Isolation of Escherichia coli O157:H7 from dung beetles Catharsius molossus

In an epidemiological survey, Escherichia coli O157:H7 was isolated from the intestine 4 of 113 dung beetle Catharsius molossus captured below ground at Tongshan County, Jiangsu Province of China. In parallel, 10 strains of E. coli O157:H7 were isolated from fecal samples of 383 diarrhea patients from the same region. Most importantly, using pulsed field gel electrophoresis (PFGE) of chromosomal DNA restriction fragments and PCR method, we found that the PFGE pattern and virulence genes of beetle isolates were identical to those of the human isolates, such as Shiga-toxins (stx) and enterohemorrhagic Escherichia coli hemolysin A (EHEC-hlyA). Therefore, dung beetle might acquire pathogenic E. coli O157:H7 through contact with feces of domestic animals.     

Occurrence of Escherichia coli O157:H7 in faeces, skin and carcasses from sheep and goats in Ethiopia

Aims:  To determine the occurrence and proportion of Escherichia coli O157:H7 in faeces, skin swabs and carcasses before and after washing, from sheep and goats in Ethiopia.
Method and Results:  Individual samples were enriched in modified tryptic soy broth with novobiocin, concentrated using immunomagnetic separation (IMS) and plated onto cefixime-tellurite containing sorbitol MacConkey agar. Presumptive colonies were confirmed by biochemical tests and subjected to latex agglutination tests. A PCR was performed on isolates for the detection of stx ₁, stx ₂ and eae genes. Escherichia coli O157:H7 was isolated from faeces (4·7%), skin swabs (8·7%) and carcasses before washing (8·1%) and after washing (8·7%) and on water samples (4·2%). The proportion of carcasses contaminated with E. coli O157:H7 was strongly associated with those recovered from faecal and skin samples. Both stx ₁ and stx ₂ genes were identified from one E. coli O157:H7 isolate from a goat carcass.
Conclusions:  Even though the numbers of samples examined in this study were limited to one abattoir, sheep and goats can be potential sources of E. coli O157:H7 for human infection in the country. Control measures to reduce the public health risks arising from E.   coli O157:H7 in reservoir animals need to be addressed at abattoir levels by reducing skin and faecal sources and carcass contaminations at different stages of slaughter operations.
Significance and Impact of the Study:  Escherichia coli O157:H7 was detected from carcasses before and after washing during slaughtering operations, and one O157 isolate was positive for verotoxins.     

Prevalence and characterization of shiga toxin-producing Escherichia coli in swine feces recovered in the National Animal Health Monitoring System's Swine 2000 study

A study was conducted to determine the prevalence of Shiga toxin-producing Escherichia coli (STEC) in swine feces in the United States as part of the National Animal Health Monitoring System's Swine 2000 study. Fecal samples collected from swine operations from 13 of the top 17 swine-producing states were tested for the presence of STEC. After enrichment of swine fecal samples in tryptic soy broth, the samples were tested for the presence of stx1 and stx2 by use of the TaqMan E. coli STX1 and STX2 PCR assays. Enrichments of samples positive for stx1 and/or stx2 were plated, and colony hybridization was performed using digoxigenin-labeled probes complementary to the stx1 and stx2 genes. Positive colonies were picked and confirmed by PCR for the presence of the stx1, stx2, or stx2e genes, and the isolates were serotyped. Out of 687 fecal samples tested using the TaqMan assays, 70% (484 of 687) were positive for Shiga toxin genes, and 54% (370 of 687), 64% (436 of 687), and 38% (261 of 687) were positive for stx1, stx2, and both toxin genes, respectively. Out of 219 isolates that were characterized, 29 (13%) produced stx1, 14 (6%) produced stx2, and 176 (80%) produced stx2e. Twenty-three fecal samples contained at least two STEC strains that had different serotypes but that had the same toxin genes or included a strain that possessed stx1 in addition to a strain that possessed stx2 or stx2e. The STEC isolates belonged to various serogroups, including O2, O5, O7, O8, O9, OX10, O11, O15, OX18, O20, O57, O65, O68, O69, O78, O91, O96, O100, O101, O120, O121, O152, O159, O160, O163, and O untypeable. It is noteworthy that no isolates of serogroup O157 were recovered. Results of this study indicate that swine in the United States harbor STEC that can potentially cause human illness.     

