Prevalence and characterization of Shiga toxin-producing Escherichia coli O157 and O26 in beef farms

Rectal content grab samples were collected from 2436 beef cattle reared on 406 beef farms in Japan between November 2007 and March 2008. STEC strains O157 and O26 were isolated from 110 (27.1%) and 7 (1.7%) farms, respectively. Farms that tested positive for STEC O157 were located in 35 out of all 47 Japanese prefectures. This indicates that STEC O157 strains are widespread on beef farms nationwide. Of the 2436 tested beef cattle, 218 (8.9%) and 10 (0.4%) had STEC strains O157 and O26 in the rectal content, respectively. The most common Shiga toxin genes detected in the isolated STEC O157 strains were: stx(2c) alone (32.1%), stx(2)/stx(2c) (27.2%), and stx(1)/stx(2) (21.8%). Almost all of the STEC O157 and STEC O26 strains expressed Shiga toxins (Stx). Most of the STEC O157 and STEC O26 strains possessed eaeA and EHEC-hlyA. These results strongly suggest that STEC strains O157 and O26 from beef cattle would be pathogenic to humans. Therefore, it is important to reduce STEC strains O157 and O26 in beef cattle in order to prevent foodborne disease caused by STEC. The presence of dogs and/or cats on a farm was significantly (P=0.02) associated with the prevalence of STEC O157. More research is needed to clarify the role of dogs and cats.     

Prevalence estimation and risk factors for Escherichia coli O157 on Dutch dairy farms

To estimate the prevalence of Escherichia coli O157 on Dutch dairy herds, faecal samples were collected once from 678 randomly selected dairy farms in the period October 1996-December 2000. Samples were cultured for E. coli O157. Thirty-eight isolates were tested for virulence genes (eae, VT1 and VT2). A questionnaire about farm characteristics was taken from the farm manager, resulting in variables that could be analysed to identify and quantify factors associated with presence of E. coli O157. In total, 49 of the 678 herds (7.2%) showed at least one positive pooled sample. E. coli O157 was not isolated from herds sampled in December-April in consecutive years (except for one isolate found in March, 2000). VT- and eae-genes were found in 37 and 38 isolates, respectively. Logistic regression was performed on variables obtained from the questionnaire, comparing E. coli O157-positive herds to negative herds. To account for season, a sine function was included in the logistic regression as an offset variable. In the final model, the presence of at least one pig at the farm (OR = 3.4), purchase of animals within the last 2 years before sampling (OR = 1.9), supply of maize (OR = 0.29) to the cows, and sampling a herd in the year 1999 or 2000 (compared to sampling in 1998; OR = 2.1 and 2.9, respectively) had associations with the presence of E. coli O157.     

Alternative sampling to establish the Escherichia coli O157 status on beef cattle farms

Prevalence of Escherichia coli O157 in cattle at the farm level is mostly determined by taking individually rectal samples. From the animal welfare point of view the collection of such samples on the farm is not advisable. The present study evaluated alternative sample types to assess the E. coli O157 status of cattle farms. Twelve closed cattle farms were visited twice with a time interval of 6-8 months. Rectal and hide surface samples (the nose, the neck, the shoulder, the flank, and the round) were collected from beef cattle within the period of 5 months before slaughter and from their environment (overshoes from the pen bedding, swabs from the pen barrier, feed and water). Statistical analysis revealed that from all samples taken only the "overshoe method" might be a good sampling technique to substitute the collection of individual fecal samples to establish the E. coli O157 status of a farm and even a pen. Characterization of the isolates, using pulsed field gel electrophoresis, revealed that on each positive farm only one genotype was presented, even after a period of more than 6 months.     

A preliminary study of Salmonella, verocytotoxigenic Escherichia coli/Escherichia coli O157 and Campylobacter on four mixed farms

The aims of this study were to investigate the incidence of Salmonella, verocytotoxigenic Escherichia coli (VTEC)/Escherichia coli O157 and Campylobacter on four mixed farms and to characterize the isolates in terms of a range of virulence factors. Eighty-nine composite (five different samples from the same animal species combined) faecal [cattle (24), pigs (14), sheep (4), poultry (4), horses (7), deer (4), dogs (9), rodents (2) and wild birds (20)] samples, 16 composite soil samples plus 35 individual water samples were screened using culture-based, immunomagnetic separation and molecular methods. Salmonella was detected in bovine faeces, cattle and poultry house water. Salmonella serotypes/phage types included Dublin, Kiel and Typhimurium DT193, and most isolates were spvC, invA and rck positive. The pefA and rck genes were found exclusively in the non-Typhimurium strains, while Salmonella Dublin and Salmonella Kiel strains carried Salmonella genomic island I marker(s). VTEC/E. coli O157 were found in deer and dog faeces only. The E. coli O157 isolate was an enteroinvasive E. coli, while the VTEC isolate was untypable but carried the vt1, eaeA, hlyA, tir and eptD genes. This article reports the first confirmed carriage of E. coli O157 in Irish deer. Campylobacter species were not detected over the course of this study. It was concluded that [1] Salmonella, VTEC and Campylobacter have low (<5%) prevalence or are absent on the farms in this study; [2] water was an important source of bacterial pathogens; [3] both dogs and deer may act as a source of pathogenic E. coli and [4] key virulence and resistance determinants are widespread in farm Salmonella strains. This study highlights the need to control water as a source of pathogens and suggests that the domestic pets and deer should be considered in any farm risk assessment.     

