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1.
The presence of 12 genes associated with virulence in human attaching and effacing Escherichia coli (AEEC) was studied within a collection of 20 enterohemorrhagic E. coli (EHEC) and 206 atypical enteropathogenic E. coli (EPEC) isolated from ruminants. In addition, virulence genes and the clonal relationship of 49 atypical EPEC O26 strains isolated from humans and ruminants were compared to clarify whether ruminants serve as a reservoir of atypical EPEC for humans. A great diversity in the content of virulence gene was found. Thus, the espH, espG and map genes were detected in more than 85% of ruminant AEEC strains; the tccP2, espI, efa1/lifA, ehxA and paa genes were present in 50-70% of strains; and other genes such as tccP, espP, katP and toxB were detected in <25% of strains. EHEC strains contained more virulence genes than atypical EPEC strains. Our results suggest for the first time that the efa1/lifA gene is associated with diarrhea in newborn ruminants and that the AEEC strains with the H11 flagellar antigen are potentially more virulent than the non-H11 AEEC strains. Importantly, we identified a new intimin variant gene, eaeρ, in three ruminant atypical EPEC strains. The comparison of ruminant and human EPEC O26 strains showed that some ruminant strains possess virulence gene profiles and pulse-field gel electrophoresis pulsotypes similar to those of human strains. In conclusion, our data suggest that atypical EPEC is a heterogeneous group with different pathogenic potential and that ruminants could serve as a reservoir of atypical EPEC for humans.  相似文献   

2.
《Veterinary microbiology》1997,54(2):145-153
Nineteen Escherichia coli strains belonging to enteropathogenic (EPEC) serogroups were isolated from calves with diarrhea in Paraná State, Brazil, and studied for virulence markers associated with EPEC or enterohemorrhagic E. coli (EHEC). The 19 isolates belonged to 12 serotypes with isolates of O26:H11, O119:H25 and O114:H− being the most prevalent. Localized adherence (LA) was demonstrated for 37% of the isolates, consisting of all four O26:H11, both O114:H− and one O114:H40 isolates. All the LA strains were positive in the fluorescent-actin staining (FAS) test and possessed attaching-effacing E. coli (eae) sequences, but only O114 strains hybridized with the EPEC adherence factor (EAF) probe. None of the strains produced Shiga-like toxins (Verotoxin). Only the O26:H11 strains hybridized with the EHEC plasmid specific (CVD419) probe and were enterohemolytic, properties associated with EHEC strains. This investigation demonstrates that among the bovine strains isolated only those of serogroup O114 behaved as typical EPEC.  相似文献   

3.
Domestic animals belonging to seven different species (cattle, sheep, dogs, cats, pigs, chicken and goats) were investigated as natural reservoirs for attaching and effacing Escherichia coli (AEEC). For this, 2165 E. coli strains from faeces of 803 animals were examined for the presence of the intimin -(eae) gene as a characteristic of AEEC strains. Ten percent of the animals were found to excrete AEEC, most frequently found in sheep (19.2%) and pigs (17.6), followed by cattle (10.4%), dogs (7.2%), cats (6.5%) and poultry (2.3%). The 97 AEEC strains from animals were grouped into 44 serotypes. Only four E. coli serotypes (O2:H8, O26:[H11], O109:[H25] and O145:[H28] were found in more than one animal host species. AEEC O26:[H11] strains were most frequently isolated (13.4%) being present in cattle, poultry, pigs and sheep. A search for virulence markers associated with enterohemorrhagic E. coli (EHEC) revealed Shiga-toxin genes in three (3.1%) AEEC strains from sheep. Bundle forming pili genes as a trait of typical enteropathogenic E. coli (EPEC) were detected in four (4.1%) strains from dogs and cats. The remaining 90 AEEC strains were classified as atypical EPEC. Typing of intimin genes revealed intimin beta being present in 51.5% of the strains, followed by intimins theta (23.7%), epsilon (6.2%), kappa (5.2%), zeta (5.2%), alpha, eta and iota (each 1.0%). Our data indicate that domestic animals and pets constitute an important natural reservoir of AEEC strains, and some of these (O26:[H11], O103:H2, O128:H2, O145:[H28] and O177:[H11]) are known to occur as pathogens in humans.  相似文献   

