Reduction of Escherichia coli O157:H7 populations in cattle by addition of colicin E7-producing E. coli to feed

A cattle trial using artificially inoculated calves was conducted to determine the effect of the addition of colicinogenic Escherichia coli strains capable of producing colicin E7 (a 61-kDa DNase) to feed on the fecal shedding of serotype O157:H7. The experiment was divided into three periods. In period 1, which lasted 24 days, six calves were used as controls, and eight calves received 10(7) CFU of E. coli (a mixture of eight colicinogenic E. coli strains) per g of feed. Both groups were orally inoculated with nalidixic acid-resistant E. coli O157:H7 strains 7 days after the treatment started. In periods 2 and 3, the treatment and control groups were switched, and the colicinogenic E. coli dose was increased 10-fold. During period 3, which lasted as long as period 1, both groups were reinoculated with E. coli O157:H7. The numbers of E. coli O157:H7 were consistently greater in the control groups during the three periods, but comparisons within each time period determined a statistically significant (P < 0.05) difference only at day 21 of period 1. However, when the daily average counts were compared between the period 1 control group and the period 3 treatment group that included the same six animals, an overall reduction of 1.1 log(10) CFU/g was observed, with a maximum decrease of 1.8 log(10) CFU/g at day 21 (overall statistical significance, P = 0.001). Serotype O157:H7 was detected in 44% of the treatment group's intestinal tissue samples and in 64% of those from the control group (P < 0.04). These results indicated that the daily addition of 10(8) CFU of colicin E7-producing E. coli per gram of feed could reduce the fecal shedding of serotype O157:H7.     

Shedding of Escherichia coli O157:H7 in dairy cattle housed in a confined environment following waterborne inoculation

A study of Escherichia coli O157:H7 transmission and shedding was conducted with bull calves housed in individual pens within a confined environment. For comparative purposes, the numbers and duration of E. coli O157:H7 shedding in naturally infected calves were monitored after a single purchased calf (calf 156) tested positive prior to inoculation. During the next 8 days, the calves in adjacent pens and a pen directly across a walkway from calf 156 began to shed this serotype O157:H7 strain. Five of the eight calves in this room shed this O157:H7 strain at some time during the following 8 weeks. The numbers of E. coli O157:H7 isolates shed in these calves varied from 60 to 10(5) CFU/g of feces, and the duration of shedding ranged from 17 to >31 days. The genomic DNAs from isolates recovered from these calves were indistinguishable when compared by using XbaI digestion and pulsed-field gel electrophoresis. Inoculation of calves with 1 liter of water containing ca. 10(3) to 10(4) CFU of E. coli O157:H7/ml resulted in shedding in 10 of 12 calves (trial 1, 4 of 4 calves; trial 2, 6 of 8 calves). The inoculated calves shed the inoculation strain (FRIK 1275) as early as 24 h after administration. The duration of shedding varied from 18 to >43 days at levels from 10(2) to 10(6) CFU/g of feces. The numbers of doses necessary to initiate shedding varied among calves, and two calves in trial 2 never shed FRIK 1275 after four doses (ca. 10(6) CFU per dose). Results from this study confirm previous reports of animal-to-animal and waterborne dissemination of E. coli O157:H7 and highlight the need for an effective water treatment to reduce the spread of this pathogen in cattle.     

Experimental and field studies of Escherichia coli O157:H7 in white-tailed deer

Studies were conducted to evaluate fecal shedding of Escherichia coli O157:H7 in a small group of inoculated deer, determine the prevalence of the bacterium in free-ranging white-tailed deer, and elucidate relationships between E. coli O157:H7 in wild deer and domestic cattle at the same site. Six young, white-tailed deer were orally administered 10(8) CFU of E. coli O157:H7. Inoculated deer were shedding E. coli O157:H7 by 1 day postinoculation (DPI) and continued to shed decreasing numbers of the bacteria throughout the 26-day trial. Horizontal transmission to an uninoculated deer was demonstrated. Although E. coli O157:H7 bacteria were recovered from the gastrointestinal tracts of deer necropsied from 4 to 26 DPI, attaching and effacing lesions were not apparent in any deer. Results are similar to those of inoculation studies in calves and sheep. In field studies, E. coli O157 was not detected in 310 fresh deer fecal samples collected from the ground. It was detected in feces, but not in meat, from 3 of 469 free-ranging deer in 1997. In 1998, E. coli O157 was not detected in 140 deer at the single positive site found in 1997; however, it was recovered from 13 of 305 dairy and beef cattle at the same location. Isolates of E. coli O157:H7 from deer and cattle at this site differed with respect to pulsed-field gel electrophoresis patterns and genes encoding Shiga toxins. The low overall prevalence of E. coli O157:H7 and the identification of only one site with positive deer suggest that wild deer are not a major reservoir of E. coli O157:H7 in the southeastern United States. However, there may be individual locations where deer sporadically harbor the bacterium, and venison should be handled with the same precautions recommended for beef, pork, and poultry.     

