Pathogenesis Pt. 1: Adhesion, Colonization & Invasion

infection

persistence of an organism in or on a host

infectious disease

colonization or invasion of the host resulting in tissue damage

virulence factors

any component of a microorganism that contributes to

• invasion, evasion of host defenses, tissue damage 

primary pathogen

a microorganism that causes disease even in healthy host

opportunistic pathogen

a microorganism that normally causes disease only in host that are compromised in some way

what are the steps that lead to infectious diseases

1. adherence 

2. replication

3. invasion 

4. evasion of host defenses 

5. tissue damage 

adhesins

microbial surface structures that attach to a host cell receptor

integrins

host cell receptors that bind to microbial adhesins

what are pili

fimbriae that are hair like projections that are present on the surface of bacteria 

where is pili mostly found on

gram negative bacteria

what does pili facilitate

adherence of uropathogens to the mucosal surface of the bladder

what are special types of pili used for

motility in Neisseria gonorrhoeae and Pseudomonas aeruginosa.

non-pili adhesins

Adhesins of Gram positive bacteria

bacterial capsules

An extracellular polysaccharide matrix

what do bacterial capsules provide

1) promotes adherence to host cells

2) aids in adherence to other bacteria (biofilms)

3) prevents phagocytosis

what are integrins

host cell receptors

what are integrins comprised of

glycolipids and glycoproteins

what are integrins important for

host cell function

what do integrins determine

host and tissue tropism

host tropism

the susceptibility of a host to be infected by a microorganism

tissue tropism

the cells or tissues of a host that support the growth of a particular microorganism 

what do microbes have to do typically

replicate to cause disease

sites of replication within a host

extracellular and intracellular growth

extracellular growth

outside of host cells

intracellular growth

growth inside of a host cell

what are some bacterial pathogens

facultative intracellular pathogens

facultative intracellular pathogens

can grow on either mucosal surfaces or within host cells

Strategy for survival and replication for bacteria/ pathogens 

1. Evasion of host defenses

2. Source of nutrients

3. Less competition

4. Access to host cell machinery (replication of viruses 

what do some pathogens exploit

host internalization mechanisms

examples of how pathogens exploit host internalization mechanisms

• phagocytosis by innate immune cells (neutrophils, dendritic cells and macrophages)

• forced uptake into nonphagocytic cells 

what must microorganisms that damage host cells do

escape and invade a new host cell

how can viruses leave the host cell

bud from a host cell, or escape via lysis of the host cell.

how do some bacteria/ pathogens escape the cell

some bacteria exploit host cell proteins to propel themselves into adjacent healthy host cells 

host-microbe interactions 

1. removal/ destruction by host defenses 

2. colonization without disease 

3. replication and tissue damage 

what are host defense factors 

1. immune status (immunocompromised)

2. co-evolution of host and pathogens 

pathogens routes of entry

ingestion, inhalation, trauma, needle stick, arthropod bite, sexual transmission

pathogenicity

The ability or potential for an organism to cause disease

virulence

The degree or intensity of an organism’s pathogenicity

What are the benefits for bacteria that live within host cells (intracellular pathogens)?

receiving protection from the immune system,

gaining access to a rich source of nutrients,

evading competition from other microbes