Lecture 2. Host-Parasite Interaction

Pathogen

Disease causing agent

Commensalism

Microorganism benefits while host is not harmed

Mutualism

Microorganism and host benefit

Parasitism

Microorganism benefits while the host is harmed

Indigenous (normal) biota

Microorganisms commonly found on or in healthy persons

Resident biota

Microorganisms that colonize an area for months or years

Transient biota

Microorganisms temporarily colonizing a host

Carrier state

Condition of hosts capable of transmitting the infection

Opportunists

Normal flora causing disease when the habitat is altered, or the host is immunocompromised

Virulence

Mechanisms that allow infectious organisms to persist in a host & cause disease

Highly virulent

Pathogens cause severe, potentially fatal disease with only a small number of organisms

Low virulence

Organisms that either cause mild disease, require a large number of organisms to establish infection

Avirulent

Do not cause disease at all

Polysaccharide capsules

Inhibit phagocytosis

Protein A is located in:

The bacterial cell wall of Staphylococcus aureus

Protein A interferes with

The binding of the host’s antibodies to the surface of the organism

Exotoxins

Harmful proteins produced & released by bacteria into their surroundings

Endotoxins

Harmful substances found in the outer membrane of Gram-negative bacteria