Escherichia coli O157 in Dutch domesticated rabbits

Enterohaemorrhagic Escherichia coli (EHEC) has been detected in both wild and domesticated rabbits in other countries. The aim of this study was to determine whether the most pathogenic E. coli serotype, O157:H7, occurs in the Dutch domesticated rabbit population and thus could form a public health risk. To this end, faecal samples were collected from rabbits from two rabbit farms and 741 rabbits of different breeds and origin and analysed for E. coli O157:H7, using a combination of enrichment, immunomagnetic separation, selective culture, and PCR. E. coli O157:H7 was not detected in any of the samples. The results indicate that Dutch domesticated rabbits probably do not play a role in the infection of humans with E. coli O157:H7.     

Occurrence of Escherichia coli O157 in Finnish cattle

Bovine faecal samples were collected during June-December 1997 at 14 major abattoirs slaughtering cattle in Finland. Escherichia coli O157 was isolated from 19 of the 1448 samples (1.31%) after enrichment and immunomagnetic separation (IMS). The positive faecal isolates originated from 16 farms and eight abattoirs. The occurrence of E. coli O157 was highest in July (8/204; 3.92%) and September (6/244; 2.46%). No E. coli O157 was detected in November and December, nor from the faecal samples from the northernmost region where cattle density is low. All of the isolates carried the eae gene and showed the enterohaemolytic phenotype. All except one were motile and had the flagella antigen H7. Seventeen of the isolates were positive for stx(2) gene and one carried both the stx(1) and stx(2) genes. Of the 17 isolates with stx genes, 16 were verocytotoxin-positive in a reversed passive latex agglutination test after polymyxin extraction but only eight without extraction. The isolates belonged to 10 different pulsed-field gel electrophoresis (PFGE) patterns. The most common PFGE pattern (1.42) was detected in eight isolates (42.1%). Four PFGE patterns (1.1; 1.6; 1.12; 1.14) were identical with those isolated from humans in Finland, suggesting that at least some human E. coli O157 infections may be of bovine origin.     

Results of a longitudinal study of the prevalence of Escherichia coli O157:H7 on cow-calf farms

OBJECTIVE: To describe the frequency and distribution of Escherichia coli O157:H7 in the feces and environment of cow-calf herds housed on pasture. SAMPLE POPULATION: Fecal and water samples for 10 cow-calf farms in Kansas. PROCEDURE: Fecal and water samples were obtained monthly throughout a 1-year period (3,152 fecal samples from 2,058 cattle; 199 water samples). Escherichia coli O157:H7 in fecal and water samples was determined, using microbial culture. RESULTS: Escherichia coli O157:H7 was detected in 40 of 3,152 (1.3%) fecal samples, and 40 of 2,058 (1.9%) cattle had > or = 1 sample with E coli. Fecal shedding by specific cattle was transient; none of the cattle had E coli in more than 1 sample. Significant differences were not detected in overall prevalence among farms. However, significant differences were detected in prevalence among sample collection dates. Escherichia coli O157:H7 was detected in 3 of 199 (1.5%) water samples. CONCLUSIONS AND CLINICAL RELEVANCE: Implementing control strategies for E coli O157:H7 at all levels of the cattle industry will decrease the risk of this organism entering the human food chain. Devising effective on-farm strategies to control E coli O157:H7 in cow-calf herds will require an understanding of the epidemiologic characteristics of this pathogen.     

Aggregation of animal lactobacilli with O157 enterohemorrhagic Escherichia coli

The effect of selected autoaggregative lactobacilli on enterohemorragic O157 Escherichia coli was studied. A total of 27 Lactobacillus sp. strains were examined for expression of autoaggregation and cell surface hydrophobicity. Autoaggregative isolates were obtained from the crops of chickens and vaginas of calves. Aggregative activity was seen between eight autoaggregative lactobacilli and six strains of enterohemorrhagic E. coli O157. The presence of aggregation-promoting factor (apf gene) was confirmed by polymerase chain reaction (PCR). We propose that autoaggregative lactobacilli that aggregate with enterohemorrhagic E. coli can express a class of APF proteins that exhibit the function of an aggregative mediator. The results of this study suggest that APF-producing lactobacilli could represent a further mechanism in the interaction of comensal microflora with enterohemorrhagic E. coli.     