4.
The aims of this study were to investigate the prevalence, antibiotic resistance, presence of class 1 and 2 integrons, Extended Spectrum β-Lactamases (ESBL) genes, phylogenetic group and epidemiological relationships of EPEC, ETEC and EHEC pathotypes isolated from patients with diarrhea and farm animals in south east region of Iran. A total of 671 diarrheagenic E. coli (DEC) were collected from stool samples of 395 patients with diarrhea and 276 farm cattles and goats. Presence of EPEC, ETEC and EHEC were identified using multiplex-PCR employing primers targeted the shiga toxin (stx), intimin (eae), bundle forming pili (bfp), and enterotoxins (lt and st) genes. The highest proportion of the patients (64%) were children under age 1–15 year (p ≤ 0.05). Among the isolates, atypical EPEC was detected in 26 patients and 14 animal stool samples, while typical EPEC was found in 2 cattles. ETEC isolates were detected in stools of 13 patients and 4 EHEC was identified in 3 goats and one cattle. The isolates were checked for susceptibility to 14 antibiotics. 50% (n = 13) of EPEC and 61.5% (n =8) of ETEC showed multi-drug resistance (MDR) profiles and one EPEC was found to be extensive drug resistant (XDR). In contrast, EHEC isolates were susceptible to the majority of antimicrobial agents. The MDR isolates were positive for blaTEM and blaCTX-M ESBL genes and carried class 1 integrons. Further study on the biofilm formation indicated that, 3 out of 4 EHEC isolates showed strong biofilm, while other pathotypes had either moderate, weak or no biofilm activity. Majority of EPEC isolates were belonged to phylogenetic group B1, all except one ETEC were classified as phylogenetic group A and two EHEC were belonged to phylogroup D, respectively. A multilocus variable tandem repeat analysis (MLVA) exhibited 22 distinct patterns. In conclusion, MLVA data showed high clonal diversity. Presence of EHEC in animal origins pose public health concern in this region.  相似文献   

5.
Antimicrobial resistance profile of E. coli and Salmonella serovars isolated from diarrheic calves and handlers in Egypt is unknown due to the absence of monitoring. Therefore, this study aimed to determine the virulence, genetic and antimicrobial resistance profiles of E. coli and Salmonella serovars associated with diarrhea in calves and handlers in intensive dairy farms in Egypt. A total of 36 bacterial strains (20 E. coli and 16 Salmonella) were isolated from fecal samples of 80 diarrheic Holstein dairy calves (10 E. coli and 13 Salmonella) and hand swabs of 35 handlers (10 E. coli and 3 Salmonella) in two intensive dairy farms in Sharkia Governate in Egypt. E. coli strains belonged to six different serogroups and O114:K90 was the most prevalent serogroup (30%). However, Salmonella strains were serotyped into four different serogroups and S. Kiel was the most prevalent serotype (50%). Thirteen (65%) E. coli isolates were harbouring either stx2, eaeA and/or astA virulence-associated genes. However, stn and spvC virulence genes were detected in 2 (12.5%) and 4 (25%) of Salmonella isolates, respectively. E. coli isolates showed marked resistance to ampicillin (75%), while Salmonella strains exhibited high resistance to amikacin (100%), gentamicin (93.75%) and tobramycin (87.5%). Results of the present study showed that E. coli and Salmonella serovars isolated from diarrheic calves and handlers in intensive dairy farms in Egypt exhibited resistance to multiple classes of antimicrobials, which may pose a public health hazard. Thus, the continuous monitoring of antimicrobial resistance is necessary for both humans and veterinary medicine to decrease the economic losses caused by antimicrobial-resistant strains in animals as well as the zoonotic risk.  相似文献   

6.
Initial adherence to host cells is the first step of the infection of enteropathogenic Escherichia coli (EPEC), enterohaemorrhagic Escherichia coli (EHEC) and verotoxigenic Escherichia coli (VTEC) strains. The importance of this step in the infection resides in the fact that (1) adherence is the first contact between bacteria and intestinal cells without which the other steps cannot occur and (2) adherence is the basis of host specificity for a lot of pathogens. This review describes the initial adhesins of the EPEC, EHEC and VTEC strains. During the last few years, several new adhesins and putative colonisation factors have been described, especially in EHEC strains. Only a few adhesins (BfpA, AF/R1, AF/R2, Ral, F18 adhesins) appear to be host and pathotype specific. The others are found in more than one species and/or pathotype (EPEC, EHEC, VTEC). Initial adherence of EPEC, EHEC and VTEC strains to host cells is probably mediated by multiple mechanisms.  相似文献   

