Lecture 2: Bacterial Pathogenesis Flashcards
(38 cards)
Pathogen
- Microorganism capable of producing pathology (disease) in a percentage of normal, healthy non-immune individuals
- if administered in sufficient dose, will almost always cause disease, but at lower doses infection may result without overt disease (sub-clinical infection)
What is the goal of a pathogen?
- to reproduce, not cause disease per se
- disease of host is often associated with the propagation of the microorganism and/or its spread
- Ex: cough facilitates transmission
Opportunistic pathogen
-don’t cause disease in a healthy host, but will cause disease only in individuals whose normal defense mechanisms have been compromised
Extracellular pathogen vs. Intracellular pathogen
- E: bacteria or parasites that replicate outside of host cells
- I: bacteria or parasites that replicate inside of host cells
-will determine the type of immune defenses it encounters
Obligate pathogens
-cannot be found anywhere but in association with their host
Obligate intracellular pathogens
- can grow only inside of host cells, and cannot be cultured extracellularly
- all viruses
Facultative pathogens
-can grow or survive in the environment as well as in their host
Facultative intracellular pathogens
-can grow inside and outside of cells and can be cultured extracellularly on agar plate in lab
Virulence
-refers to the degree of disease that a pathogen can cause
T/F: the most successful pathogens are the more virulent
-False: often not the case because it doesn’t pay to kill off your host before you’ve had a chance to successfully reach new host
Virulence factors
- components of pathogen that contribute to its ability to cause an infection
- toxins, adhesions, iron acquisition, special adaptations of metabolism
Bacterial infections can be _____, _______, or _______.
-acute, chronic, or latent
3 main ways in which bacteria breach the body’s barriers and cause disease
- intracellular growth of bacteria
- disruption of host cell function from outside (extracellular pathogens)
- extracellular secreted toxins that kill or alter host cells
To be successful, all pathogens have to be able to do what 3 things?
- gain entry
- establish niche and replicate
- reach new host
Routes of bacterial entry/transmission
- ingest
- breathe in
- sexual contact
- vector (flea, tick bite)
- wound
- mother to fetus
Why might bacteria prefer to grow inside cells? (intracellular bacterial pathogens)
- access to nutrients
- avoid extracellular immune defenses
- cross barriers and reach deeper tissues
How and where does listeria enter a cell?
-Tips of intestinal villi because this is where E-Cadheren Receptor is transiently expressed (receptor-mediated entry)
How does listeria spread within the body?
- inside a cell, it polymerizes host actin at 1 end using a polarized bacterial surface protein (ActA)
- results in pseudopods that spread to adjacent cells
- Cytotoxic T cells are key to resolution
2 ways for bacteria to enter non-phagocytic cells:
- Zipper: receptor mediated
- Trigger
Ways in which extracellular bacteria can cause pathology
- secrete toxins
- damage cells of mucousal surface
- induce inflammation which can damage host cells
Mechanism of EPEC infection
- creates loose association with intestinal epithelial cells via BFP
- Then using type 3 secretion system (TTSS) injects Tir into bacterial cells
- Bacterial intimin makes tight association with Tir, now on epithelial membrane to form tight connection
- Additional effectors are injected that interact with host cytoskeleton and created attaching and effacing lesions
- Translocated effectors also disrupt tight junctions
Why is the end result of EPEC infection diarrhea?
-tight junction disruption causes disruption in sodium gradient and a flow of water into the intestinal lumen
EPEC functions are encoded on ________.
-Pathogenicity islands on EPEC chromosome
IgA protease
- method bacteria can use to not be phagocytosed
- cleave IgA between Fab and Fc so it cannot react with FcR on phagocytes