Development of a multiplex PCR approach for the identification of Shiga toxin-producing Escherichia coli strains and their major virulence factor genes

AIMS: To develop and evaluate a multiplex PCR (mPCR) system for rapid and specific identification of Shiga toxin-producing Escherichia coli (STEC) and their main virulence marker genes. METHODS AND RESULTS: A series of mPCR assays were developed using primer pairs that identify the sequences of Shiga toxins 1 and 2 (stx1 and stx2, including the stx2c, stx2d, stx2e and stx2f variants), intimin (eaeA), and enterohaemorrhagic E. coli enterohaemolysin (ehlyA). Moreover, two additional genes (rfb O157 and fliC H7), providing the genotypic identification of the O157:H7 E. coli serotype, were detected. As an internal positive control, primers designated to amplify the E. coli 16S rRNA were included in each mPCR. All the amplified genes in the E. coli reference strains were sucessfully identified by this procedure. The method was then used for the examination of 202 E. coli isolates recovered from cattle and children. Among them, 25 (12.4%) were stx positive including the strains of O157:H7 serotype (six isolates) and O157:NM serogroup (four strains). Moreover, 20 STEC strains possessed the eaeA (intimin) and ehlyA (enterohaemolysin) genes. CONCLUSIONS: The developed mPCR-based system enabled specific detection of STEC bacteria and identification of their main virulence marker genes. SIGNIFICANCE AND IMPACT OF THE STUDY: The ability to identify STEC bacteria and the majority of their virulence gene markers, including four variants of Shiga toxin, as well as the differentiation of O157:H7 from non-O157 isolates represents a considerable advancement over other PCR-based methods for rapid characterization of STEC.     

Isolation of Escherichia coli O157:H7 strains that do not produce Shiga toxin from bovine, avian and environmental sources

AIMS: To determine the potential for naturally occurring Shiga toxin-negative Escherichia coli O157 to acquire stx(2) genes. METHODS AND RESULTS: Multiple E. coli O157:H7 isolates positive for eae and ehxA, but not for stx genes, were isolated from cattle, water trough sediment, animal bedding and wild bird sources on several Ohio dairy farms. These isolates were experimentally lysogenized by stx(2)-converting bacteriophage. CONCLUSIONS: Shiga toxin-negative strains of E. coli O157 are present in multiple animal and environmental sources. SIGNIFICANCE AND IMPACT OF THE STUDY: Shiga toxin-negative strains of E. coli O157 present in the food production environment are able to acquire the stx genes, demonstrating their potential to emerge as new Shiga toxin-producing E. coli strains.     

Fate of Escherichia coli O157:H7 and Salmonella from contaminated manure slurry applied to soil surrounding tall fescue

Aim:  To investigate the potential transfer of Escherichia coli O157:H7 and Salmonella from contaminated manure slurry into the tissue of tall fescue plants.
Methods and Results:  Tall fescue plants ( n  =   50) were fertilized with a manure slurry inoculated with E. coli O157:H7 and Salmonella . Soil was collected and tall fescue plants ( n  =   10 per day) harvested on day 1, 2, 4, 8, and 14 after manure slurry fertilization. Soil samples were positive for E. coli O157:H7 on all days and on day 1, 2, 8, and 14 for Salmonella . None of the plant tissue samples were positive for E. coli O157:H7 on day 1 or 2; however, 20%, 30% and 40% of plant tissue samples were positive for E. coli O157:H7 on day 4, 8, and 14, respectively.
Conclusions:  It may be possible that E. coli O157:H7 can become transmitted and internalized into tall fescue plant tissue within 4 days after exposure to an E. coli O157:H7-contaminated manure slurry. Salmonella did not appear to be transferred to tall fescue plant tissue.
Significance and Impact of the Study:  Faeces contaminated with E. coli O157:11H7 may be one means by which grazing ruminants spread bacterial pathogens to additional animals.     

