Pigs Can Spread Deadly Antibiotic-Resistant Superbugs to Humans, Study Finds
Fears of antibiotic-resistant superbugs caused by animal agriculture escalate as new study reveals evidence that a dangerous superbug strain can jump from pigs to humans.
Credit: Andrew Skowron
Scientists have discovered “alarming” evidence of deadly superbugs that can spread from pigs to humans, according to new research.
Analysis by Semeh Bejaoui and Dorte Frees of Copenhagen University and Soren Persson at Statens Serum Institute in Denmark investigated the superbug Clostridioides difficile, which is considered one of the world’s most significant antibiotic resistance threats.
“Our finding indicates that C.difficile is a reservoir of antimicrobial resistance genes that can be exchanged between animals and humans,” said Bejaoui, who is due to present her study at the European Congress of Clinical Microbiology & Infectious Diseases in Lisbon on Sunday. “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.”
C. difficile 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 diarrhea, mostly in the elderly and hospitalized patients. In the U.S., C. difficile caused an estimated 223,900 infections and 12,800 deaths in 2017, costing the healthcare system more than $1 billion.
With experts predicting that antibiotic-resistant infections will kill more people than cancer in less than three decades, antibiotic resistance is one of the greatest challenges affecting modern medicine today.
Experts have repeatedly warned that the use of antibiotics on farmed animals is extremely dangerous to human health, but the practice remains widespread around the world, with two-thirds of all antibiotics sold for livestock production.
In particular, the rise of factory farms in the U.S. has seen an increase in the use of antibiotics, with the animals pumped full of medicine to make them grow quicker and to keep them alive for longer.
This practice risks creating a potentially devastating human resistance to antibiotics. The United Nations (UN) has repeatedly warned that antibiotic-resistant bacteria is increasing: at least 750,000 people die every year from drug-resistant diseases, and the UN says that number could increase to 10 million deaths annually by 2050 if no action is taken.
In their research, the team led by Bejaoui focused on investigating the prevalence of C. difficile in farm animals. In this case, pigs were studied and results were compared with clinical isolates from Danish hospital patients to see if there was a match in humans. Samples were screened for the presence of C. difficile and genetic sequencing was used to identify whether they harbored toxin and drug resistance genes.
In this study, the scientists investigated samples of C. difficile strains in pigs from more than 14 farms in Denmark and compared the results with those from Danish hospital patients. The researchers used the samples to see if toxin and antibiotic-resisting genes were present in both pigs and humans, something that increases the potential for zoonotic transmission of more drug-resistant strains of C. difficile.
“We found that the strains isolated in pigs were genetically identical to the ones found in humans over the same period,” said Bejaoui. “We have still to show that the strains were passed from pigs to humans but what our study does make clear is that farms that use antibiotics are creating conditions which allow resistant strains to flourish and these will ultimately infect humans.
“Of particular concern is the large reservoir of genes conferring resistance to aminoglycosides, a class of antibiotics to which C.difficile is intrinsically resistant. It thus plays a role in spreading these genes to other susceptible species. This study provides more evidence on the evolutionary pressure connected with the use of antimicrobials in animal husbandry, which selects for dangerously resistant human pathogens.”
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