Isolation from a sheep of an attaching and effacing Escherichia coli O115:H- with a novel combination of virulence factors

Attaching and effacing (AE) lesions were observed in the caecum, proximal colon and rectum of one of four lambs experimentally inoculated at 6 weeks. of age with Escherichia coli O157:H7. However, the attached bacteria did not immunostain with O157-specific antiserum. Subsequent bacteriological analysis of samples from this animal yielded two E. coli O115:H- strains, one from the colon (CO) and one from the rectum (RC), and those bacteria forming the AE lesions were shown to be of the O115 serogroup by immunostaining. The O115:H(-)isolates formed microcolonies and attaching and effacing lesions, as demonstrated by the fluorescence actin staining test, on HEp-2 tissue culture cells. Both isolates were confirmed by PCR to encode the epsilon (epsilon) subtype of intimin. Supernates of both O115:H- isolates induced cytopathic effects on Vero cell monolayers, and PCR analysis verified that both isolates encoded EAST1, CNF1 and CNF2 toxins but not Shiga-like toxins. Both isolates harboured similar sized plasmids but-PCR analysis indicated that only one of the O115:H- isolates (CO) possessed the plasmid-associated virulence determinants ehxA and etpD. Neither strain possessed the espP, katP or bfpA plasmid-associated virulence determinants. These E. coli O115:H- strains exhibited a novel combination of virulence determinants and are the first isolates found to possess both CNF1 and CNF2.

Comparative genomic indexing reveals the phylogenomics of Escherichia coli pathogens

The Escherichia coli O26 serogroup includes important food-borne pathogens associated with human and animal diarrheal disease. Current typing methods have revealed great genetic heterogeneity within the O26 group; the data are often inconsistent and focus only on verotoxin (VT)-positive O26 isolates. To improve current understanding of diversity within this serogroup, the genomic relatedness of VT-positive and -negative O26 strains was assessed by comparative genomic indexing. Our results clearly demonstrate that irrespective of virulence characteristics and pathotype designation, the O26 strains show greater genomic similarity to each other than to any other strain included in this study. Our data suggest that enteropathogenic and VT-expressing E. coli O26 strains represent the same clonal lineage and that W-expressing E. coli O26 strains have gained additional virulence characteristics. Using this approach, we established the core genes which are central to the E. coli species and identified regions of variation from the E. coli K-12 chromosomal backbone.

The occurrence of treponemes in contagious ovine digital dermatitis and the characterisation of associated Dichelobacter nodosus

Contagious ovine digital dermatitis (CODD) is a recently recorded, apparently new infection of the ovine hoof, which differs clinically from footrot caused by Dichelobacter nodosus and which fails to respond well to accepted treatment practices for footrot. Despite the welfare implications of such an infection, very little research has been performed on CODD to date and the aetiology remains confused. Suggestions have been made that there is a potential role for treponemes in the pathogenesis of CODD but that D. nodosus is apparently not involved. Six farms were therefore targeted in this study to provide a more in-depth investigation into the bacterial flora of CODD lesions. Dark ground microscopy, culture and PCR techniques were used, concentrating on the presence of D. nodosus and spirochaetes, particularly those of the genus Treponema. The results demonstrated that isolates of D. nodosus were indeed present in a high percentage (74%) of CODD lesions compared with 31% of apparently healthy feet. The isolates were shown to be of similar virulence type to those reported previously in cases of footrot, and the range of serogroups was also found to be similar to footrot, with serogroup H being prevalent. Treponemes were present in 70% of CODD lesions and 38% of apparently healthy feet, supporting a possible association between CODD and treponemes. However, any further progress on the aetiology of CODD and the potential for novel, effective treatment will depend on an improved ability to culture these organisms routinely in the laboratory thereby enabling their complete characterisation. (c) 2005 Elsevier B.V. All rights reserved.