Genetic characteristics and antimicrobial resistance of Escherichia coli from Japanese macaques (Macaca fuscata) in rural Japan

Escherichia coli was isolated from wild and captive Japanese macaques (Macaca fuscata) to investigate the risk of zoonotic infections and the prevalence of antimicrobial-resistant Escherichia coli in the wild macaque population in Shimokita Peninsula, a rural area of Japan. We collected 265 fresh fecal samples from wild macaques and 20 samples from captive macaques in 2005 and 2006 for E. coli isolation. The predominant isolates were characterized by serotyping, virulence gene profiling, plasmid profiling, pulsed-field gel electrophoresis (PFGE), and microbial sensitivity tests. In total, 248 E. coli strains were isolated from 159 fecal samples from wild macaques, and 42 E. coli were isolated from 17 samples from captive macaques. None of the virulence genes eae, stx, elt, and est were detected in any of the isolates. The relatedness between wild- and captive-derived isolates was low by serotyping, PFGE, and plasmid profiling. Serotypes O8:H6, O8:H34, O8:H42, O8:HUT, O103:H27, O103:HNM, and OUT:H27 were found in wild macaque feces; serotypes O157:H42 and O119:H21 were recovered from captive macaques. O-and H-serotypes of the 26 isolates were not typed by commercial typing antisera and were named OUT and HUT, respectively. Twenty-eight isolates had no flagellar antigen, and their H-serotypes were named HNM. Similarity of PFGE patterns between wild-derived isolates and captive-derived isolates was <70%. No plasmid profile was shared between wild-derived and captive-derived isolates. The prevalence of antimicrobial-resistant E. coli was 6.5% (n=62) in wild macaques, and these isolates were resistant to cephalothin. We conclude that wild Japanese macaques in Shimokita Peninsula were unlikely to act as a reservoir of pathogenic E. coli for humans and that antimicrobial-resistant E. coli in wild macaques may be derived from humans.     

Prevalence and characteristics of shiga toxin-producing Escherichia coli from healthy cattle in Japan

The prevalence of Shiga toxin-producing Escherichia coli (STEC) in Japan was examined by using stool samples from 87 calves, 88 heifers, and 183 cows on 78 farms. As determined by screening with stx-PCR, the prevalence was 46% in calves, 66% in heifers, and 69% in cows; as determined by nested stx-PCR, the prevalence was 100% in all animal groups. Of the 962 isolates picked by colony stx hybridization, 92 isolates from 54 farms were characterized to determine their O serogroups, virulence factor genes, and antimicrobial resistance. Of these 92 isolates, 74 (80%) could be classified into O serogroups; 50% of these 74 isolates belonged to O serogroups O8, O26, O84, O113, and O116 and 1 isolate belonged to O serogroup O157. Locus of enterocyte effacement genes were detected in 24% of the isolates, and enterohemorrhagic E. coli (EHEC) hlyA genes were detected in 72% of the isolates. Neither the bundle-forming pilus gene nor the enteropathogenic E. coli adherence factor plasmid was found. STEC strains with characteristics typical of isolates from human EHEC infections, which were regarded as potential EHEC strains, were present on 11.5% of the farms.     

