Abstract
Extraintestinal pathogenic Escherichia coli (ExPEC) strains are important pathogens that cause diverse diseases in humans and poultry. Some E. coli isolates from chicken feces contain ExPEC-associated virulence genes, so appear potentially pathogenic; they conceivably could be transmitted to humans through handling and/or consumption of contaminated meat. However, the actual extraintestinal virulence potential of chicken-source fecal E. coli is poorly understood. Here, we assessed whether fecal E. coli isolates from healthy production chickens could cause diseases in a chicken model of avian colibacillosis and three rodent models of ExPEC-associated human infections. From 304 E. coli isolates from chicken fecal samples, 175 E. coli isolates were screened by PCR for virulence genes associated with human-source ExPEC or avian pathogenic E. coli (APEC), an ExPEC subset that causes extraintestinal infections in poultry. Selected isolates genetically identified as ExPEC and non-ExPEC isolates were assessed in vitro for virulence-associated phenotypes, and in vivo for disease-causing ability in animal models of colibacillosis, sepsis, meningitis, and urinary tract infection. Among the study isolates, 13% (40/304) were identified as ExPEC; the majority of these were classified as APEC and uropathogenic E. coli, but none as neonatal meningitis E. coli. Multiple chicken-source fecal ExPEC isolates resembled avian and human clinical ExPEC isolates in causing one or more ExPEC-associated illnesses in experimental animal infection models. Additionally, some isolates that were classified as non-ExPEC were able to cause ExPEC-associated illnesses in animal models, and thus future studies are needed to elucidate their mechanisms of virulence. These findings show that E. coli isolates from chicken feces contain ExPEC-associated genes, exhibit ExPEC-associated in vitro phenotypes, and can cause ExPEC-associated infections in animal models, and thus may pose a health threat to poultry and consumers.
Highlights
The primary and secondary habitats of Escherichia coli are the intestinal tract of warm-blooded animals and the environment, respectively
Based on the host and the site of infection, different Extraintestinal pathogenic E. coli (ExPEC) strains are subclassified as neonatal meningitis E. coli (NMEC), sepsis-associated E. coli (SEPEC), uropathogenic E. coli (UPEC), which cause newborn meningitis, sepsis, and urinary tract infections (UTI), respectively; and avian pathogenic E. coli (APEC), which mainly causes respiratory and systemic disease in poultry
Virulence of chicken fecal E. coli isolates performed in dedicated animal facilities in accordance with protocols approved by the Arizona State University (ASU) or Iowa State University (ISU) Institutional Animal Care and Use Committee (ASU Protocol number 1168R and ISU Protocol number 1-16-8159G)
Summary
The primary and secondary habitats of Escherichia coli are the intestinal tract of warm-blooded animals and the environment, respectively. Many E. coli strains are harmless commensals, a subset have acquired the ability to cause intestinal or extraintestinal diseases. Extraintestinal pathogenic E. coli (ExPEC) strains cause diverse infections outside of the intestinal tract in humans and animals [3,4,5]. Based on the host and the site of infection, different ExPEC strains are subclassified as neonatal meningitis E. coli (NMEC), sepsis-associated E. coli (SEPEC), uropathogenic E. coli (UPEC), which cause newborn meningitis, sepsis, and urinary tract infections (UTI), respectively; and avian pathogenic E. coli (APEC), which mainly causes respiratory and systemic disease in poultry. ExPEC strains can colonize the intestine, similar to non-pathogenic commensal E. coli [3, 6], but are equipped with virulence factors that allow them to cause disease in extraintestinal sites. In addition to the intestine, poultry houses serve as a reservoir for APEC [7], and this environment allows strains to persist for many months over successive flocks [8]
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