Experimental Escherichia coli O157:H7 carriage in calves.

Nine weaned calves (6 to 8 weeks of age) were given 10(10) CFU of a five-strain mixture of enterohemorrhagic Escherichia coli O157:H7 by oral-gastric intubation. After an initial brief period of pyrexia in three calves and transient mild diarrhea in five calves, calves were clinically normal throughout the 13- to 27-day study. The population of E. coli O157:H7 in the faces decreased dramatically in all calves during the first 2 weeks after inoculation. Thereafter, small populations of E. coli O157:H7 persisted in all calves, where they were detected intermittently in the feces and rumen contents. While withholding food increased fecal shedding of E. coli O157:H7 by 1 to 2 log10/g in three of four calves previously shedding small populations of E. coli O157:H7, the effect of fasting on fecal shedding of E. coli O157:H7 was variable in calves shedding larger populations. At necropsy, E. coli O157:H7 was not isolated from sites outside the alimentary tract. E. coli O157:H7 was isolated from the forestomach or colon of all calves at necropsy. Greater numbers of E. coli O157:H7 were present in the gastrointestinal contents than in the corresponding mucosal sections, and there was no histologic or immunohistochemical evidence of E. coli O157:H7 adhering to the mucosa. In conclusion, under these experimental conditions, E. coli O157:H7 is not pathogenic in weaned calves, and while it does not appear to colonize mucosal surfaces for extended periods, E. coli O157:H7 persists in the contents of the rumen and colon as a source for fecal shedding.     

Shedding of Escherichia coli O157:H7 in Dairy Cattle Housed in a Confined Environment following Waterborne Inoculation

A study of Escherichia coli O157:H7 transmission and shedding was conducted with bull calves housed in individual pens within a confined environment. For comparative purposes, the numbers and duration of E. coli O157:H7 shedding in naturally infected calves were monitored after a single purchased calf (calf 156) tested positive prior to inoculation. During the next 8 days, the calves in adjacent pens and a pen directly across a walkway from calf 156 began to shed this serotype O157:H7 strain. Five of the eight calves in this room shed this O157:H7 strain at some time during the following 8 weeks. The numbers of E. coli O157:H7 isolates shed in these calves varied from 60 to 10⁵ CFU/g of feces, and the duration of shedding ranged from 17 to >31 days. The genomic DNAs from isolates recovered from these calves were indistinguishable when compared by using XbaI digestion and pulsed-field gel electrophoresis. Inoculation of calves with 1 liter of water containing ca. 10³ to 10⁴ CFU of E. coli O157:H7/ml resulted in shedding in 10 of 12 calves (trial 1, 4 of 4 calves; trial 2, 6 of 8 calves). The inoculated calves shed the inoculation strain (FRIK 1275) as early as 24 h after administration. The duration of shedding varied from 18 to >43 days at levels from 10² to 10⁶ CFU/g of feces. The numbers of doses necessary to initiate shedding varied among calves, and two calves in trial 2 never shed FRIK 1275 after four doses (ca. 10⁶ CFU per dose). Results from this study confirm previous reports of animal-to-animal and waterborne dissemination of E. coli O157:H7 and highlight the need for an effective water treatment to reduce the spread of this pathogen in cattle.     