7.
Enteropathogenic (EPEC) and enterohemorrhagic (EHEC) Escherichia coli infections are characterised by the formation of attaching and effacing (AE) lesions on intestinal epithelial cells. Secretion of extracellular proteins (EspA, EspB, and EspD) via a type III secretion apparatus is necessary for the formation of the AE lesions by human EPEC. In this study, we show that bovine EPEC and EHEC are also able to secrete polypeptides homologous to the already described Esp proteins, most probably via a type III secretion system. Bovine EPEC and EHEC strains present two different secretion profiles of Esp proteins which correlate to the pathotypes of the esp genes as determined by PCR. We also demonstrate that genes encoding secreted proteins, present in the LEE of two bovine strains, are organised in the same way as in the human EPEC strain E2348/69.  相似文献   

8.
OBJECTIVE: To determine the prevalence and characteristics of attaching and effacing Escherichia coli (AEEC) in diarrheic and healthy small ruminants. ANIMALS: 502 lambs and kids with diarrhea and 511 healthy sheep and goats. PROCEDURE: Fecal samples from diarrheic and healthy sheep and goats were screened for the eae gene. In addition, E coli isolates with positive results for the eae gene (E coli eae+) were analyzed for the espB gene, production of verotoxins (VT), and serogroup. RESULTS: A significantly higher prevalence of healthy lambs and kids were infected with AEEC, compared with diarrheic lambs and kids and healthy adult sheep and goats. Some differences in the characteristics of E coli eae strains isolated from diarrheic and healthy animals were detected. Thus, the espB gene was detected more frequently among E coli eae+ strains isolated from healthy animals than in those isolated from diarrheic animals, and VT production was only detected in E coli eae+ strains isolated from healthy lambs and kids. The E coli eae+ isolates belonged to several O serogroups. However, 17 of 40 (42.5%) isolates from diarrheic lambs and only 4 of 168 (2.4%) isolates from healthy sheep belonged to serogroup 026. CONCLUSIONS AND CLINICAL RELEVANCE: Our results suggest that E coli eae+ 026 strains may play a role in diarrheal disease in lambs, whereas E coli eae+ strains that also had VT production and eae+ strains that had positive results for the espB gene did not appear to be associated with diarrhea in small ruminants.  相似文献   

9.
Feces of 70 diarrhoeic and 230 non‐diarrhoeic domestic cats from São Paulo, Brazil were investigated for enteropathogenic (EPEC), enterohaemorrhagic (EHEC) and enterotoxigenic (ETEC) Escherichia coli types. While ETEC and EHEC strains were not found, 15 EPEC strains were isolated from 14 cats, of which 13 were non‐diarrhoeic, and one diarrhoeic. None of 15 EPEC strains carried the bfpA gene or the EPEC adherence factor plasmid, indicating atypical EPEC types. The EPEC strains were heterogeneous with regard to intimin types, such as eae‐θ (three strains), eae‐κ (n = 3), eae‐α1 (n = 2), eae‐ι (n = 2), one eae‐α2, eae‐β1 and eae‐η each, and two were not typeable. The majority of the EPEC isolates adhered to HEp‐2 cells in a localized adherence‐like pattern and were positive for fluorescence actin staining. The EPEC strains belonged to 12 different serotypes, including O111:H25 and O125:H6, which are known to be pathogens in humans. Multi locus sequence typing revealed a close genetic similarity between the O111:H25 and O125:H6 strains from cats, dogs and humans. Our results show that domestic cats are colonized by EPEC, including serotypes previously described as human pathogens. As these EPEC strains are also isolated from humans, a cycle of mutual infection by EPEC between cats and its households cannot be ruled out, though the transmission dynamics among the reservoirs are not yet understood clearly.  相似文献   

10.
Detection and distribution of eae gene in forty-four attaching and effacing Escherichia coli (AEEC) strains of animal origin were investigated. Association of distinct intimin alleles with phylogenetic background were assessed among strains in comparison with different serogroups. Phylogenetic analysis showed that 31 EHEC/eae+ STEC strains belong to groups A, B1 and E, 13 EPEC strains segregated in B1 and B2. Moreover, group A possessed the eae gamma2/theta type, group B1 the eae beta1, eae kappa, eae zeta, and eae epsilon types, group B2 the eae alpha1, eae alpha2 and eae iota types, while the group E possessed the eae gamma1 type. The presence of numerous eae-types show that EPEC and EHEC/eae+ STEC tested have a high genetic homology within each phylogenetic group.  相似文献   

