Spread of multidrug-resistant IncHI1 plasmids carrying ESBL gene blaCTX-M-1 and metabolism operon of prebiotic oligosaccharides in commensal Escherichia coli from healthy horses, France.

This research aims to understand the spread of a drug-resistant bacterium called Escherichia coli in healthy horses across France, with a particular focus on specific genetic elements in the bacterium that resist certain antibiotics and can metabolize prebiotic oligosaccharides. The researchers found that drug-resistant E. coli was present in around 8.5% of horses sampled, and that certain forms of resistance-carrying genetic elements, or plasmids, were particularly prevalent.

Research Methods and Goals

• The researchers collected faecal samples from 744 adult horses from 41 stables to examine the presence and characteristics of Escherichia coli resistant to Expanded-spectrum cephalosporin (ESC), a class of antibiotic.
• By using a variety of molecular biology techniques, such as polymerase chain reaction (PCR) and DNA sequencing, specific resistance genes were identified, and the transfer type, namely conjugation (direct transfer between bacteria) or transformation (uptake from the environment), was determined.
• The researchers further classified these E. coli isolates through various typing methods, including PCR-based replicon typing, restriction fragment length polymorphism (RFLP), and plasmid multilocus sequence typing (pMLST).
• The aim was to comprehend the spread and frequency of drug-resistant E. coli in healthy horses and identify the particular genetic determinants responsible for this resistance.

Findings and Implications

• The data showed that around 8.5% of the tested horses carried ESC-resistant E. coli. The E. coli strains were mainly of the B1 phylogroup and did not carry major virulence genes, indicating they are commensal (harmlessly co-existing with the horse).
• The dominant resistance mechanism was through the Extended Spectrum Beta-Lactamase (ESBL) bla genes which were often found on conjugative plasmids – mobile genetic elements that bacteria use to share genes.
• Importantly, the researchers found that these resistance genes were commonly found on the multidrug-resistant IncHI1-pST9 plasmids, which also carried genes for the metabolism of short-chain fructo-oligosaccharides (scFOS), a type of prebiotic.
• This dual presence poses a potential risk if scFOS are used as prebiotics in horse feed, as their consumption could promote the survival and spread of these multidrug-resistant plasmids in the gut microbiota of horses.
• The study thus underscores the need for careful consideration of prebiotic use in managing livestock health to prevent promoting antibiotic resistance among commensal bacteria.