Gastrointestinal tract location of Escherichia coli O157:H7 in ruminants

Experimentally inoculated sheep and cattle were used as models of natural ruminant infection to investigate the pattern of Escherichia coli O157:H7 shedding and gastrointestinal tract (GIT) location. Eighteen forage-fed cattle were orally inoculated with E. coli O157:H7, and fecal samples were cultured for the bacteria. Three distinct patterns of shedding were observed: 1 month, 1 week, and 2 months or more. Similar patterns were confirmed among 29 forage-fed sheep and four cannulated steers. To identify the GIT location of E. coli O157:H7, sheep were sacrificed at weekly intervals postinoculation and tissue and digesta cultures were taken from the rumen, abomasum, duodenum, lower ileum, cecum, ascending colon, descending colon, and rectum. E. coli O157:H7 was most prevalent in the lower GIT digesta, specifically the cecum, colon, and feces. The bacteria were only inconsistently cultured from tissue samples and only during the first week postinoculation. These results were supported in studies of four Angus steers with cannulae inserted into both the rumen and duodenum. After the steers were inoculated, ruminal, duodenal, and fecal samples were cultured periodically over the course of the infection. The predominant location of E. coli O157:H7 persistence was the lower GIT. E. coli O157:H7 was rarely cultured from the rumen or duodenum after the first week postinoculation, and this did not predict if animals went on to shed the bacteria for 1 week or 1 month. These findings suggest the colon as the site for E. coli O157:H7 persistence and proliferation in mature ruminant animals.     

Role of rpoS in acid resistance and fecal shedding of Escherichia coli O157:H7

Acid resistance (AR) is important to survival of Escherichia coli O157:H7 in acidic foods and may play a role during passage through the bovine host. In this study, we examined the role in AR of the rpoS-encoded global stress response regulator sigma(S) and its effect on shedding of E. coli O157:H7 in mice and calves. When assayed for each of the three AR systems identified in E. coli, an rpoS mutant (rpoS::pRR10) of E. coli O157:H7 lacked the glucose-repressed system and possessed reduced levels of both the arginine- and glutamate-dependent AR systems. After administration of the rpoS mutant and the wild-type strain (ATCC 43895) to ICR mice at doses ranging from 10(1) to 10(4) CFU, we found the wild-type strain in feces of mice given lower doses (10(2) versus 10(3) CFU) and at a greater frequency (80% versus 13%) than the mutant strain. The reduction in passage of the rpoS mutant was due to decreased AR, as administration of the mutant in 0.05 M phosphate buffer facilitated passage and increased the frequency of recovery in feces from 27 to 67% at a dose of 10(4) CFU. Enumeration of E. coli O157:H7 in feces from calves inoculated with an equal mixture of the wild-type strain and the rpoS mutant demonstrated shedding of the mutant to be 10- to 100-fold lower than wild-type numbers. This difference in shedding between the wild-type strain and the rpoS mutant was statistically significant (P 相似文献   

Effect of diet on the shedding of Escherichia coli O157:H7 in a sheep model.

The purpose of this study was to develop a sheep model to investigate reproduction, transmission, and shedding of Escherichia coli O157:H7 in ruminants. In addition, we investigated the effect of diet change on these parameters. Six groups of twin lambs given oral inoculations of 10(5) or 10(9) CFU of E. coli O157:H7 and their nondosed mothers were monitored for colonization by culture of fecal samples. A modified selective-enrichment protocol that detected E. coli O157:H7 at levels as low as 0.06 CFU per g of ovine feces was developed. Horizontal transmission of infection occurred between the lambs and most of the nondosed mothers. When animals were kept in confinement and given alfalfa pellet feed, lambs receiving the higher dose shed the bacteria sooner and longer than all other animals. However, when the animals were released onto a sagebrush-bunchgrass range, every animal, regardless of its previous status (dosed at one of the inoculum levels tested or nondosed) shed E. coli O157:H7 uniformly. Shedding persisted for 15 days, after which all animals tested negative. E. coli O157:H7 reproduction and transmission and the combined effect of diet change and feed withholding were also investigated in a pilot study with experimentally inoculated rams. Withholding feed induced animals to shed the bacteria either by triggering growth of E. coli O157:H7 present in the intestines or by increasing susceptibility to infection. Introduction of a dietary change with brief starvation caused uniform shedding and clearance of E. coli O157:H7, and all animals then tested negative for the bacteria.(ABSTRACT TRUNCATED AT 250 WORDS)     