Prevalence and characterization of non-O157 Shiga toxin-producing Escherichia coli on carcasses in commercial beef cattle processing plants

Beef carcass sponge samples collected from July to August 1999 at four large processing plants in the United States were surveyed for the presence of non-O157 Shiga toxin-producing Escherichia coli (STEC). Twenty-eight (93%) of 30 single-source lots surveyed included at least one sample containing non-O157 STEC. Of 334 carcasses sampled prior to evisceration, 180 (54%) were found to harbor non-O157 STEC. Non-O157 STEC isolates were also recovered from 27 (8%) of 326 carcasses sampled after the application of antimicrobial interventions. Altogether, 361 non-O157 STEC isolates, comprising 41 different O serogroups, were recovered. O serogroups that previously have been associated with human disease accounted for 178 (49%) of 361 isolates. Although 40 isolates (11%) carried a combination of virulence factor genes (enterohemorrhagic E. coli hlyA, eae, and at least one stx gene) frequently associated with STEC strains causing severe human disease, only 12 of these isolates also belonged to an O serogroup previously associated with human disease. Combining previously reported data on O157-positive samples (R. O. Elder, J. E. Keen, G. R. Siragusa, G. A. Barkocy-Gallagher, M. Koohmaraie, and W. W. Laegreid, Proc. Natl. Acad. Sci. USA 97:2999-3003, 2000) with these data regarding non-O157-positive samples indicated total STEC prevalences of 72 and 10% in preevisceration and postprocessing beef carcass samples, respectively, showing that the interventions used by the beef-processing industry effected a sevenfold reduction in carcass contamination by STEC.     

Impact of microbial diversity on rapid detection of enterohemorrhagic Escherichia coli in surface waters

Enterohemorrhagic Escherichia coli (EHEC) are a physiologically, immunologically and genetically diverse collection of strains that pose a serious water-borne threat to human health. Consequently, immunological and PCR assays have been developed for the rapid, sensitive detection of presumptive EHEC. However, the ability of these assays to consistently detect presumptive EHEC while excluding closely related non-EHEC strains has not been documented. We conducted a 30-month monitoring study of a major metropolitan watershed. Surface water samples were analyzed using an immunological assay for E. coli O157 (the predominant strain worldwide) and a multiplex PCR assay for the virulence genes stx(1), stx(2) and eae. The mean frequency of water samples positive for the presence of E. coli O157, stx(1) or stx(2) genes, or the eae gene was 50%, 26% and 96%, respectively. Quantitative analysis of selected enriched water samples indicated that even in samples positive for E. coli O157 cells, stx(1)/stx(2) genes, and the eae gene, the concentrations were rarely comparable. Seventeen E. coli O157 strains were isolated, however, none were EHEC. These data indicate the presence of multiple strains similar to EHEC but less pathogenic. These findings have important ramifications for the rapid detection of presumptive EHEC; namely, that current immunological or PCR assays cannot reliably identify water-borne EHEC strains.     

产志贺毒素大肠埃希菌的分子生物学鉴定和耐药性分析

为了解产志贺毒素大肠埃希菌 (Shigatoxin producingEscherichiacoli ,STEC)stx1,stx2 ,eaeA ,hlyA 4种毒力基因的分布情况 ,以及分离株对 18种抗生素的敏感性 ,采用多重PCR(multiplexPCR ,mPCR)法对分离株进行毒力基因的分子生物学鉴定 ;用WHO推荐的K B法对分离株进行抗生素的敏感性测定。产志贺毒素的大肠埃希菌共有 4 6株 ,其中 2种毒素均产生的有 2 2株 (4 7.8% ) ;单纯产生stx1的有 16株 (36 .9% ) ,stx2 的有 8株 (17.4 % ) ;4种毒力基因均存在的有 19株 (4 1.3% ) ,血清型为O15 7∶H7,而非O15 7∶H7血清型的菌株 (2 3/46 )中 ,4种毒力基因同时存在的仅有 3株 (6 .6 % ) ,但有 13株 (5 6 .9% )hlyA基因阳性。全部STEC对复方新诺明耐药 ,对链霉素耐药率为 2 8.3% ,氨苄西林为 30 .4 % ,红霉素为 6 9.6 % ,而且有 5株对至少 4种以上抗生素多重耐药 ,耐药谱为复方新诺明 链霉素 红霉素 氨苄西林。非O15 7型STEC耐药菌次为 12 2 ,而O15 7型为 6 3。可见 ,mPCR法可以快速检测STEC特征性毒力基因 ,以判定其致病性能。非O15 7型STEC对抗生素较易形成耐药性。     

