Introduction to Bacteria

Question 1

List the different groups of microorganism in microbiology

Answer 1

Fungi
Parasites
Bacteria
Viruses
Prions

Question 2

Define mycology

Answer 2

The study of fungi

This consists of yeast & mould

Question 3

Define parasitology

Answer 3

The study of parasites

This includes protozoa and higher multicellular organisms such as worms, fleas & flies

Question 4

Define bacteriology

Answer 4

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)

Question 5

Define virology

Answer 5

The study of viruses

Question 6

Define what unconventional agents of microorganisms are

Answer 6

Single proteins known as prions (studied in NMSK)

Question 7

List the basic structural components of bacteria

Answer 7

Genome - chromosome & plasmid
Cell wall
Cell membrane
Capsule
Flagella
Pilus
Ribosomes
Granules
mRNA

Question 8

What is the bacteria genome (choromosome)?

Answer 8

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.

Question 9

What is the bacteria genome (plasmid)?

Answer 9

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

Question 10

What is the structure and function of a bacteria cell wall?

Answer 10

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

Question 11

What is the bacterial membrane?

Answer 11

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.

Question 12

What are flagella?

Answer 12

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.

Question 13

What is the bacterial capsule?

Answer 13

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)

Question 14

What is the function of the bacterial capsule?

Answer 14

Protection against desiccation (drying).

May facilitate adherence to surfaces.

May provide a matrix for biofilms of bacteria.

Some interfere with phagocytosis

Question 15

What are pili/fimbriae?

Answer 15

Two names mean the same

Strands of protein attached to bacteria surface.

Made of pilin peptide subunits.

Question 16

What is the function of pili/fimbriae?

Answer 16

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

Question 17

Describe the structure in Gram negative bacteria

Answer 17

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

Question 18

Describe the structural of Gram positive bacteria

Answer 18

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

Question 19

Outline the acid fast property in mycobacteria

Answer 19

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

Question 20

What is the Ziehl Neelsen modified acid fast stain?

Answer 20

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

Question 21

What is the Ziehl Neelsen modified acid fast stain method?

Answer 21

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

Question 22

Outline the steps of gram staining

Answer 22

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

Question 23

What are endospores?

Answer 23

Dormant highly resistant bodies produced by some bacteria

Question 24

What are bacterial endospores?

Answer 24

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.

Question 25

Outline the germination stages of endospores

Answer 25

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

Question 26

What type of bacteria are Mycoplasmas?

Answer 26

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

Question 27

Having no cell wall means what?

Answer 27

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.

Question 28

Describe clinical relevance of common structural differences between bacteria.

Answer 28

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