Impact of Dexamethasone-Induced Immunosuppression on the Duration and Level of Shedding of Escherichia coli O157:H7 in Calves

The goal of this study was to determine whether immunosuppression plays a role in the level and duration of fecal shedding of Escherichia coli O157. Immunosuppression was induced in calves by administering dexamethasone. Six 1-week-old Holstein bull calves were injected intramuscularly with dexamethasone and orally inoculated with 10⁹ CFU of a mixture of three nalidixic-acid resistant strains of E. coli O157:H7. Five 1-week-old Holstein bull calves that were given the same oral inoculation of E. coli O157:H7, but not the dexamethasone injections, served as controls. All calves were examined daily and fecal samples were collected three times a week for detection and enumeration of the nalidixic-acid resistant E. coli O157. Four weeks after the last calf stopped shedding, all calves were necropsied and samples from the gastrointestinal tract were taken for the detection of the nalidixic-acid resistant E. coli O157. Dexamethasone-injected calves shed at higher levels (P = 0.04) on days 4 and 7 postinoculation, but not thereafter. None of the samples collected at necropsy were positive for E. coli O157. Data from this study suggest that there may be a time-dependent relationship between dexamethasone immunosuppression and the fecal concentration of E. coli O157 but that transient immunosuppression does not appear to prolong shedding of E. coli O157.     

Reduction of Escherichia coli O157:H7 Populations in Cattle by Addition of Colicin E7-Producing E. coli to Feed

A cattle trial using artificially inoculated calves was conducted to determine the effect of the addition of colicinogenic Escherichia coli strains capable of producing colicin E7 (a 61-kDa DNase) to feed on the fecal shedding of serotype O157:H7. The experiment was divided into three periods. In period 1, which lasted 24 days, six calves were used as controls, and eight calves received 10⁷ CFU of E. coli (a mixture of eight colicinogenic E. coli strains) per g of feed. Both groups were orally inoculated with nalidixic acid-resistant E. coli O157:H7 strains 7 days after the treatment started. In periods 2 and 3, the treatment and control groups were switched, and the colicinogenic E. coli dose was increased 10-fold. During period 3, which lasted as long as period 1, both groups were reinoculated with E. coli O157:H7. The numbers of E. coli O157:H7 were consistently greater in the control groups during the three periods, but comparisons within each time period determined a statistically significant (P < 0.05) difference only at day 21 of period 1. However, when the daily average counts were compared between the period 1 control group and the period 3 treatment group that included the same six animals, an overall reduction of 1.1 log₁₀ CFU/g was observed, with a maximum decrease of 1.8 log₁₀ CFU/g at day 21 (overall statistical significance, P = 0.001). Serotype O157:H7 was detected in 44% of the treatment group's intestinal tissue samples and in 64% of those from the control group (P < 0.04). These results indicated that the daily addition of 10⁸ CFU of colicin E7-producing E. coli per gram of feed could reduce the fecal shedding of serotype O157:H7.     

Persistence and metabolic activity of Escherichia coli O157:H7 in farm animal faeces

Ruminants, and to a lesser extent monogastric farm animals, are known to be natural reservoirs of Escherichia coli O157:H7, and contact with contaminated faeces has been linked to human infection. This study used a nontoxigenic, chromosomally marked, lux reporter strain to compare the persistence and activity (bioluminescence) of E. coli O157:H7 over 21 days in the faecal liquor of five farm animals: horse, sheep, cow, pig and piglet. Samples were inoculated with the lux E. coli O157:H7 (7.82 log CFU mL(-1)) and stored at 20 +/- 1 degrees C. The organism was recovered from all samples throughout the experimental period, although lower numbers were recovered from horse faecal liquor relative to all other types (P<0.001). The organisms' activity declined in all samples over time and no luminescence could be detected in any sample 21 days postinoculation. However, activity did increase greatly within pig and piglet faeces during initial stages of monitoring and overall luminescence was greater in piglet samples compared with all other samples (P<0.001). This is the first study to demonstrate how both the persistence and metabolic activity of E. coli O157:H7 notably varies within a range of ruminant and nonruminant animal faeces. Further research is needed to elucidate the factors that govern differential persistence and metabolic activity of E. coli O157:H7 within such matrices.     

