This episode explores Listeria monocytogenes and related aerobic, non–spore-forming Gram-positive bacilli. Drawing from Murray’s chapter, the focus is on Listeria’s distinctive ability to survive and replicate within host cells.

The narrative centres on its pathogenesis: ingestion via contaminated food, intestinal invasion, survival within macrophages, escape from the phagolysosome via listeriolysin O, and actin-based intracellular motility that allows cell-to-cell spread without extracellular exposure. This strategy explains its predilection for vulnerable populations - neonates, pregnant individuals, the elderly, and the immunocompromised.

Clinical patterns include meningitis, sepsis, and transplacental infection. The episode reinforces the principle that intracellular pathogens demand cell-mediated immune responses, linking back to earlier immunology chapters.

Other related Gram-positive rods are acknowledged, but Listeria remains the central teaching organism - subtle, adaptable, and capable of breaching both intestinal and placental barriers.

Key Takeaways

* Listeria monocytogenes is a Gram-positive intracellular bacillus

* Infection often follows ingestion of contaminated food

* Listeriolysin O enables escape from phagosomes

* Actin-based motility permits cell-to-cell spread

* Vulnerable populations are at highest risk for invasive disease

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