Correlating genetic and phenotypic characteristics in avian pathogenic Escherichia coli as a model environmental pathogen
Date
2013
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Publisher
University of Delaware
Abstract
Avian pathogenic E .coli (APEC) isolates are widespread in poultry flocks and cause colibacillosis in birds resulting in severe economic losses every year in the U.S. APEC is part of the group of extraintestinal pathogenic E. coli (ExPEC), a group which causes a wide variety of diseases in both animals and humans. Although APEC is not normally associated with enterohemorraghic E. coli (EHEC), there have been recent reports linking APEC with human disease and the finding of stx1 and stx2 genes in APEC may increase this risk. Also, APEC strains are closely related to human uropathogenic E.coli (UPEC), which could be a separate cause for concern.
Bacterial pathogens may pick up virulence factors that change their genotype and thus alter their phenotype. Such was the case with the novel STEC E. coli O104:H4 which caused a large outbreak associated with sprouted Fenugreek seeds. APEC may contain an array of virulence factors, some potentially hazardous to public health. Because APEC isolates can be isolated from a range of retail foods and have the potential to be a zoonotic risk, there is a growing concern of APEC contamination in our food supply.
The purpose of this study was to characterize APEC strains isolated from poultry flocks in Delaware and better understand their role in causing foodborne diseases and acting as a zoonotic agent. Three-hundred and twenty APEC strains had been earlier isolated from lesions in diseased poultry on the Delmarva peninsula. These APEC strains spanned a wide variety of O-types including O157 and were isolated from a numerous different types of lesions. A total of 100 APEC isolates consisting of a variety of O-types and lesion locations were chosen for further use in this study.
The 100 APEC isolates were screened for eight different EHEC virulence genes which included stx1, stx2, eaeA, espA, katP, espP, stcE, and ehxA. A total of 28 APEC isolates possessed one gene each, with none of them having stx1 or stx2 and only one of them having eaeA. The 100 isolates were also screened for seven different ExPEC virulence genes which included iss, iucD, papC, astA, vat, tsh, and cva/cvi. A total of 87 APEC isolate possessed one to five of these genes. A challenge study was performed on a flock of 30 broilers to determine if the APEC infected birds would shed the bacteria in their feces. It could not be determined that the broilers were shedding APEC in their feces, because inconclusive evidence was found to support this claim.
The 28 APEC strains shown to possess an EHEC gene were chosen for further evaluation via two attachment assays. The first trial quantified the level of APEC to strongly attach to retail chicken meat. The APEC isolates attached at a wide variety of levels, but a total of five isolates all attached more strongly than both E. coli O157:H7 and O104:H4. The second trial tested the amount of bacteria to attach to the HCT-8 human intestinal cell-line. Again the APEC had a wide array of attachment abilities, but ten isolates were able to attach at a higher level than both of the E. coli outbreak strains.
The two attachment assays showed that many of the APEC isolates were able to attach at a level significantly higher than E. coli strains involved in large outbreaks. This shows that with the acquisition of additional EHEC virulence genes or even with the ExPEC virulence genes they currently possess, that APEC may be a zoonotic risk. However, persistence through the farm to fork continuum must still be researched.