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Antibiotic-resistant superbug found in pigs and humans: a study

Researchers studying the C. difficile superbug claim that its antibiotic resistance genes have been found in pigs and humans, which means that not only is bacterial transmission possible on a larger scale, but antibody-resistant genes themselves can spread an animal vector to humans. .

Clostridioides difficile or C. difficile is a bacterium that causes intestinal infections, causes symptoms such as diarrhea and inflammation of the colon, and is resistant to many antibiotics. Some strains have genes that allow them to cause extreme damage, and this can be life-threatening, especially in elderly patients who receive antibiotics due to other problems.

It is also considered one of the world’s most significant threats to antibiotic resistance. In 2017, C. difficile caused more than 223,000 cases, 12,800 deaths and cost $ 1 billion in healthcare costs in the United States, according to the US Centers for Disease Control and Prevention. A Canadian study found that between 2009 and 2015, more than 20,600 adults reported C. difficile infection that developed in a medical setting.

“Our findings of multiple and shared resistance genes suggest that C. difficile is a reservoir of antimicrobial resistance genes that can be exchanged between animals and humans,” Dr. Semeh Bejaoui, a doctoral student at the University of Copenhagen and one of the authors of the study, said in a press release. “This alarming discovery suggests that antibiotic resistance may spread more than previously thought, and confirms the links in the resistance chain from livestock to humans.”

C. difficile does live in the intestines of many people as part of the regular balance of the digestive system, but its growth is normally kept under control by other bacteria.

The dangerous side of C. difficile can be unlocked by a common tool in the health system: antibiotics.

When a person takes antibiotics to deal with an infection, the drug destroys some of the other bacteria in the gut as well as the infection he targeted – and because C. difficile is resistant to antibiotics, if the balance of the intestinal system is discarded, C. difficile can slip out. control and attack the lining of the intestines. Recent antibiotic use is the biggest risk factor for developing inflammation or C. difficile infection.

The researchers wanted to find out whether C. difficile strains, which are known to have antibiotic resistance genes as well as toxin-producing genes, were present in both pigs and humans, which could suggest that zoonotic transmission helps C. difficile develop into more dangerous forms and spread faster.

In a study presented this week at the European Congress of Clinical Microbiology & Infectious Diseases in Portugal, researchers examined C. difficile samples on 14 pig farms in Denmark and compared these samples with samples from Danish hospital patients.

They looked at stool samples from 514 pigs taken between 2020 and 2021 and found that 54 pigs had C. difficile. They then used genetic sequencing to isolate strains that had increased numbers of toxin-producing genes and drug resistance. All samples from 54 pigs had toxin-producing genes.

The researchers compared the results from pigs with 934 isolates from human patients who had been infected with C. difficile during this time.

Thirteen types of sequences matched between porcine and human patients, with animal-associated strain ST11 being the most common. In 16 cases, strain ST11 was identical in humans and animals.

Of the 54 pig samples, 38 had at least one antibiotic resistance gene, and resistance generally related to a class of antibiotics commonly used to treat severe bacterial infections.

The researchers believe this suggests that the use of antibiotics in livestock has the unintended side effect of producing more hypervirulent C. difficile strains that could be capable of being transmitted to humans via zoonotic transmission.

“The overuse of antibiotics in human medicine and as cheap production tools on farms is destroying our ability to cure bacterial infections,” Bejaoui said.

Experts have highlighted the problem of antibiotic overuse in livestock before – in August 2021, the UN issued a joint statement with the Global Leaders Group on Antimicrobial Resistance, calling for a significant reduction in antimicrobials in food production and livestock, warning that “the world is moving fast breaking point, when the antimicrobials they rely on to treat infections in humans, animals and plants will no longer be effective.

Bejaoui added that the researchers were interested in finding out that some strains of C. difficile have many other antibiotic resistance genes that no longer affected the bacterium.

“Of particular concern is the large reservoir of genes conferring resistance to aminoglycosides, a class of antibiotics to which C. difficile is internally resistant – they are not needed for resistance in this species. C. difficile thus plays a role in the spread of these genes to other susceptible species, “she said.

“This study provides further evidence of the evolutionary pressure associated with the use of antimicrobials in animal husbandry, which selects dangerously resistant human pathogens. This underlines the importance of adopting a more comprehensive approach to the treatment of C. difficile infection in order to consider all possible routes of spread. “

One of the major limitations of the study is that while the researchers found similar strains of the bacterium in both pigs and humans, they were unable to determine the direction of potential transmission – that is, whether the bacterium could jump from animal to human, human to animal, or both.

“The fact that some strains in human and animal isolates were identical suggests that they could be shared between groups, but until we perform deeper phylogenetic analyzes, we cannot determine the direction of transmission, which could also be two-way, with bacteria. they are constantly being exchanged and disseminated in the community and on farms, ”said Bejaoui.