Week 1 Lecture 3 Flashcards
what is the bacterial structure?
Bacteria composes of a capsule/slime layer (also called glycocalyx (sugar coat) that surrounds the cell wall. This capsule is usually made up of polysaccharides, sometimes polypeptides or even both. This capsule/slime layer enables bacteria to attach to surfaces and to form biofilms. This coat is made inside the cell then excreted (exopolysaccharide). When this layer is arranged in a tight matrix that doesn’t allow some dyes to permeate it, it is referred to as a capsule. A slime layer is more loosely arranged. This capsule has a flagellum and pili or fimbriae. Behind the cell wall is the cytoplasmic membrane which contains three: the ribosomes, endospore and the chromosome (DNA). Notice how DNA just floats around. It doesn’t have a nuclear membrane. Flagellum for swimming. Spore enables the bacteria to survive boiling (or heat), pili or fimbriae is like Velcro, it captures things.
Outline the benefits to bacteria and the disadvantages to humans of biofilms
Encapsulated bacteria are more difficult for the immune system to recognise and destroy (
Bacillus anthracis (anthrax) has a capsule made of protein that prevents destruction by the host immune system)
Biofilm formation allows cells to resist physical forces of removal, to resist attack by host immune system, and protects from the action of antibiotics
Biofilm formation a major problem in hospitals, e.g. on catheters or dental plaque
Q. Why is protein significant?
Protein is a very good way of turning on the immune system. We often make antibodies to these hairy structures therefore stopping them from attaching.
Illustrate the types of bacterial flagella and why movement occurs
Flagella have different arrangements on the bacterial cell:
- Monotrichous (mono meaning one)
- Polar flagella are attached at one or both ends (Polar will be used like the earths poles at both ends)
- Peritrichous flagella (peri – around, trichous – hair) arranged at many locations around the cell (Peri will remind you of perimeter)
Describe two different ways to detect motility and explain the terms Brownian motion and streaming
- A hanging drop test where two types of motions are observed:
Brownian motion – not motility, caused by bacteria colliding with water molecules
Streaming – not motility, caused by currents in the drop of water
True motility – bacteria will move in different directions, not all in the same direction
- Semi-solid agar media (e.g. Craigie tube) can be used:
Motile bacteria will show diffuse growth through the tube, media will be opaque throughout the tube
Non-motile bacteria will only grow at the inoculation point, the rest of the media will remain transparent
Define the terms endospore and vegetative cell
Some bacteria produce endospores by a process known as sporulation
An endospore is a cell within the vegetative cell that is highly resistant to heat/cold, dehydration, UV radiation and chemicals
Endospore-forming bacteria most commonly found in soil – e.g. Bacillus, Clostridium
Endospores don’t stain with basic microbiological dyes
Endospore structure different to the vegetative cell, has several outer layers of protein, a cortex of peptidoglycan and the core containing cytoplasmic membrane, DNA, ribosomes
Endospores contain dipicolinic acid, forms a complex with calcium ions in the cell
Complex helps to dehydrate the endospore and protect the DNA
A mature endospore contains 10-25% of the water content of a vegetative cell, cytoplasm forms a gel, helps in heat resistance
Sporulation is initiated when vegetative cells are lacking essential nutrients, e.g. carbon or nitrogen
Spores are activated e.g. by heat, will germinate rapidly in presence of certain nutrients, outgrow to form vegetative cells
see onenote for illustration
Explain why we use an acid-fast stain to microscopically see Mycobacteria spp.
