of four treatments: (i) neither cows nor calves vaccinated with E. coli O157:H7 SRP (CON), (ii) cows vaccinated with E. coli O157:H7 SRP prepartum but calves not vaccinated (COWVAC), (iii) calves vaccinated with E. coli O157:H7 SRP but born to cows not vaccinated (CALFVAC), (iv) cows vaccinated with E. coli O157:H7 SRP prepartum and calves also vaccinated (BOTH). Calves born to vaccinated cows had significantly higher titers of anti-E. coli O157:H7 SRP antibodies (SRPAb) in circulation at branding time (P < 0.001). Upon entry to the feedlot, overall fecal E. coli O157:H7 prevalence was 23 % among calves, with 25 % in the CON treatment group, 19 % in the CALFVAC group, 32 % in the COWVAC group, and 15 % in the BOTH group (P > 0.05). Fecal shedding of E. coli O157 on arrival to the feedlot was not correlated with fecal shedding at slaughter (Spearman's rho = -0.02; P = 0.91). No significant effects of cow or calf E. coli O157:H7 SRP vaccination treatment were found on feedlot calf health or performance (P > 0.05), prevalence of lung lesions or liver abscess (P > 0.05), or morbidity, retreatment, or mortality numbers (P > 0.05). The findings of this study indicate that the timing of vaccination of calves against E. coli O157:H7 may be an important consideration for maximizing the field efficacy of this vaccine.