Listeria hysteria! Outbreaks have been popping up in a variety of foods over the years—however, not all infections are created equal. The severity of L. monocytogenes infection, also known as Listeriosis, is dependent on both the host’s immune system and the virulence of the strain.Immunocompromised populations may experience encephalitis, meningitis, bacteremia, miscarriage, gastroenteritis, or even death. Immune-competent individuals may experience mild to no symptoms.0.5–5% of humans even carry low levels L. monocytogenes in the gastrointestinal tract with no symptoms.

Listeria is acquired through ingestion of contaminated foods. The most common culprit is ready to eat (RTE) foods such as deli meats, cheeses, and ice cream. The gut microbiome serves as a form of defense by activating the host’s immune system, production of bacteriocins, and depletion of nutrients.Pregnancy, chemotherapy, and other conditions causing immunodeficiency can affect both the immune system and composition of gut microflora.

Simone Becattini and Eric G. Pamer’s research group simulated this affect by disrupting the microbiome of healthy and immunocompromised laboratory mice through antibiotic treatments. These treatments made them more susceptible to L. monocytogenes infection and subsequent colonization and dissemination.  A different group of mice treated with cyclophosphamide, doxorubicin, and chemotherapy drugs were more susceptible to L. monocytogenes infection. Once treated with additional antibiotics, the mice were even more likely to be infected. If the mice survived after colonization, L. monocytogenes remained in their intestinal tract for up to 3 weeks allowing the possibility for relapse

The researchers found four different species of Clostridia bacteria in the gut microbiome that, when present, were able to limit L. monocytogenes infection. Transfers of these bacteria into germ-free mice limited Listeria colonization and dissemination because the Clostridia outcompeted the Listeria. Transfers of intestinal bacteria, also known as Fecal Microbiota Transplants (FMTs), are used to treat various conditions including Irritable Bowel Syndrome (IBS) and Clostridium difficile infections.

This study revealed a new potential avenue of Listeria protection and treatment. FMTs could help reduce the instances of Listeriosis and the subsequent deaths associated with these infections. For example, pregnant women in their third trimester show reduced numbers of Clostridia species and are at high risk of infection. FMT treatments could be a safe and helpful way to reduce instances of Listeriosis and save lives for those that are at most risk.

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