Effect of Dietary Stress on Fecal Shedding of Escherichia coli O157:H7 in Calves

Two groups of calves were subjected to dietary stress by withholding of food beginning 1 or 14 days after inoculation with 10¹⁰ CFU of Escherichia coli O157:H7. Following treatment, neither group had a significant increase in fecal shedding of E. coli O157:H7. A third group of calves had food withheld for 48 h prior to inoculation with 10⁷ CFU of E. coli O157:H7. These calves were more susceptible to infection and shed significantly more E. coli O157:H7 organisms than calves maintained on a normal diet.     

Persistent colonization of sheep by Escherichia coli O157:H7 and other E. coli pathotypes

Shiga toxin-producing Escherichia coli (STEC) is an important cause of food-borne illness in humans. Ruminants appear to be more frequently colonized by STEC than are other animals, but the reason(s) for this is unknown. We compared the frequency, magnitude, duration, and transmissibility of colonization of sheep by E. coli O157:H7 to that by other pathotypes of E. coli. Young adult sheep were simultaneously inoculated with a cocktail consisting of two strains of E. coli O157:H7, two strains of enterotoxigenic E. coli (ETEC), and one strain of enteropathogenic E. coli. Both STEC strains and ETEC 2041 were given at either 10(7) or 10(10) CFU/strain/animal. The other strains were given only at 10(10) CFU/strain. We found no consistent differences among pathotypes in the frequency, magnitude, and transmissibility of colonization. However, the STEC strains tended to persist to 2 weeks and 2 months postinoculation more frequently than did the other pathotypes. The tendency for persistence of the STEC strains was apparent following an inoculation dose of either 10(7) or 10(10) CFU. One of the ETEC strains also persisted when inoculated at 10(10) CFU. However, in contrast to the STEC strains, it did not persist when inoculated at 10(7) CFU. These results support the hypothesis that STEC is better adapted to persist in the alimentary tracts of sheep than are other pathotypes of E. coli.     

Colonization, persistence, and tissue tropism of Escherichia coli O26 in conventionally reared weaned lambs

Escherichia coli O26 is recognized as an emerging pathogen associated with disease in both ruminants and humans. Compared to those of E. coli O157:H7, the shedding pattern and location of E. coli O26 in the gastrointestinal tract (GIT) of ruminants are poorly understood. In the studies reported here, an stx-negative E. coli O26 strain of ovine origin was inoculated orally into 6-week-old lambs and the shedding pattern of the O26 strain was monitored by serial bacteriological examination of feces. The location of colonization in the GIT was examined at necropsy at two time points. The numbers of O26 organisms excreted in feces declined from approximately 10(7) to 10(4) CFU per gram of feces by day 7 and continued at this level for a further 3 weeks. Beyond day 30, excretion was from few animals, intermittent, and just above the detection limit. By day 38, all fecal samples were negative, but at necropsy, O26 organisms were recovered from the upper GIT, specifically the ileum. However, no attaching-effacing (AE) lesions were observed. To identify the location of E. coli O26 within the GIT early after inoculation, two lambs were examined postmortem, 4 days postinoculation. High numbers of O26 organisms were recovered from all GIT sites examined, and approximately 10(9) CFU were recovered from 1 gram of ileal tissue from one animal. Despite high numbers of O26 organisms, AE lesions were identified on the mucosa of the ascending colon of only one animal. These data indicate that E. coli O26 readily colonizes 6-week-old lambs, but the sparseness of AE lesions suggests that O26 is well adapted to this host, and mechanisms other than those dependent upon intimin may play a role in persistence.     

Prevalence of enterohemorrhagic Escherichia coli O157:H7 in a survey of dairy herds.

