Lecture 1: Part 1 Flashcards
Bacteria, most common shapes
Rod and cocci
Planes of division
of cocci:
1 plane = dipplococco
- Stay together = pair
- Long chain = streptococci
2 planes = tetrads (4 cells)
3 planes = cubical (8cells)
Random planes = staphtloccucs
Prokaryotic cell
Cell walls
Capsule
Ribosomes
Fimbrea
Plasma membrane
Nucleoid
Flagelle
Inclusions
Cell wall
Cell shape and osmotic stress protection
Capsule
Thick polysaccharide layer outside cell wall
Osmotic stress and host immune protection
Ribosomes
RNA to proteins
Fimbrea
attachement to surfaces
Pili
Plasma membrane
Permeable barrier
Location of metabolic processes
Nucleoid
Localisation of DNA
Flagelle
Cellular movement
Inclusions
Storage of C and P and other substances
Cell wall:
- Location
- Functions
Ourside plasma membrane
Aids in determining cell shape
Protection osmotic
Protect from toxins
Contributes to pthogenesis for some bacteria
Gram + and - bacteria
Gram +:
- 1 membrane
- 1 giant peptigoglycan layer
- 1 small periplasm
Gram -:
- 2 membres
- Thick peiplasm
- 1 thin peptigoglycan layer
What is associated with petigoglycane and what is the role of this structure
- Teichoic acid
- Made of glycerol-phosphate
- Assist with cell wall rigidity
Periplasm space
- Hydrolytic enzymes and proteins for nutrient processing and uptake
peptidoglycane structure
2 sugar derivatives (NAG and NAM)
NAM is linked to L-alanine, glutamic acid, DAP (-) and L-lysine (+) and D-alanine
To create a meshlike polymer, peptidoglycane can be cross linked. How does this occur?
1) Gram -:Direct cross-linking between subunits: D-Ala to DAP
2) Gram +: Cross-linking via peptide interbridges: (D-Ala to L-Lys glycine tetrapeptide)
The cross-linking in bacteria result in:
A hightly dense interconnected peptidoglycan network
Can vary between different bac species (another way to identify bacteria!)
What is on the surface of gram - bacteria
LPS
on external membrane of gram neg bacteria
What is LPS:
- made of (a.a)
- Parts
- Roles
Core polysaccaccharrides: Abe, Tha, Gal, Man, FlcN, Hep, KDD
O antigen: Diversity amoung AND within species, O antigen structure can be altered to evade host immune response
Lipid A: SIMILAR in all gram neg bacteria. endotoxin. highly hydrophobic
Adhesion, permeability, evasion of immunity
Pili
- Another name
- WHat is it
- Function
Fimbrea
- Thin proteinous fibres on surface of bacterial cells
- Hollowed-cored appendages
- Adherence to surfaces as host epithelial cell, bacteria or innate surfaces
- Type 4: twitching motility
- Conjugaison
The Capsule
- What is it
- WHere is it found
- Functions
- Polysaccharide layer that coats cell wall exterior
- gram - and +
- Host phagacytosis protection
- Protects agains dehydration
- Exclude virus or other hydrophobic toxins
- Facilitate adhesion
Koch’s Postulates
1) The microorganism must be present on every case of the disease but absent from healthy organism
2) The suspect microorganisms must be isolated and grown in a PURE CULTURE
3) The same disease must result when isolated microorganism is innoculated into a health host
4) The same microorganism must be isolated again from the diseased host
Limitations of Kochs postulates
- Asymptomatic carries
- Pure culture difficult in lab
- Ethics humans and animals (some human diseases do not cause disease in animals)
THe infectious process
Entry into host
Perisistence (adhesion, invasion, persistence)
Evasion of host defense
Replication
Damage to host
Dissemination
Maintain a reservoir (place where bacteria usually lives)
Invasion of bacteria into host cell
Attachement of bacteria to host cell
multiple mechanism of bacterial invasion
Adhesion and invasion arent always coupled
2 examples of bacterial invasaion of host cell
1) direct interaction with host receptors
- Certain bacteria may express proteins on surface that bind to host cell receptor and intiates actin-dependant phagocytocis
2) Translocation of bacterial proteins
- Certain bacteria may inject effector proteins vis SECRETION SYSTEMS into host cell, triggering actin dependant engolfment
Pathogen
a disease causing organism
Pathogenecity
The ability of an organism to cause disease
Virulence
Refers to the degree or measure of pathogenecity
Virulence factor
Bacterial products that contributes to virulence
THe most common types of virulence factors involve those that contribute to bacterial
- adherence
- Invasiveness
- Immunoevasion
- Toxigenicity
Koch’s postulates - Molecular perspective
1) The virulence trait under study should be associated much more with pathogenic strains of the species than with nonpathogenic strains
2) Inactivation of gene coding for this virulence trait (mutated) should in fact cause the bacteria to loose pathogenicity
3) Replacement of the mutated gene with the normal WT gene should fully restore pathogenicity
4) THe gene should be expressed at some point during the disease process
5) ANtibodies or immune system cells directed against the gene products should PROTECT the host
Where can virulence genes be coded?
- Extrachromosomal plasmids
- Pathogenicity island: Large clusters of DNA present within the bacterial chromosome
- Bacteriophages or transposons can intergrate genes into bacteria chromosomes
Horizontal transfer types
Transformation: F for Free DNA
Transduction: Bacteriophage injects
Conjugation: extrachromosomal plasmid
Some characteristic features of pathogenicity islands
- Insertion elements at the 5’-3’ ends suggests promiscuity as mobile elements
- Express factors that promote mobility - Intergrases, transposases
- The GC content of PAIs may differ from the remainder of the bacterial genome
- Consists of several open-reading frames - genes that encorde virulence factors
- A pathogen may have one or more PAIs
- May be found in both gram - and gram + bacteria
Example of a simplified pathogenic mechanism of Enteropathogenic E.coli
Tyoe III secretion system translocates virulence protein Tir into the host cell
Adhesion:
- Intimin of bacterial cell surface binds Tir that is displayed on host cell surface
Phosphorylation of Tyr promotes signal transduction that causes actin cytoskepeton rearrangement and pedestal formation that pushes the bacteria upwards