11.
Escherichia (E.) coli serotype O157:H7 is a globally distributed human enteropathogen and is comprised of microorganisms with closely related genotypes. The main reservoir for this group is bovine bowels, and infection mainly occurs after ingestion of contaminated water and food. Virulence genetic markers of 28 O157:H7 strains were investigated and multilocus enzyme electrophoresis (MLEE) was used to evaluate the clonal structure. O157:H7 strains from several countries were isolated from food, human and bovine feces. According to MLEE, O157:H7 strains clustered into two main clonal groups designated A and B. Subcluster A1 included 82% of the O157:H7 strains exhibiting identical MLEE pattern. Most enterohemorrhagic E. coli (EHEC) O157:H7 strains from Brazil and Argentina were in the same MLEE subgroup. Bovine and food strains carried virulence genes associated with EHEC pathogenicity in humans.  相似文献   

12.
Enteropathogenic Escherichia coli (EPEC), an important human pathogen has the ability to form attaching and effacing lesions on the intestinal epithelium and has been isolated from a wide range of species. Two EPEC subgroups are recognized: typical (tEPEC) and atypical (aEPEC) strains, differing by the presence of EAF plasmid and bundle-forming pilus (BFP) in typical strains and their absence in atypical strains. This study searched the presence of EPEC strains in 101 fecal samples of diarrheic (n=65) and non-diarrheic (n=36) dogs from two cities in Rio de Janeiro State, Brazil. The isolates were evaluated for the presence of eae, tir, espA, espB and bfpA genes, EAF plasmid, and for the insertion site of the LEE locus. Cell-adherence assays, fluorescent actin staining (FAS) test, hemolysin production and serotyping were also performed. Twenty eight aEPEC isolates were recovered from 48 eae-positive fecal samples, 24 from diarrheic animals and 4 from non-diarrheic ones. PCR showed that most isolates was positive for β or γ intimin, and for β or α subtypes of tir, espA and espB. Six isolates showed a selC insertion of locus LEE. Only two isolates from the same diarrheic animal harbored the bfpA gene, and none presented the EAF plasmid. Most isolates was FAS-positive and showed a localized adherence-like (LAL) in a 6h HeLa cell-adherence assay. A wide diversity of serotypes was detected including O4:H16 and O51:H40, previously described in human disease. The phenotypic and genotypic markers of aEPEC isolated from diarrheic and non-diarrheic dogs were similar to those found in isolates recovered from human disease.  相似文献   

13.
Of 273 samples (rectal swab) collected from free-ranging yaks of Tawang district, Arunachal Pradesh, 42 Shiga toxin-producing Escherichia coli (STEC), six enteropathogenic E. coli (EPEC) and 27 enterotoxigenic E. coli (ETEC) strains were isolated. All the STEC and EPEC strains were further investigated for respective stx variants (for STEC only) and additional putative virulence factors. The 27 ETEC strains were also screened for characteristic enterotoxin gene(s) and colonization factors. Occurrence of ETEC was significantly (p < 0.05) higher in the diarrheic yaks and yaks of less than 1 year of age. Majority of enterovirulent E. coli isolates were resistant to amikacin, azithromycin, chloramphenicol, colistin, doxycycline, furazolidone, nalidixic acid, nitrofurantoin, streptomycin and tetracycline. Dendrogram, constructed with molecular fingerprinting profiles obtained from RAPD (Randomly Amplified Polymorphic DNA) and ERIC (Enterobacterial Repetitive Intergenic Consensus) PCR, placed the isolates in different clusters irrespective of their serotypes, virulence gene and drug resistance pattern. Collectively, the study indicates that yaks, being a potential reservoir of multidrug resistant STEC and EPEC, may represent significant risk to public health in this region. Higher recovery of ETEC isolates from yaks with diarrhea points out that ETEC may be a major determinant for repeated occurrence of diarrhea in yaks.  相似文献   

