Infection caused by is of greatest concern to pregnant women and those with compromised immune systems.

Listeria

Explanation:

Listeria causes invasive syndromes such as meningitis, sepsis, and stillbirth in pregnant or immunosuppressed people. It is an intracellular pathogen and affects the persons with deficient cell-mediated immunity. Bacteria from this genus are part of the normal gastrointestinal microbiota in healthy individuals. However, in immunosuppressed individuals, the bacterium uses proteins such as internalin and phospholipase C for invasion, intracellular multiplication, and cell-to-cell spread.

Pregnant women are at the increased risk of infection due to both systemic and local immunological changes that mostly occur during pregnancy. For example, local immunosuppression at the maternal-fetal interface of the placenta may support the intrauterine infection.