The role of food in Clostridioides difficile transmission chains still needs to be clarified, according to a study.

Clostridioides difficile infection (CDI) is a notable cause of infectious diarrhea worldwide.

Human-to-human transmission plays a major role, but other infection sources and routes are under investigation. Clostridioides difficile has been isolated from various foods and experts believe it is feasible that some of them could be important vectors for its widespread dissemination.

Existing evidence suggests that potatoes, which represent a major staple food consumed worldwide, could contribute to the spread of Clostridioides difficile. They have the highest contamination rates among vegetables tested to date. Confirmed cases of food-associated CDI have not yet been described.

COMBACTE-CDI (Combatting Bacterial Resistance in Europe) is a European consortium of experts from eight academic and research organizations plus six industrial partners.

One piece of work includes providing up-to-date information on Clostridioides difficile in food across Europe. To do this, the consortium collected clinical, animal and food samples in 12 countries. Results were published in the journal Eurosurveillance.

Potatoes were sampled from Poland, Romania, Slovakia, Austria, France, Netherlands the United Kingdom, Ireland, Sweden, Greece, Italy and Spain between January and July 2018. The number of samples in each nation ranged from six in Ireland to 29 in the UK and they were collected from five to 20 retailers per country.

Role of positive potatoes in infection
Overall, 33 of 147 samples tested positive for Clostridioides difficile. All nine samples from Slovakia were negative and all seven from Romania were positive. Positivity rates across countries varied substantially.

Only 13 potato samples were imported, most from other EU countries, but one each from the United States, Israel and Egypt.

There was a significant difference in the proportion of Clostridioides difficile-positive samples between visibly clean potatoes versus those moderately or excessively covered with soil, with the latter the most contaminated.

High potato contamination rates could have potential public health relevance, said researchers. They added very large sample sizes will be needed to understand the extent and relevance of Clostridioides difficile in foods.

Potatoes are typically washed, peeled and cooked before eating, which reduces the risk they could be a direct source of infection. However, they can serve as a vector for introducing Clostridioides difficile spores into the household environment and/or food chain, where they could persist.

Prevalent PCR ribotypes detected in the study overlap with Clostridioides difficile types found in humans, animals and soil.

“Potatoes could serve as a carrier of spore spread between countries and in the contamination of domestic environments. Such constant exposures combined with temporarily disturbed gut microbiota (impaired colonization resistance) may then contribute to the onset of community associated CDI,” said researchers.

Spread in humans and pigs
Other research, presented at the European Congress of Clinical Microbiology and Infectious Diseases (ECCMID) annual meeting in Lisbon, provided evidence for transmission of Clostridioides difficile between animals and humans.

“Our finding of multiple and shared resistance genes indicate that Clostridioides difficile is a reservoir of antimicrobial resistance genes that can be exchanged between animals and humans. The overuse of antibiotics in human medicine and as cheap production tools on farms is undoing our ability to cure bacterial infections,” said Semeh Bejaoui.

Bejaoui and colleagues from the University of Copenhagen and Statens Serum Institut investigated samples of Clostridioides difficile in 14 pig farms in Denmark and clinical isolates from hospital patients.

Genome sequencing compared isolates from pig samples to those collected from patients with Clostridioides difficile infection in 2020 and 2021. Out of 514 pig samples, 54 showed evidence of Clostridioides difficile. Thirteen sequence types found in animals matched those in patient’s stool samples.

Authors noted several limitations of the as yet unpublished work including direction of the transmission being unclear.

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