14.
根据文献合成了一对引物,利用PCR方法检测了84株来自断奶仔猪水肿病例的产Vero细胞毒素大肠杆菌(VerotoxigenicEscherichiacoli,VTEC)的LEE(locusofenterocyteeffacement)毒力岛的eaeA基因,以了解携带LEE毒力岛的大肠埃希菌在江苏省断奶仔猪群VTEC中的流行状况。结果发现:从其中17株中可扩增到预期的DNA片断,证实它们携带LEE毒力岛,携带率为20.24%。数据分析提示:LEE毒力岛的分布不仅限于EPEC和EHEC,在断奶仔猪源VTEC中也有一定的分布,并可能成为重要的毒力因子。  相似文献   

15.
Many bacterial virulence attributes, like toxins, adhesins, invasins, iron uptake systems, are encoded within specific regions of the bacterial genome. These in size varying regions are termed pathogenicity islands (PAIs) since they confer pathogenic properties to the respective micro-organism. Per definition PAIs are exclusively found in pathogenic strains and are often inserted near transfer-RNA genes. Nevertheless, non-pathogenic bacteria also possess foreign DNA elements that confer advantageous features, leading to improved fitness. These additional DNA elements as well as PAIs are termed genomic islands and were acquired during bacterial evolution. Significant G+C content deviation in pathogenicity islands with respect to the rest of the genome, the presence of direct repeat sequences at the flanking regions, the presence of integrase gene determinants as other mobility features,the particular insertion site (tRNA gene) as well as the observed genetic instability suggests that pathogenicity islands were acquired by horizontal gene transfer. PAIs are the fascinating proof of the plasticity of bacterial genomes. PAIs were originally described in human pathogenic Escherichia (E.) coli strains. In the meantime PAIs have been found in various pathogenic bacteria of humans, animals and even plants. The Locus of Enterocyte Effacement (LEE) is one particular widely distributed PAI of E coli. In addition, it also confers pathogenicity to the related species Citrobacter (C.) rodentium and Escherichia (E.) alvei. The LEE is an important virulence feature of several animal pathogens. It is an obligate PAI of all animal and human enteropathogenic E. coli (EPEC), and most enterohaemorrhegic E. coli (EHEC) also harbor the LEE. The LEE encodes a type III secretion system, an adhesion (intimin) that mediates the intimate contact between the bacterium and the epithelial cell, as well as various proteins which are secreted via the type III secretion system. The LEE encoded virulence features are responsible for the formation of so called attaching and effacing (AE) lesions in the intestinal epithelium. Due to its wide distribution in animal pathogens, LEE encoded antigens are suitable vaccine antigens. Acquisition and structure of the LEE pathogenicity island is the crucial point of numerous investigations. However, the evolution of the LEE, its origin and further spread in E. coli, are far from being resolved.  相似文献   

16.
A longitudinal study (cohort study) elaborating 1,224 rectal swabs from 221 calves aging between 1 and 12 weeks was conducted on 11 dairy farms (i) to ascertain associations between diarrhea and shedding of diarrheagenic E. coli and (ii) to facilitate the zoonotic potential assessment of E. coli strains shed by young calves. Calves were screened weekly by PCR of swab cultures for shedding of enterotoxigenic E coli [ETEC; by detection of heat stable (est) and heat labile enterotoxin genes (elt)], diffusely adhering E. coli [DAEC; diffuse adhesion (daa)], typical enteropathogenic E. coli [EPEC; bundle-forming pili (bfpA) and intimin (eae)] as well as enterohemorrhagic E. coli [EHEC, intimin (eae) and Shiga toxin (stx)]. In addition, EHEC-hemolysin- (Hly(EHEC)) and alpha-hemolysin- (alpha-Hly) producing E. coli were detected by inoculation of blood agar plates. Within the 221 calves, prevalences were 69.7% (25.2% of the 1,224 samples) for Hly(EHEC)-producing E. coli, 55.3% (19.3%) for eae, and 18.2% (4.5%) for stx. E. coli strains exhibiting an alpha-Hly phenotype were detected in 66.5% of the calves and 21.9% of fecal samples. The est gene was detectable in 31.7% of the calves from only 9 of 11 herds and in 7.8% of the samples. Calves shedding DAEC or typical EPEC were not identified. The detection frequency of virulence traits significantly depended on the calves' age and shedding dynamics differed between the traits. A significant correlation between calf diarrhea and shedding of EHEC virulence traits was determined for several postnatal periods (1 week: Hly(EHEC); 1st & 10th week: eae; 4th week stx). Shedding of ETEC (est) was associated with diarrhea in newborn calves (1st week) only. Hly(EHEC)- and alpha-Hly-producing E. coli were shed significantly more frequently by diarrheic calves in 1st and 8th week of life, respectively. The knowledge gained in this study highlights the high prevalence of zoonotic E. coli already in calves.The age-dependent shedding dynamic of the various E. coli pathovars has to be considered regarding prophylaxis as well as planning intervention studies, both for calves and humans.  相似文献   

