A high fat diet could increase the risk of infection with Listeria monocytogenes, according to researchers from University College Cork.

APC Microbiome Ireland scientists based at the university found a high fat “western” diet reduces efficiency of the immune system to fight infectious disease in the gut.

Researchers discovered that feeding mice with such a diet, which is high in fat and low in fermentable fiber, affected the immune system and bacteria in the gut, also known as gut microbiota.

Even short-term consumption of the high fat diet increased the number of goblet cells in the gut, which are the target for infection by Listeria, as well as causing changes to microbiota composition and the immune system.

Findings published in the journal Microbiome suggest diet should be a consideration when developing models that reflect human infectious disease and it should be a factor in future evaluation of the infectious dose of the pathogen.

Vanessa Las Heras, a PhD student, did the study at the Science Foundation Ireland Research Centre.

“Short-term consumption of the high fat diet increased levels of Firmicutes bacteria in the gut which are associated with obesity. The effects of diet were also seen beyond the gut, with reduced levels of immunity throughout the body, local alterations to gastrointestinal cell function and changes to the gut microbiota that enhanced the progression of Listeria infection,” she said.

Research was funded through EU Horizon 2020 and by Science Foundation Ireland through a grant to APC Microbiome Ireland.

Scientists examined microbiota and host physiological changes influenced by diet immediately prior to infection and during peak period of active infection.

For two weeks, mice were fed a high fat diet with 45 percent of total caloric intake from fat; a matched low-fat diet with 10 percent of total caloric intake from fat; or regular chow with 18 percent of total caloric intake from fats.

At day 13, mice were infected with a strain of Listeria monocytogenes in which a protein was altered to increase the efficacy of the model as a measure of invasive disease and infection was determined 72 hours later on day 16 of the study. Animals were euthanized and the number of Listeria monocytogenes colony forming units (CFU) per organ was determined by plating homogenized organs.

A 200 microliter inoculum of 3.2 × 109 CFU for the oral inoculation infection and 9 × 104 for intraperitoneal infection was used. Intraperitoneal means within the peritoneal cavity — the area that contains abdominal organs.

“Our results suggest that diet may be a significant influencer of resistance to infectious disease through effects on the gut microbiota and immune system. This has important implications for human health, especially during pregnancy, in old age and in immunocompromised individuals,” said Dr. Cormac Gahan, leader of the study.