用PCR鉴定大肠杆菌O157∶H7

根据大肠杆菌Ｏ１５７∶Ｈ７的编码ｅａｅ蛋白的ｅａｅＡ基因和大肠杆菌编码Ｈ７抗原的ｆｌｉＣ基因的核甘酸序列,合成了２对寡核苷酸引物,建立了一个检测大肠杆菌Ｏ１５７∶Ｈ７的ＰＣＲ方法。对１１株已知大肠杆菌Ｏ１５７∶Ｈ７（ＮＭ;无运动性）株和其他不同属的４２株已知肠道致病菌的检测结果表明,该方法只从大肠杆菌Ｏ１５７∶Ｈ７（ＮＭ）株的ＤＮＡ中产生预期的扩增产物,而从其他菌株的ＤＮＡ中未扩增出任何ＤＮＡ产物。该方法从基因水平直接确定大肠杆菌的血清型,特异性强,克服了以往血清学方法有非特异性反应的缺陷,为检测和鉴定大肠杆菌Ｏ１５７∶Ｈ７（ＮＭ）提供了一个新方法。     

Influence of age,sex and herd characteristics on the occurrence of Verocytotoxin-producing Escherichia coli O157 in Danish dairy farms

Verocytotoxin-producing Escherichia coli (VTEC) O157 is an important emerging human pathogen. Cattle are considered to be the main reservoir for VTEC O157. The objectives of this study were to determine the prevalence of VTEC O157 in Danish dairy herds and to investigate the relationship between shedding of VTEC O157 and a number of animal and herd characteristics. Sixty dairy farms were visited once in August-October, and from each herd faecal samples from up to 50 animals were analysed for VTEC O157 by enrichment, immunomagnetic separation (IMS), and plating on selective agar. In total, 2419 animals were sampled, and 3.6% of these excreted VTEC O157. These animals were located on 10 farms (17%). On average, 21% of the sampled animals in the positive herds excreted VTEC O157. Register data, including age, sex, breed, housing conditions and herd composition, were extracted from a database. No influence of herd size or housing conditions was found. A strong effect of age was seen with 2-6-month-old calves as the high-risk age group (8.6% positive) in contrast to calves <2 months (0.7%) and cows (2.4%). There was a non-significant tendency of bull calves to have a higher prevalence than heifers within the age group of 2-6 months. Significantly, more of the herds characterised by having relatively many bull calves or many animals bought into the herd were positive for VTEC O157. Despite the low incidence of human VTEC O157 infections in Denmark, the prevalence in Danish dairy herds was found to be at a similar level as in many other countries.     

Escherichia coli O157:H7 in healthy dairy cows

Faecal samples were taken from 371 cows originating from 55 dairy farms and slaughtered at one slaughterhouse; tonsils were taken from 215 of these animals. Escherichia coli 0157:H7 was found in the faeces of only two animals and was not found in any tonsils. The farm supplying the first positive cow detected at the slaughterhouse was visited 3 months later and 160 animals (80 cows and 80 heifers) were tested by rectal swabs; E. coli 0157:H7 was not isolated.     

Significance of Escherichia coli O157 in sheep at slaughter in Switzerland

The importance of latent zoonoses has increased in recent years in view of foodborne diseases: (i) the "healthy" animal repesents a reservoir for specific pathogens; () no pathological-anatomical changes in the carcass and its organs show the presence of these pathogens; and (iii) these pathogens may enter the food chain via hygienic weak points in the slaughtering process. To estimate the risks involved and to take appropriate measures, analysis of the slaughtering process should be complemented by collecting data relating to the carriage of the animals of latent zoonotic pathogens. From October 2004 to June 2005, fecal samples from 630 slaughtered sheep were enriched and then examied by IMS technique and by PCR to assess the prevalence of E. coli O157 (OE). Seven samples (1.1%), distributed throughout the whole examination period, were found to be positive. To assess the potential pathogenicity for humans, E. coli O157 strains were isolated by colony hybridization and further characterized. The isolated strains fermented Sorbitol, showed four different H tys (H7, H12, H38, H48), and were all negative for stx. One O157:H7 strain harbored the gene for intimin (eae) in combination with ehxA, and paa. In consequence, the potential health hazard from sheep meat related to O157 STEC seems current not to be of particular importance in Switzerland. Results emphasize the fact that E. coli O157 are not always STEC but may belong to other pathotypes as nontraditional EPEC.     

Environmental sources and transmission of Escherichia coli O157 in feedlot cattle

A study was conducted in 2 feedlots in southern Alberta to identify environmental sources and management factors associated with the prevalence and transmission of Escherichia coli O157:H7. Escherichia coli O157:H7 was isolated in preslaughter pens of cattle from feces (0.8%), feedbunks (1.7%), water troughs (12%), and incoming water supplies (4.5%), but not from fresh total mixed rations. Fresh total mixed rations did not support the growth of E. coli O157:H7 and E. coli from bovine feces following experimental inoculation. Within a feedlot, the feces, water troughs, and feedbunks shared a few indistinguishable subtypes of E. coli O157:H7. A few subtypes were repeatedly isolated in the same feedlot, and the 2 feedlots shared a few indistinguishable subtypes. The prevalence of E. coli O157:H7 in water troughs of preslaughter cattle in 1 feedlot was associated with season, maximum climatic temperatures the week before sampling; total precipitation the week before sampling, and coliform and E. coli counts in the water trough.