17.
A total of 206 attaching and effacing Escherichia coli strains from ruminants were analysed for the presence of the astA (EAST1) and bfpA genes. None of these strains was bfpA-positive. The percentage of enteropathogenic E. coli (EPEC) strains astA-positive found in healthy cattle (15.6%) suggests that this animal species may be a significant reservoir of atypical EPEC potentially pathogenic for humans.  相似文献   

18.
This study was conducted to determine the prevalence and characteristics of pathogenic Escherichia (E.) coli strains from diarrheic calves in Vietnam. A total of 345 E. coli isolates obtained from 322 diarrheic calves were subjected to PCR and multiplex PCR for detection of the f5, f41, f17, eae, sta, lt, stx1, and stx2 genes. Of the 345 isolates, 108 (31.3%) carried at least one fimbrial gene. Of these 108 isolates, 50 carried genes for Shiga toxin and one possessed genes for both enterotoxin and Shiga toxin. The eae gene was found in 34 isolates (9.8%), 23 of which also carried stx genes. The Shiga toxin genes were detected in 177 isolates (51.3%) and the number of strains that carried stx1, stx2 and stx1/stx2 were 46, 73 and 58, respectively. Among 177 Shiga toxin-producing E. coli isolates, 89 carried the ehxA gene and 87 possessed the saa gene. Further characterization of the stx subtypes showed that among 104 stx1-positive isolates, 58 were the stx1c variant and 46 were the stx1 variant. Of the 131 stx2-positive strains, 48 were stx2, 48 were stx2c, 11 were stx2d, 17 were stx2g, and seven were stx2c/stx2g subtypes. The serogroups most prevalent among the 345 isolates were O15, O20, O103 and O157.  相似文献   

19.
We investigated the clonal relationships among 41 enterotoxigenic (ETEC) or non-enterotoxigenic (NETEC) Escherichia coli strains producing the F17 a fimbriae isolated from diarrheic calves in France or Belgium in the early 1980s. Twenty-three of the 26 ETEC strains were highly clonally related, most of them with a O101:K32:H9-serotype. The NETEC strains were also divided in clonal subgroups, most of them with O101:H-serotype. The F17 a positive ETEC strains are no longer isolated from diarrheic calves in these countries. It is postulated that the use of a vaccine including O101, K32 and H9 antigens in addition to K99 (F5) explains the strongly reduced isolation of the O101:K32:H9, K99 (F5) E. coli clone.  相似文献   

20.
F17 fimbriae are produced by pathogenic Escherichia coli involved in diarrhea and septicemia outbreaks in calves and lambs. These proteins result from the expression of four different clustered genes, namely f17A, f17D, f17C and f17G, encoding a pilin protein, a periplasmic protein, an anchor protein and an adhesin protein, respectively. Several variants of f17A and f17G genes have been reported and found genetically associated with typical virulence factors of bovine pathogenic E. coli strains. In this study, a new F17e-A variant, closely related to F17b-A, was identified from a collection of 58 E. coli isolates from diarrheic calves in Iran. While highly prevalent in Iranian F17-producing clinical isolates from calves, this variant was rare among E. coli from a French healthy adult bovine population, suggesting a possible association with virulence. The f17Ae gene was also found in the genome of the Shiga-like toxin variant Stx1d–producing bovine E. coli strain MHI813, and belonged to a gene cluster also encoding a new F17-G3 variant, which greatly differed from F17-G1 and F17-G2. This gene cluster was located on a pathogenicity island integrated in the tRNA pheV gene. The gene coding for a third new F17f-A variant corresponding to a combination of F17c-A and F17d-A was also identified on the pVir68 plasmid in the bovine pathogenic E. coli strain 6.0900. In conclusion, we identified three new F17-A and F17-G variants in cattle E. coli, which may also have significant impact on the development of new diagnostics and vaccination tools.  相似文献   

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