Introduction: Enterotoxigenic E. coli are a major cause of diarrhoea in humans and animals around the world, and understanding how these pathogens cause disease and evade treatment is an important step in reducing their impact on society, both medically and economically. It is also important to determine if there is a genetic basis for zoonosis, where pathogens spread from an animal population into a human population. In this study, we aimed to characterise the virulence and antibiotic resistance regions of two important porcine enterotoxigenic E. coli isolates taken from pig farms in Australia.

Methods:  Characterisation of both isolates was performed through the use of PCR, Next Generation sequencing and analysis using bioinformatics tools. Antibiotic resistance regions were analysed through the generation of a fosmid library.

Results: The presence of multiple toxins, including the heat stable enterotoxins east1, STa and STb, the alpha-hemolysin hlyA, and the heat-labile enterotoxin gene eltB was confirmed. Enterotoxigenic adhesins such as the K88 (F4) fimbrial adhesin, the ᴅ-mannose specific adhesin fimH and a highly conserved adhesin eaeH were positively identified along with other genes relating to iron uptake, serum survival and phylogenetic grouping. The isolate contained multiple antibiotic resistance regions, with multiple gene cassettes present.  Genes conferring antibiotic resistance to streptomycin, spectinomycin, trimethoprim, sulphonamides and streptothricin were identified in two separate class 1 integrons. These integrons were associated with Tn21, Tn1721, IS26 and an IS1133 element containing an IS903 insertion. A third class 1 integron region has been inferred from PCR and sequence data, as well as a class 2 integron associated with Tn7.

Conclusion: This study showed that both of these porcine O157 ETEC isolates contain a plethora of phage associated virulence genes as well as several complex and potentially mobile antibiotic resistance regions.