The prevalence of Escherichia coli O157:H7 in dairy herds is poorly understood, even though young dairy animals have been reported to be a host. From February to May 1993, 662 fecal samples from 50 control herds in 14 states, and from June to August 1993, 303 fecal samples from 14 case herds in 11 states were collected for isolation of E. coli O157:H7. Case herds were those in which E. coli O157:H7 was isolated from preweaned calves in a previous U.S. Department of Agriculture study, whereas control herds from which E. coli O157:H7 had not been isolated previously were randomly selected from the same states as case herds. Among the control herds, E. coli O157:H7 was isolated from 6 of 399 calves (1.5%) that were between 24 h old and the age of weaning and from 13 of 263 calves (4.9%) that were between the ages of weaning and 4 months. Eleven of 50 control herds (22%) were positive. Among the case herds, E. coli O157:H7 was isolated from 5 of 171 calves (2.9%) that were between 24 h old and the age of weaning and from 7 of 132 calves (5.3%) that were between the ages of weaning and 4 months. Seven of 14 case herds (50%) were positive. Sixteen of 31 isolates were obtained by direct plating, with populations ranging from 10(3) to 10(5) CFU/g. Fifteen of 31 isolates were isolated by enrichment only. Nineteen of the isolates produced both verocytotoxin 1 (VT-1) and VT-2, whereas 12 produced VT-2 only.     

Effects of common forage phenolic acids on Escherichia coli O157:H7 viability in bovine feces

Ruminant animals are carriers of Escherichia coli O157:H7, and the transmission of E. coli O157:H7 from cattle to the environment and to humans is a concern. It is unclear if diet can influence the survivability of E. coli O157:H7 in the gastrointestinal system or in feces in the environment. Feces from cattle fed bromegrass hay or corn silage diets were inoculated with E. coli O157:H7, and the survival of this pathogen was analyzed. When animals consumed bromegrass hay for <1 month, viable E. coli O157:H7 was not recovered after 28 days postinoculation, but when animals consumed the diet for >1 month, E. coli O157:H7 cells were recovered for >120 days. Viable E. coli O157:H7 cells in feces from animals fed corn silage were detected until day 45 and differed little with the time on the diet. To determine if forage phenolic acids affected the viability of E. coli O157:H7, feces from animals fed corn silage or cracked corn were amended with common forage phenolic acids. When 0.5% trans-cinnamic acid or 0.5% para-coumaric acid was added to feces from silage-fed animals, the E. coli O157:H7 death rate was increased significantly (17-fold and 23-fold, respectively) compared to that with no addition. In feces from animals fed cracked corn, E. coli O157:H7 death rates were increased significantly with the addition of 0.1% and 0.5% trans-cinnamic acid (7- and 13-fold), 0.1% and 0.5% p-coumaric acid (3- and 8-fold), and 0.5% ferulic acid (3-fold). These data suggest that phenolic acids common to forage plants can decrease viable counts of E. coli O157:H7 shed in feces.     

Early Attachment Sites for Shiga-Toxigenic Escherichia coli O157:H7 in Experimentally Inoculated Weaned Calves

Weaned 3- to 4-month-old calves were fasted for 48 h, inoculated with 10¹⁰ CFU of Shiga toxin-positive Escherichia coli (STEC) O157:H7 strain 86-24 (STEC O157) or STEC O91:H21 strain B2F1 (STEC O91), Shiga toxin-negative E. coli O157:H7 strain 87-23 (Stx⁻ O157), or a nonpathogenic control E. coli strain, necropsied 4 days postinoculation, and examined bacteriologically and histologically. Some calves were treated with dexamethasone (DEX) for 5 days (3 days before, on the day of, and 1 day after inoculation). STEC O157 bacteria were recovered from feces, intestines, or gall bladders of 74% (40/55) of calves 4 days after they were inoculated with STEC O157. Colon and cecum were sites from which inoculum-type bacteria were most often recovered. Histologic lesions of attaching-and-effacing (A/E) O157⁺ bacteria were observed in 69% (38/55) of the STEC O157-inoculated calves. Rectum, ileocecal valve, and distal colon were sites most likely to contain A/E O157⁺ bacteria. Fecal and intestinal levels of STEC O157 bacteria were significantly higher and A/E O157⁺ bacteria were more common in DEX-treated calves than in nontreated calves inoculated with STEC O157. Fecal STEC O157 levels were significantly higher than Stx⁻ O157, STEC O91, or control E. coli; only STEC O157 cells were recovered from tissues. Identifying the rectum, ileocecal valve, and distal colon as early STEC O157 colonization sites and finding that DEX treatment enhances the susceptibility of weaned calves to STEC O157 colonization will facilitate the identification and evaluation of interventions aimed at reducing STEC O157 infection in cattle.     

