Abstract
Listeria monocytogenes is an intracellular pathogen responsible for listeriosis, a foodborne disease that can lead to life-threatening meningitis. The 2011 L. monocytogenes cantaloupe outbreak was among the deadliest foodborne outbreaks in the United States. We conducted in vitro and in vivo infection analyses to determine whether strains LS741 and LS743, two clinical isolates from the cantaloupe outbreak, differ significantly from the common laboratory strain 10403S. We showed that LS741 and LS743 exhibited increased virulence, characterized by higher colonization of the brain and other organs in mice. Assessment of cellular immune responses to known CD8+ T cell antigens was comparable between all strains. However, pre-existing immunity to 10403S did not confer protection in the brain against challenge with LS741. These studies provide insights into the pathogenesis of clinical isolates linked to the 2011 cantaloupe outbreak and also indicate that currently utilized laboratory strains are imperfect models for studying L. monocytogenes pathogenesis.
Highlights
Listeria monocytogenes is an intracellular pathogen responsible for listeriosis, a foodborne disease that can lead to life-threatening meningitis
We confirmed that similar growth rates between L. monocytogenes strains 10403S, LS741 and LS743 were observed when bacteria were grown in Brain Heart Infusion (BHI) broth over 25 hours (Fig. 1a)
We did not observe any differences in the intracellular replication rate between both outbreak strains and 10403S (Fig. 1d). These data indicated an increased ability of the L. monocytogenes outbreak strains LS741 and LS743 to invade host cells and spread cell-to-cell compared to 10403S, yet the intracellular replication rate was similar among all strains
Summary
Listeria monocytogenes is an intracellular pathogen responsible for listeriosis, a foodborne disease that can lead to life-threatening meningitis. We first infected BALB/c mice intravenously with 1–2 × 104 CFU of L. monocytogenes strains 10403S, LS741, or LS743 and the number of bacteria present in the spleen, liver and brain of each mouse was determined 72 hours post-infection.
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