Association of Escherichia coli O157:H7 with houseflies on a cattle farm

The ecology of Escherichia coli O157:H7 is not well understood. The aims of this study were to determine the prevalence of and characterize E. coli O157:H7 associated with houseflies (HF). Musca domestica L. HF (n = 3,440) were collected from two sites on a cattle farm over a 4-month period and processed individually for E. coli O157:H7 isolation and quantification. The prevalence of E. coli O157:H7 was 2.9 and 1.4% in HF collected from feed bunks and a cattle feed storage shed, respectively. E. coli O157:H7 counts ranged from 3.0 x 10(1) to 1.5 x 10(5) CFU among the positive HF. PCR analysis of the E. coli O157:H7 isolates revealed that 90.4, 99.2, 99.2, and 100% of them (n = 125) possessed the stx1, stx2, eaeA, and fliC genes, respectively. Large populations of HF on cattle farms may play a role in the dissemination of E. coli O157:H7 among animals and to the surrounding environment.     

Isolation of potentially pathogenic Escherichia coli O157:H7 from the Ganges River

Escherichia coli serotype O157:H7 was detected among bacteria collected from the Ganges River. O157:H7 isolates tested positive for stx(1), stx(2), and eae gene sequences. Identification of potentially pathogenic isolates from extensively used source water indicates that O157:H7 may be a significant but as yet underacknowledged public health concern in India.     

Phylogenetically related Argentinean and Australian Escherichia coli O157 isolates are distinguished by virulence clades and alternative Shiga toxin 1 and 2 prophages

Shiga toxigenic Escherichia coli O157 is the leading cause of hemolytic uremic syndrome (HUS) worldwide. The frequencies of stx genotypes and the incidences of O157-related illness and HUS vary significantly between Argentina and Australia. Locus-specific polymorphism analysis revealed that lineage I/II (LI/II) E. coli O157 isolates were most prevalent in Argentina (90%) and Australia (88%). Argentinean LI/II isolates were shown to belong to clades 4 (28%) and 8 (72%), while Australian LI/II isolates were identified as clades 6 (15%), 7 (83%), and 8 (2%). Clade 8 was significantly associated with Shiga toxin bacteriophage insertion (SBI) type stx(2) (locus of insertion, argW) in Argentinean isolates (P < 0.0001). In Argentinean LI/II strains, stx(2) is carried by a prophage inserted at argW, whereas in Australian LI/II strains the argW locus is occupied by the novel stx(1) prophage. In both Argentinean and Australian LI/II strains, stx(2c) is almost exclusively carried by a prophage inserted at sbcB. However, alternative q(933)- or q(21)-related alleles were identified in the Australian stx(2c) prophage. Argentinean LI/II isolates were also distinguished from Australian isolates by the presence of the putative virulence determinant ECSP_3286 and the predominance of motile O157:H7 strains. Characteristics common to both Argentinean and Australian LI/II O157 strains included the presence of putative virulence determinants (ECSP_3620, ECSP_0242, ECSP_2687, ECSP_2870, and ECSP_2872) and the predominance of the tir255T allele. These data support further understanding of O157 phylogeny and may foster greater insight into the differential virulence of O157 lineages.     

