Sunday 30 November 2003
Miniepidemics of L. monocytogenes have been linked to dairy products, chicken, and hot dogs. Pregnant women, their neonates, the elderly, and immunosuppressed persons (e.g., transplant recipients or AIDS patients) are particularly susceptible to severe L. monocytogenes infection.
In neonates, L. monocytogenes may cause disseminated disease (granulomatosis infantiseptica) and an exudative meningitis, both of which are also seen in immunosuppressed adults.
L. monocytogenes has leucine-rich proteins on its surface called internalins, which bind to E-cadherin on host epithelial cells and induce internalization of the bacterium.
In the host cell cytoplasm, ACTA, a bacterial surface protein, binds to host cell cytoskeletal proteins and induces actin polymerization, which propels the bacteria into adjacent, uninfected host cells.
Resting macrophages, which internalize L. monocytogenes through C3 activated on the bacterial surface, fail to kill the bacteria. In contrast, macrophages that are activated by IFN-γ phagocytose and kill the bacteria.
Hence, unlike most other Gram-positive bacteria, protection against L. monocytogenes is mediated largely by IFN-γ produced by NK cells and T cells.
Listeria monocytogenes infection
< object width="425" height="350"> < param name="movie" value="http://www.youtube.com/v/N3NJO1VWw-A"> < /param> < param name="wmode" value="transparent"> < /param> < embed src="http://www.youtube.com/v/N3NJO1VWw-A" type="application/x-shockwave-flash" wmode="transparent" width="425" height="350"> < /embed> < /object>