Outline:

• Invasiono Penetrating barriers

• Avoiding the Host Defenseso Hiding within a host cello Avoiding killing by CSPo Avoiding destruction by phagocyteso Avoiding antibodies

Invasion: Breaching Anatomical Barriers

• Find new niche with few competitors• Gain access to rich nutrient supply• 1. Skin: tough barrier, rely on skin-damaging

injuries (wounds, cuts) (Staphylococcus aureus) • 2. Crossing mucous membrane (e.g.

intestinal epithelial cells) (Most pathogens)

Ruffling method of invasion

Shigella and Listeria species

Avoiding the Host Defenses1. Hiding within host cells• Cell-to-cell Spreading

Avoiding the Host Defenses• 2. Avoiding complement killing

– Gram- bacteria are susceptible to MAC because their outer membrane serves as a target.

– Serum resistant bacteria– The same mechanism as the host cells use

Avoiding the Host Defenses

• Avoiding destruction by phagocytes

• Avoiding Antibodies

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Avoiding the Host Defenses