Introduction to Bacteria Flashcards
List the different groups of microorganism in microbiology
Fungi
Parasites
Bacteria
Viruses
Prions
Define mycology
The study of fungi
This consists of yeast & mould
Define parasitology
The study of parasites
This includes protozoa and higher multicellular organisms such as worms, fleas & flies
Define bacteriology
The study of bacteria
This includes:
* Gram negative (Gram -Ve)
* Gram positive (Gram +Ve)
* Acid fast (Mycobacteria these group with Gram +ve)
* Mycoplasma (No cell wall)
Define virology
The study of viruses
Define what unconventional agents of microorganisms are
Single proteins known as prions (studied in NMSK)
List the basic structural components of bacteria
Genome - chromosome & plasmid
Cell wall
Cell membrane
Capsule
Flagella
Pilus
Ribosomes
Granules
mRNA
What is the bacteria genome (choromosome)?
Haploid circular DNA
It is longer than the typical prokaryotes and so must be compacted by supercoiling
It requires DNA gyrase which is unique to bacteria
formation of histone-like proteins further packages DNA
DNA-protein complex called the nucleoid.
Carries essential core genes of the bacteria.
Carries other genes that define the properties of the bacteria.
What is the bacteria genome (plasmid)?
Not all bacteria have plasmids
It is an independent small DNA molecules
Has partition genes so when bacteria divide both cells gain plasmid.
Plasmids can transfer between related bacteria.
Plasmids can carry genes for a range of properties – virulence genes, antibiotic resistance gene
What is the structure and function of a bacteria cell wall?
Provides structure & form -protects from osmotic lysis
Rod/bacillus, coccus, vibrio/spiral -shape doesn’t always help identify the bacteria
Made of peptidoglycan which are chains of polysaccharides cross linked with poly-peptides, and this determines morphological shape of the bacteria
Most have cell walls
Those without are mycoplasmas
Shape is not determined
What is the bacterial membrane?
Barrier -but affected by diffusion and osmotic effects
Passive transport
Osmotic diffusion in most cases there is a slight positive osmotic pressure on the
bacterial membrane.
Simple diffusion of lipid-soluble & very small molecules.
Facilitated diffusion of normally non-diffusing compounds by a trans-membrane
protein.
Active Transport
A gradient of one molecule is used to power the Co-transport of other molecules.
Active transport to actively take up material normally at expense of ATP.
What are flagella?
Multi-component protein tails.
The filament is made of many flagellin subunits.
Powered by proton motive gradient across membrane.
Different bacteria can have different patterns of flagella.
Not all bacteria have flagella.
Essential virulence component for a number of pathogens.
What is the bacterial capsule?
Extracellular polymeric material secreted around the bacteria and loosely associated with its surface.
Hard to visualise (often easier to see where it excludes a background stain).
Most are capsules polysaccharides (some exceptions Bacillus anthracis has a poly-peptide capsule- has a specific stain anthrax)
What is the function of the bacterial capsule?
Protection against desiccation (drying).
May facilitate adherence to surfaces.
May provide a matrix for biofilms of bacteria.
Some interfere with phagocytosis
What are pili/fimbriae?
Two names mean the same
Strands of protein attached to bacteria surface.
Made of pilin peptide subunits.
What is the function of pili/fimbriae?
Adhesion- Some are virulence factors.
Some bind to sugars on host cells to aid attachment Some involved in biofilm formation
Plasmid transfer
Some plasmids encode for sex-pili (F-pili), which are involved in conjugation
(connection of one bacterium to another) mobilization of DNA between bacteria
Describe the structure in Gram negative bacteria
Outer membrane contains porins
-charge & size gates
-AKA Outer membrane proteins
Some antibiotics wont be able to penetrate this
The wall is complex structure
Because of this doesnt stain very well and appears pink
Describe the structural of Gram positive bacteria
Thick uniform cell wall composed of peptidoglycan and teichoic acids
During staining the peptidoglycans are dehydrated when alcohol added making it more permeable to the counter stains and so they appear purple
Outline the acid fast property in mycobacteria
Similar structure to Gram positive bacteria
Will stain Gram positive but they also have an acid-fast property for stains.
Contain a large number of glycolipids, especially mycolic acid in their cell wall.
Waxy- Impacts on how stains are taken up and held. Acid-fast bacteria resist decolourization acid-alcohol (i.e. Acid Fast).
Acid Fast staining is used to identify acid-fast bacteria such as Mycobacteria but also stain a few other bacteria like Nocardia sp
What is the Ziehl Neelsen modified acid fast stain?
Stain with Ziehl-Neelsen carbol fuchsin
De-stain with an acid alcohol Counter stain with methylene blue
Those that maintain the red colour are defined as acid fast. Can be used on smears or tissue sections
What is the Ziehl Neelsen modified acid fast stain method?
Stain with Ziehl-Neelsen carbol fuchsin
De-stain with an acid alcohol Counter stain with methylene blue
Those that maintain the red colour are defined as acid fast. Can be used on smears or tissue sections
Outline the steps of gram staining
Add primary stain (crystal violet)
Add mordent (iodine)
Forms a complex with dye & bacteria
Add alcohol (ethanol) this dehydrates peptidoglycan making them more permeable
add counter stain
What are endospores?
Dormant highly resistant bodies produced by some bacteria
What are bacterial endospores?
Restricted to a few Gram-positive genera.
Under specific conditions the bacteria form dormant highly resistant bodies These can survive adverse conditions.
One bacterium will form one endospore. A spore is a layered dehydrated structure, metabolically inert, contains high levels of small acid soluble proteins
Dipicolonic acid present not found in vegetative bacteria cells accumulates along with high levels of calcium.
Outline the germination stages of endospores
Activation.
In lab heat shock. In environment simple ageing leads to activation.
Germination
Including rehydration excretion of calcium and dipicolonic acid.
Growth and shedding of remaining spore coat.
New vegetative cell will start growing
What type of bacteria are Mycoplasmas?
Mycoplasmas group by phylogenetic analysis with the Gram +ve bacteria.
We refer to them as Mycoplasmas or their genus/species name during the course
Mycoplasmas lack the cell wall, so they do not stain as Gram +Ve
They have reduced genomes - limited number of essential components and ‘pinch’ other metabolites from their host environment
Having no cell wall means what?
They have not distinct structural morphology so appear pleomorphic.
They are fragile.
They live closely associated with their hosts cells relying on the homeostatic mechanisms of the host to maintain their environment.
Describe clinical relevance of common structural differences between bacteria.
Gram negative bacteria has lower sensitivity to the antibiotics containing B lactam than gram positive due to outer membrane composition
CR: Although some new antibiotics can penetrate, it worth considering different antibiotics to treat whilst also taking into account stewardship
Gram negative contain may more pili making the bacteria more virulent
Gram negative have a higher lip content which can slow entry for some antibiotics
CR: consider when choosing antibiotic
LPS present in cell mebrane of gram negative
CR: releases endotoxins when lysed which stimulate host immune response
Some Gram postive Bacilli form pores
CR: Disinfection procedures as well as antibiotic choice
