Understanding the impact of pathogenic bacteria in the intestinal microbiota of pigs and chickens on human health

The micro-organisms that colonise the digestive system have proven effects on the health of their host, yet the factors modulating the microbiota remain largely unknown. ANSES took part in the RIMICIA (Review Impact MICrobiome In Assessment) project, funded by the European Food Safety Authority (EFSA). The purpose of this project was to identify the parameters that could be taken into account in order to include the microbiota in the assessment of risks to animal and human health. Scientists from the ANSES Ploufragan-Plouzané-Niort laboratory carried out the animal health research, while the Spanish National Research Council handled the human health aspect.

The scientists first explored the scientific literature to identify the factors modulating the microbiota that had already been highlighted by previous research. They found that these ranged from nutrients and chemical products to food additives and the presence of micro-organisms. They then focused on selected factors that merited further research.

Influence of Salmonella and Campylobacter on chicken microbiota

“The literature review revealed that the presence of certain micro-organisms modulates the composition of chickens’ intestinal microbiota”, explains Marianne Chemaly, head of the ANSES Hygiene and quality unit for poultry and pork products. “That’s why we focused the rest of the project on studying the impact of the presence of Campylobacter and Salmonella on chicken microbiota. These two bacteria are responsible for the main foodborne illnesses in Europe, contaminating humans during handling in the kitchen or through undercooked food. They are pathogenic for humans, but not for animals.”

After inoculating chickens with one or both bacteria at the same time, the scientists observed that the presence of Campylobacter had little influence on microbiota composition. On the other hand, the presence of Salmonella reduced the richness and diversity of the intestinal microbiota, without any observable effect on animal health.

Co-infection increases the quantity of bacteria

There is little effect on the microbiota when both bacteria are present at the same time. On the other hand, co-infection by Salmonella and Campylobacter increases the quantity of both bacteria in the intestine, compared with when each of them is alone. “As the likelihood of these bacteria contaminating meat is proportional to their quantity in animal intestines, this increases the risk to human health”, explains the scientist.

A mycotoxin associated with Salmonella slows growth in pigs

According to the scientific literature, one of the factors significantly influencing the intestinal microbiota of pigs is the presence of the mycotoxin deoxynivalenol (DON). This toxin, produced by a fungus, can contaminate animal feed. The research carried out by scientists working on the RIMICIA project was designed to supplement current data on the mycotoxin’s effect, and find out whether it stimulates the proliferation of Salmonella. They thus added DON to the pigs' feed and inoculated some of them with Salmonella. While DON had not changed the quantity of Salmonella in the pigs' intestines by the end of the experiment, those that had received both DON and Salmonella weighed less than the others, despite having consumed the same quantity of feed. The effect of DON on the intestinal microbiota differed from one individual to another; this variability needs to be explained by more detailed studies. This project explored other subjects, including a particular focus on the link between animal welfare and intestinal microbiota. The results should be published in the coming months.