Symbionts and Pathogens Flashcards
1
Q
Symbionts colonisation of Animals
- What each partner called
- Healthy animal characteristics
A
- Host & microbes exist over long period of time in dynamic co-operation
- larger partner = host
- smaller partner = symbiont
- in healthy animal; internal tissues normally free of microorganisms (i.e. brain, muscle)
- body surface colonised by complex community of microorganisms
2
Q
Types of Symbiosis (3)
A
- Commensalism: Symbiont benefits, no harm/benefit to host
- Mutualism: both host & symbiont benefit - obligatory relationship
- Parasitism: Symbionts benefit at expense of host
3
Q
Benefits of symbiosis w/ bacteria
A
- Benefits may involve nutrient exchange b/w animal and bact. symbiont
- animals cannot syn. some a.a. & vitamins
- break down some complex molecules
- bacterial partner may add value by doing some of these things
- together both partners have advantages over single species
4
Q
Bacteria in large intestine
-16S rRNA
A
- More than 800 bact species est. to inhabit colon - most anaerobic
- majority can’t be cultured by traditional methods
- done by extracting DNA and looking at 16S rRNA sequence variation
- is a component of prokaryote ribosomes
- is a highly conserved gene
5
Q
Coevolution w/ microbiota
A
- Microbes often only thought of as cause of disease - actually contribute large amount to human genome
- contributes approx 8 million unique protein coding genes
(i. e. there are lots of microbes w/in us)
- contributes approx 8 million unique protein coding genes
6
Q
Infectious Diseases
-What it results from
A
- Is the change from the state of health due to the presence of an organism of its products
- results from:
- disturbance in the balance b/w bacterial virulence and host resistance
*primary goal of microorganism is to acquire nutrients and multiply, rather than to harm the host
7
Q
Bacterial action upon exposure to cell
- How cell responds
- Ways bacteria can protect themselves from host immune system
A
- First attach to cell surface & set up a population of organisms
- Cells respond by activating innate immune response
- pathogenic bacteria then invade superficial layer
- virulent bacterial may be protected from death by number of survival factors;
- polysaccharide capsule
- secretion of molecules that specifically inhibit the innate host response
8
Q
3 Factors that determine pathogenicity of an organism
A
- Invasiveness or invading host tissues
- Infectivity or evading host defences
- Virulence or toxigenicity (actively damaging host cells or processes)
9
Q
Number of invading microbes
- LD50
- ID50
A
-Virulence of a microbe or potency of its toxin is epressed as the LD50
LD50 (Lethal dose for 50% of hosts) is no. of microbes in a dose that will kill 50% of inoculated test animals
ID50 (Infectious dose for 50% of hosts): is dose required to produce a demonstrable infection in 50% of test animals
10
Q
Virulence of the pathogen
- what virulence is directly related to
- 4 Variables that affect virulence
A
- Degree of virulence related directly to the ability of the organism to cause disease despite host resistance mechanisms
- Affected by;
1. Number of infecting bacteria
2. Route of entry into the body
3. Specific and nonspecific host defense mechanisms
4. Virulence factors of the bacterium (produced by a microorganism and cause disease)
*no. of bacteria required to cause disease changes - depends on the species
11
Q
Overview of process of infection by pathogen (6 steps)
A
- Enter the host
- Adhere to cell surfaces
- Colonise cell surfaces
- Invade tissues
- Evade host defenses
- Produce toxins and other harmful products
12
Q
Innate immunity (of host)
- What it is
- Features of it
A
- Is first line of defence by a mammalian host during period after initial exposure
- If invader eludes the first, non-specific line of defence, then specific immune system is triggered
- is dependent on macrophages and dendritic cells (DCs)
- these cells can sense pathogens & respond promptly by producing a variety of cytokines (cellular messengers that enhance response)
- is non-specific
- is no memory of lasting protective immunity
- majority of microorganisms destroyed w/in minutes or hours by innate defenses
13
Q
Pathogen-Associated molecular patterns (PAMPs)
- what it is (characteristics of RAMPs)
- Importance in innate immune system
A
- Pathogens, esp. bacteria, have molecular structures that;
- are not shared w/ hosts
- shared by many related pathogens
- relatively invariant (i.e. don’t evolve rapidly)
- they are what our innate immune system recognizes
14
Q
5 examples of PAMPs (pathogen-associated molecular patterns)
A
- Flagellin protein of bacterial flagella
- Peptidoglycan layer of gram-pos. bacteria
- Lipopolysaccharide of gram-neg. bacteria
- Double stranded RNA
- Unmethylated DNA (DNA bases in eukaryotes have methyl groups attached)
15
Q
Toll - like receptors
- what it is
- where they are found
- what do they promote
A
- Macrophages, dendritic cells & epithelial cells have set of receptors that recognize different types of RAMPs
- Toll-like receptors = transmembrane proteins involved in detection of microbes upon infection
- activation promotes the production of pro-inflammatory cytokines and molecules of the innate immune system