Fluctuations in the occurrence of Escherichia coli O157:H7 on a Norwegian farm*

AIM: To describe the distribution of Escherichia coli O157:H7 on a sporadically positive dairy farm and on possible contact farms over a one-year period. METHODS AND RESULTS: Environmental and faecal samples from all animals at the farm, and faecal samples from animals at contact farms were analysed for E. coli O157:H7 by immunomagnetic separation methods or VIDAS.Confirmed isolates were tested for cytotoxicity in the Vero cell assay and typed by PFGE. Escherichia coli O157:H7 (stx2 and eae) of the same PFGE type were isolated from cattle, sheep, hens and environmental samples at variable levels during summer and fall 2002, but were not detected in 2003. CONCLUSIONS: Escherichia coli O157:H7 had a widespread distribution on the farm investigated, but the original source of contamination could not be identified. The occurrence of this bacterium on the farm did not result in any detectable increase in gastrointestinal disease in the associated population. SIGNIFICANCE AND IMPACT OF THE STUDY: Despite a low endemic level of E. coli O157:H7 in the Norwegian cattle population, the growth and spread of this potentially important bacterium may occur.     

Prevalence of Escherichia coli strains in the canteens

The prevalence of enteropathogenic (EPEC) and enterohaemorrhagic (EHEC) E. coli strains in stool specimens from asymptomatic human carriers working in the canteens and also in the kitchen and sanitary facilities was evaluated. The E. coli genes coding for the following virulence markers: intimin (eae), enterohaemolysin (hlyA), and verotoxins type I and II (stx1 and stx2) were sought by multiplex PCR assay. E. coli isolates were obtained from 144 stool specimens, 295 swabs taken from kitchen hardware and surrounding facilities, and from 33 meat specimens. Only 66 (8.5%) of total 777 E. coli isolates belonged to O44, O18, O25, O127, O55, O114, O125, and O142 serogroups, the prevalent serogroups in Poland. None of the strains was classified as serogroup O157. The serogroups O44 and O18 were present most often among all typeable strains and their incidence was 51.5% and 25.8% respectively. Among 363 isolates assayed for the presence of the genes encoding virulence markers only 10 isolates (2.8%) carried eae gene. None of the isolates possessing eae gene belonged to the serogroups tested. The hlyA, stx1 and stx2 genes were absent in all E. coli isolates tested.     

Influence of indigenous eukaryotic microbial communities on the reduction of Escherichia coli O157:H7 in compost slurry

Compost made from livestock manure is commonly used as a crop fertilizer and serves as a possible vehicle for the transmission of Escherichia coli O157:H7 to fresh produce. In this study, we hypothesized that the indigenous microbial communities present in composts adversely affects the survival of E. coli O157:H7. Escherichia coli O157:H7 was spiked into compost slurry and incubated at 25 °C. Escherichia coli O157:H7 exhibited a c. 4 log(10) reduction over 16 days. When compost was supplemented with the eukaryotic inhibitor cycloheximide, there was a minimal decrease in E. coli O157:H7 counts over the same time period. Analysis of microbial communities present in the compost with denaturing gradient gel electrophoresis (DGGE) suggested minor differences in the fungal communities present in cycloheximide-treated compost, compared with untreated compost over a period of 12 days at 25 °C. However, the DGGE profiles of protists showed drastic differences in community complexity. Clone library sequence analysis of protist populations revealed significantly different species composition between treatment and control samples at different time points. This suggests that predation of E. coli O157:H7 by protists might be a potential mechanism for reducing E. coli O157:H7 in compost materials.     

Shiga-toxin-producing Escherichia coli in faeces of healthy dairy cows, sheep and goats: prevalence and virulence properties

