Assessment of commensal Escherichia coli as inhibitors of Escherichia coli O157:H7 through production of antimicrobial peptides and nutrient competition

Authors: Maki, Joel

Submitted to: American Society for Microbiology
Publication Type: Abstract Only
Publication Acceptance Date: 2/28/2024
Publication Date: N/A
Citation: N/A

Interpretive Summary:

Technical Abstract: Escherichia coli O157:H7 continues to represent a major food safety concern, making the development of interventions to reduce or eliminate O157:H7 in food products an imperative. One potential intervention strategy is the reduction or elimination of O157:H7 in cattle, its main reservoir, through the utilization of probiotics. The commensal E. coli populating the cattle intestine represent a compelling source of probiotics, as these organisms are, presumably, already well-adapted to colonizing the bovine gastrointestinal tract. The challenge is to identify candidate strains capable of competing with O157:H7 for nutrients or producing bacteriocins, a type of antimicrobial peptide, to inhibit O157:H7 growth. There are several nutrients O157:H7 utilizes for in vivo growth which appear infrequently utilized by other commensal E. coli. These include ethanolamine, galactose, mannose, ribose, and hexuronates such as gluconate and glucoronate. E. coli strains may also produce bacteriocins, some of which inhibit O157:H7. Here, E. coli from fecal samples and recto-anal junction swabs of healthy cattle were isolated, sequenced, and screened for the ability to compete with O157:H7 using both genomics-based and in vitro approaches. Average nucleotide identity (ANI) analysis identified 14 genetically distinct (ANI < 99.9%) commensal E. coli isolates. The Bagel4 web server was used to screen E. coli isolate genomes for bacteriocins and ribosomally synthesized and post-translationally modified peptides. Multiple categories of bacteriocins were identified across isolate genomes, including the gene for colicin 1b, a potential inhibitor of O157:H7. The metabolism-focused genome annotator DRAM identified several metabolic pathways in the commensal E. coli, including those for galactose and mannose utilization, suggesting these strains could be capable of competing with O157:H7 for required substrates. The DRAM findings were largely confirmed in vitro, with all 14 strains capable of fermenting mannose and galactose, along with ribose and gluconate. Together, these results suggest cattle harbor E. coli strains which could compete with O157:H7 either nutritionally or through production of bacteriocins. Surveys of commensal E. coli populations from cattle, using methods like those described here, can identify probiotic candidates capable of outcompeting O157:H7 in the bovine intestinal tract, reducing O157:H7 contamination in the supply chain and increasing food safety.