Evaluation of Virulence Profiles of Environmental Avian Pathogenic Escherichia coli O157 Isolates

Introduction: Bacterial pathogens may pick up virulence factors that alter their phenotype. Such was the case with the novel STEC E.coli O104:H4 which caused a large outbreak associated with sprouted seeds. Avian pathogenic E. coli (APEC) may contain an array of virulence factors. Poultry litter is often composted to be used as fertilizer for agricultural crops and fields. Because poultry litter and poultry may be reservoirs of APEC, this may be important for public health and food safety.

Purpose: The pathogenic mechanisms of APEC which cause disease in poultry may also contain virulence factors important to causing human infections. An avian model was used to assess the relationship between clinical phenotypes and the genotypic virulence profiles of APEC isolates. Fecal shedding by APEC was determined, which is important given APEC are traditionally a respiratory problem in broilers.

Methods: Two-week old broilers were orally inoculated with 8 O157 APEC isolates containing genes important for protease activity, hemolysis, and attachment (ehxA, espP, katP, stcE). Cloacal swabs were collected over 4-weeks post-inoculation. Fecal shedding of APEC was quantified on Sorbitol MacConkey agar (SMAC) and confirmed by molecular detection. Control birds were sham inoculated with TSB.

Results: Birds did not shed APEC pre-inoculation, but all 8 groups (n=24) were positive for fecal-shedding of APEC by day 27 post-inoculation. E. coli strains with ehxA were shed at 2 dpi on the scale of 10⁶ CFU. Hemolysin activity appeared most important as determined by PCR on virulent APEC strains. Necropsies on deceased birds or those culled due to clinical illness showed signs of extreme hemolysis. APEC O157 isolates showed varying clinical phenotypes in birds. Symptoms included ruffled feathers, labored breathing, bloated intestines, hemorrhaged breast muscle, ascites, and diarrhea.

Significance: APEC that are stx negative were extremely virulent in broilers and appear to be shed in feces. APEC genotype may not dictate phenotypic profiles as seen here in live birds. This is being assessed in Caco-2 cells as well.