Mycobacteria (e.g. M. tuberculosis) have surface lipids of mycolic acid - not readily gram-stained (must use acid-fast stain)
The presence of motility is demonstrated in the Cragie tube test by:
a. The production of gas bubbles
b. A colour change
c. Growth at the site of inoculation only
d. Growth/Turbidity throughout the medium
e. Growth of single colonies
d. Growth/Turbidity throughout the medium
What cellular structure possessed by N. gonorrhoeae allows it to adhere to host membranes and cause infection?
a. A capsule
b. Fimbriae
c. Flagella
d. Endotoxin
e. Plasmid
B. Fimbriae
Which of the following cellular components allows genetic material to be transferred by conjugation?
a. Fimbriae
b. Flagella
c. Cell wall
d. Pili
e. Phages
d. Pili
You perform a hanging drop motility test on Klebsiella and you see the cells moving around the same spot. This indicates:
a. The bacteria are motile
b. The bacteria are motile but may have come from an old culture
c. The bacteria have short flagella and cannot move far
d. Flagella may have been damaged by shaking the culture too forcefully
e. Brownian motion
e. Brownian motion
What is Brownian motion?
a. Bacterial motility in the direction of an attractant
b. Bacterial motility away from a repellent
c. Bacterial motility in random directions
d. Refers to the rotating action of flagella
e. Occurs when molecules in a solvent bump into bacterial cells
e. Occurs when molecules in a solvent bump into bacterial cells
The movement of bacteria in the direction of light is known as:
a. Photosynthesis
b. Phototaxis
The conversion of a spore to a vegetative cell is known as:
a. Germination
b. Vegetation
c. Sporulation
d. Phosphorylation
e. Transformation
a. Germination
Five different types of bacteria are exposed to UV radiation for 90 seconds. Which would you expect to survive?
a. A gram-negative cell such as E. coli
b. A gram-positive cell such as Staphylococcus
c. A gram-negative environmental isolate of Serratia
d. A water loving gram-negative isolate of Pseudomonas
e. A spore-forming bacteria such as Bacillus
e. A spore-forming bacteria such as Bacillus
Mycolic acids prevent Gram stain penetration and are found in the cell walls of:
a. Staphylococcus
b. E. coli
c. Mycobacterium
d. Bacillus
e. Streptococcus
c. Mycobacterium
Mycobacterium can best be described as:
a. gram-positive bacilli
b. gram-negative bacilli
c. acid-fast bacilli
d. resistant to all stains because their cell wall is full of lipids
e. lacking a cell wall
c. acid-fast bacilli
The loose unstructured arrangement of glycocalyx around a prokaryotic cell is known as:
a. A slime layer
b. Capsule
c. Peptidoglycan
d. Biofilm
e. Cell wall
a. A slime layer
Which of the following is not true about biofilms?
a. They grow on surfaces
b. They are associated with nosocomial infections through their growth on medical devices
c. Help bacteria resist host immune system defences
d. They are easily removed by physical forces
e. They protect bacteria from the effect of antibiotics
d. They are easily removed by physical forces
Which of the following helps to protect a bacterium from phagocytosis by the hosts immune system:
a. Peptidoglycan
b. Capsule
c. Cell membrane
d. Pili
e. Endospores
b. Capsule
Which of the following is not true regarding bacterial endospores?
a. Produced inside a vegetative cell
b. Consist of several layers
c. Are able to stay dormant for years
d. Contain dipicolinic acid
e. Contain a greater water content then vegetative cells
e. Contain a greater water content than vegetative cells
Endospores are advantageous to the bacteria because:
a. They increase the pathogenicity of the microorganism
b. They protect microorganisms from being attacked by a hosts immune system
c. They are extremely resistant to heat
d. They allow a microorganism to survive when environmental conditions are not favourable
e. Both (c) and (d) are most correct
e. e. Both (c) and (d) are most correct being:
They are extremely resistant to heat They allow a microorganism to survive when environmental conditions are not favourable
In a Gram stain you see gram-positive bacilli that contain unstained regions the microorganism. This could be:
a. A capsule around Staphylococcus
b. A capsule around Streptococcus
c. A spore inside Clostridium
d. Slime around E. coli
e. Slime around Pseudomonas
a. A capsule around Staphylococcus
What is the function of peptidoglycan in prokaryotic cells:
a. Carbon storage as an energy source
b. Water storage preventing cells from becoming dehydrated
c. A buffer maintaining pH of the cell
d. Adds strength and shape to the cell wall
e. Allows bacteria to float
D. adds strength and shape to the cell wall