Reduction of Escherichia coli O157:H7 shedding in cattle by addition of chitosan microparticles to feed

Enterohemorrhagic Escherichia coli O157:H7 (EHEC) is a significant human pathogen that resides in healthy cattle. It is thought that a reduction in the prevalence and numbers of EHEC in cattle will reduce the load of EHEC entering the food chain. To this end, an intervention strategy involving the addition of chitosan microparticles (CM) to feed in order to reduce the carriage of this pathogen in cattle was evaluated. Experiments with individual Holstein calves and a crossover study found that the addition of CM to feed decreased E. coli O157:H7 shedding. In the crossover study, CM resulted in statistically significant reductions in the numbers recovered from rectal swab samples (P < 0.05) and the duration of shedding (P < 0.05). The effects of feeding CM to calves differed, indicating that the optimal levels of CM may differ between animals or that other factors are involved in the interaction between CM and E. coli O157:H7. In vitro studies demonstrated that E. coli O157:H7 binds to CM, suggesting that the reduction in shedding may result at least in part from the binding of positively charged CM to negatively charged E. coli cells. Additional studies are needed to determine the impact of CM feeding on animal production, but the results from this study indicate that supplementing feed with CM reduces the shedding of E. coli O157:H7 in cattle.     

Effect of forage or grain diets with or without monensin on ruminal persistence and fecal Escherichia coli O157:H7 in cattle

Twelve ruminally cannulated cattle, adapted to forage or grain diet with or without monensin, were used to investigate the effects of diet and monensin on concentration and duration of ruminal persistence and fecal shedding of E. coli O157:H7. Cattle were ruminally inoculated with a strain of E. coli O157:H7 (10(10) CFU/animal) made resistant to nalidixic acid (Nal(r)). Ruminal and fecal samples were collected for 11 weeks, and then cattle were euthanized and necropsied and digesta from different gut locations were collected. Samples were cultured for detection and enumeration of Nal(r) E. coli O157:H7. Cattle fed forage diets were culture positive for E. coli O157:H7 in the feces for longer duration (P < 0.05) than cattle fed a grain diet. In forage-fed cattle, the duration they remained culture positive for E. coli O157:H7 was shorter (P < 0.05) when the diet included monensin. Generally, ruminal persistence of Nal(r) E. coli O157:H7 was not affected by diet or monensin. At necropsy, E. coli O157:H7 was detected in cecal and colonic digesta but not from the rumen. Our study showed that cattle fed a forage diet were culture positive longer and with higher numbers than cattle on a grain diet. Monensin supplementation decreased the duration of shedding with forage diet, and the cecum and colon were culture positive for E. coli O157:H7 more often than the rumen of cattle.     

European starlings (Sturnus vulgaris) challenged with Escherichia coli O157 can carry and transmit the human pathogen to cattle

Aims: European starlings (Sturnus vulgaris) are an invasive species in the United States and are considered a nuisance pest to agriculture. The goal of this study was to determine the potential for these birds to be reservoirs and/or vectors for the human pathogen Escherichia coli O157:H7. Materials and Results: Under biosecurity confinement, starlings were challenged with various doses of E. coli O157:H7 to determine a minimum infectious dose, the magnitude and duration of pathogen shedding, and the potential of pathogen transmission among starlings and between starlings and cattle. Birds transiently excreted E. coli O157:H7 following low‐dose inoculation; however, exposure to greater than 10^5.5 colony‐forming units (CFUs) resulted in shedding for more than 3 days in 50% of the birds. Colonized birds typically excreted greater than 10³ CFU g^?1 of faeces, and the pathogen was detected for as long as 14 days postinoculation. Cohabitating E. coli O157:H7‐positive starlings with culture‐negative birds or 12‐week‐old calves resulted in intra‐ and interspecies pathogen transmission within 24 h. Likewise, E. coli O157:H7 was recovered from previously culture‐negative starlings following 24‐h cohabitation with calves shedding E. coli O157:H7. Conclusions: European starlings may be a suitable reservoir and vector of E. coli O157:H7. Significance and Impact of the Study: Given the duration and magnitude of E. coli O157:H7 shedding by European starlings, European starlings should be considered a public health hazard. Measures aimed at controlling environmental contamination with starling excrement, on the farm and in public venues, may decrease food‐producing animal and human exposure to this pathogen.