Bacteria Flashcards
Meaning: opportunistic pathogen
A pathogen that currently lives in body’s flora but transits to further places to cause disease.
Meaning: pathogenicity
The ability to cause a disease.
Virulence
The degree/intensity of pathogenicity defined by invasiveness, infect ivory and pathogenic potential.
Virulence factor
Biological product that contributes to virulence or pathogenicity
Pathogenesis
Strategy, mechanism of process by which disease develops
Primary pathogen
Directly caused disease
Latent disease
Periods of inactivity alternate with obvious symptoms, low severity
Acute disease
High severity develops and resolves rapidly.
Chronic disease
Low severity, develops slowly and persists.
Difference between Gram negative and Gram positive
Gram positive have thick peptidoglycan layer (100 layers) with lipoteichnoic and teichnoic acids in it. Molecules are able to diffuse through the peptidoglycan layer to the plasma membrane below. Original stain is more resistant to washing so it stays
Gram negative: thin peptidoglycan layer (6 layers) peri plasmid space between outer lipopolysaccharide membrane and peptidoglycan wall). Outer lipopolysaccharide membrane (non energised) with poring to allow molecules to diffuse in and out. The original stain washes off so the second stain is shown.
What are the main characteristics of a prokaryote?
- Absence of nuclear membrane or discrete nucleus
- single circular DNA chromosome
- plasmids present
- reproduce via binary fission (not mitosis)
- complex cell wall
What are the main bacterial shapes and examples of each?
Bacilli rods: E. Coli, Shigella, Clostridium.
Cocci: staphylococcus (clusters) and streptococcus (chains)
Spiral: H. Pylori
Comma-shaped: Vibrio Cholerae.
3 bacterial extra cellular structures and their functions?
- Capsule (extra cellular polysaccharides): prevents dessication (drying out), resists phagocytosis, maintains key hydrolytic enzymes close to the cell, adhesion to surfaces.
- Fimbriae/pilli: attachment (not motility).
- Flagella: motility.
What are the components of a usual bacterial genome?
-singular circular dsDNA chromosome NOT complexed with histones and plasmid DNA (extra-chromosomal DNA that can vary in size and copy number).
What are the characteristics of plasmids?
- extra chromosomal DNA
- contains non-essential genes that confer selective advantage
- exist and replicate independently of chromosomes
- usually small, closed circular DNA.
5 main factors that control the growth of bacteria
Temperature, pH, external osmolarity, oxygen, nutrient concentration.
Four distinct phases of bacterial population growth?
- lag phase: fellas adapt to new conditions, enzymes and new metabolites accumulate
- exponential phase: maximum constant growth phase
- stationary phase: slow death of cells balanced by slow multiplication due to insufficient oxygen/nutrient supply.
- death phase: sharp drop in number of viable cells.
3 broad types of nutrient media and why are they useful?
- Enrichment: allows growth of many types of bacteria.
- Selective: allows growth of selected group of bacteria only.
- Differential: allows growth of a number of types of bacteria BUT colonies develop with defined characteristics.
When is the microbiome established and what is its function?
Established in the first few months of life and effects human cell function and immune system balance.
Some examples that the microbiome in human tissue is related to?
IBD (Crohn’s), childhood asthma, allergy development, colorectal and gastric cancer, obesity, type 2 diabetes mellitus, COPD, cystic fibrosis.
What are the two major virulence factor and give examples of each?
- Products that promote capacity to establish infection (competition with endogenous micro flora) e.g. Adherence to host mucosa, scavenging of essential nutrients. Resistance to host defences e.g. Survive within the host.
- products that damage host and cause symptoms e.g. Hydrolytic enzymes, toxins, mediators of host inflammatory responses.
3 methods of DNA transfer between and among bacteria.
Transformation: plasmid of free DNA
Conjugation: direct transfer via cell-cell contact
Transduction: transfer via bacterial viruses.
Distinguish between Pathogenesis, pathogenicity and virulence.
Pathogenesis is the mechanism or process by which bacteria causes disease.
Pathogenicity is the ability of the pathogen to cause disease.
Virulence is the severity of a pathogens ability to cause disease.
What are the steps in bacterial Pathogenesis?
- Transmission: from host to reservoir.
- Colonisation: adherence and invasion of usually mucosal surfaces.
- Proliferation: within host/invasion (host provides nutrients).
- Evasion: of host immune system
- Transmission to another host/reservoir.