The prevalence of Shiga-toxin-producing Escherichia coli (STEC) in healthy dairy ruminants was investigated between 1996 and 1998 by a multiplex polymerase chain reaction (mPCR) technique. A total of 13 552 E. coli colonies from 726 cows, 28 sheep and 93 goats out of 112 randomly selected dairy farms in Hessia, Germany were analysed. STEC strains were recovered from 131 (18.0%) cows, nine (32.1%) sheep and 70 (75.3%) goats. Further characterization of the STEC isolates showed that 89 (0.66% of the investigated colonies) of animal field strains carried stx1 gene, 64 (0.47%) stx2 gene and 57 (0.42%) stx1 and stx2 gene. Sixty (93.8%) out of 64 stx2 field strains were harboured by cows. In contrast, 74 (83.1%) out of 89 stx1 dairy animal field strains were from ovine or caprine origin. Only 17 (8. 1%) stx-positive isolates (13 from cattle, three from sheep and only one from goat) were positive for eaeA gene. Eight (9.0%) of the stx1, five (7.8%) of the stx2 and four (7.0%) of the stx1/stx2 gene-positive field strains carried the eaeA gene. The prevalence of EHEC-haemolysin (EHEC-hlyA) gene sequence was 88.8% (79 isolates) of the stx1 and 68.8% (44 isolates) of the stx2 isolates. Out of 57 stx1- and stx2-positive field-strains, 34 (59.6%) carried the EHEC-hlyA gene. E. coli O serovars O:157 and O:111 were not found. Only one isolate was positive with O26 antiserum.     

Fate of Escherichia coli O157 and detection of stx phage during fermentation of maize, an animal feedstuff

AIMS: The fate of inoculated Escherichia coli O157, stx phages and the physico-chemical properties of maize were studied during laboratory-scale fermentation by naturally occurring lactic acid bacteria. METHODS AND RESULTS: Before fermentation, chopped maize was inoculated with 6.2 log(10) CFU g(-1) of a five-isolate mixture of E. coli O157. After fermentation, the silage contained 70.6 g kg(-1) dry matter (DM) lactic acid and 12.8 g kg(-1) DM acetic acid and was pH 4.0. Levels of E. coli O157 fell rapidly, and none of the five isolates could be recovered from the fermenting maize after 8 days. Using a resuscitation step did not consistently enhance recovery of E. coli O157. Stx phages were not isolated from the fermenting maize at any time. Pulsed-field gel electrophoresis (PFGE) genotyping showed that E. coli O157 2975 and 64a/01 survived better than the other three isolates studied. Escherichia coli O157 isolate 1474/00 was particularly sensitive to the laboratory procedures used to harvest the inocula and contaminate the maize. Some colonies recovered during the fermentation had one to three band alterations compared with the initial PFGE genotypes. SIGNIFICANCE AND IMPACT OF THE STUDY: None of the five different E. coli O157 genotypes survived maize fermentation. Fermentation of maize produces an animal feedstuff that is unlikely to contain E. coli O157 or stx phages.     

Prevalence and characterization of non-O157 shiga toxin-producing Escherichia coli isolates from commercial ground beef in the United States

Escherichia coli O157:H7 is a Shiga toxin (stx)-producing E. coli (STEC) strain that has been classified as an adulterant in U.S. beef. However, numerous other non-O157 STEC strains are associated with diseases of various severities and have become an increasing concern to the beef industry, regulatory officials, and the public. This study reports on the prevalence and characterization of non-O157 STEC in commercial ground beef samples (n = 4,133) obtained from numerous manufacturers across the United States over a period of 24 months. All samples were screened by DNA amplification for the presence of Shiga toxin genes, which were present in 1,006 (24.3%) of the samples. Then, culture isolation of an STEC isolate from all samples that contained stx(1) and/or stx(2) was attempted. Of the 1,006 positive ground beef samples screened for stx, 300 (7.3% of the total of 4,133) were confirmed to have at least one strain of STEC present by culture isolation. In total, 338 unique STEC isolates were recovered from the 300 samples that yielded an STEC isolate. All unique STEC isolates were serotyped and were characterized for the presence of known virulence factors. These included Shiga toxin subtypes, intimin subtypes, and accessory virulence factors related to adherence (saa, iha, lifA), toxicity (cnf, subA, astA), iron acquisition (chuA), and the presence of the large 60-MDa virulence plasmid (espP, etpD, toxB, katP, toxB). The isolates were also characterized by use of a pathogenicity molecular risk assessment (MRA; based on the presence of various O-island nle genes). Results of this characterization identified 10 STEC isolates (0.24% of the 4,133 total) that may be considered a significant food safety threat, defined by the presence of eae, subA, and nle genes.