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Danish researchers have found evidence that pigs can spread dangerous antibiotic-resistant superbug Clostridioides difficile to humans.
A team from the University of Copenhagen and Statens Serum Institut in Denmark found samples of the superbug C.difficile more commonly in piglets and sows than slaughter pigs across 14 pig farms in Denmark.
The difference may be due to the younger pigs having a microbiota composition that makes them more susceptible to a successful colonisation, the researchers said.
C. difficile is a bacterium that infects the human gut and is resistant to all but three current antibiotics. Some strains contain genes that allow them to produce toxins that can cause damaging inflammation in the gut, leading to life-threatening diarrhoea, mostly in the elderly and hospitalised patients who have been treated with antibiotics.
"Our finding of multiple and shared resistance genes indicate that C. difficile is a reservoir of antimicrobial resistance genes that can be exchanged between animals and humans," said Dr. Semeh Bejaoui from the varsity.
"This alarming discovery suggests that resistance to antibiotics can spread more widely than previously thought, and confirms links in the resistance chain leading from farm animals to humans," Bejaoui added.
The study was presented at this year's European Congress of Clinical Microbiology and Infectious Diseases (ECCMID) being held in Portugal. In the study, the team investigated the prevalence of C. difficile strains in livestock (pigs) and the potential for zoonotic spread of antimicrobial resistance genes by comparing to clinical isolates from Danish hospital patients.
Stool samples were collected from 514 pigs in two batches from farms across Denmark between 2020 and 2021. Batch A included 330 samples from sows, piglets and slaughter pigs from fourteen farms in 2020. The 184 samples in batch B were collected during slaughtering in 2021.
Out of 514 pigs samples, 54 had evidence of C. difficile. Further analyses of 40 samples, found that C. difficile was more common in piglets and sows than slaughter pigs. The researchers speculate that this may be due to the difference in age between piglets and adult pigs -- with the younger pigs having a microbiota composition that makes them more susceptible to a successful colonisation.
In total, thirteen sequence types found in animals matched those found in patient's stool samples. ST11, an animal-associated strain, was the most common. In sixteen cases, ST11 strains in humans and animals were identical.
All isolates from animals were positive for the toxin genes and ten were also hypervirulent, with an even greater capacity to cause disease.
In total, 38 isolates from the animals contained at least one resistance gene and overall, resistance was predicted for seven classes of antibiotics, of which the most common were macrolides, beta-lactams, aminoglicosides and vancomycin -- which are important for treating severe bacterial infections.
The team blamed the overuse of antibiotics in human medicine and as cheap production tools on farms affecting efforts to cure bacterial infections.
"Of particular concern is the large reservoir of genes conferring resistance to aminoglycosides, a class of antibiotics to which C. difficile is intrinsically resistant -- they are not needed for resistance in this species. C. difficile thus plays a role in spreading these genes to other susceptible species," Bejaoui said.
