Microbiology 1- Bacterial properties

Question 1

What is seen when you add dye to gram + and gram- bacteria

Answer 1

Gram positive bacteria:
Peptidoglycan in cell wall retains dye.
High peptidoglycan = deep violet

Gram negative bacteria:
Dye is lost from thinner peptidoglcan
The cells absorb counterstain making them appear pink.

Question 2

What are two key difference between gram+ and gram- cells?

Answer 2

Gram negative bacteria have TWO MEMBRANES (inner and outer)
Gram positive only have ONE MEMBRANE

LIPOPOLYSACCHARIDE (LPS) IS ONLY PRESENT IN GRAM NEGATIVE BACTERIAL CELL WALLS

Question 3

Describe the structure of a gram + cell wall

Answer 3

You get the cytoplasmic membrane with a THICK LAYER of peptidoglycan on top which retains the dye and stains DEEP VIOLET

Question 4

Describe the structure of a gram - cell wall

Answer 4

Gram Negative - peptidoglycan is sandwiched between the inner membrane and the outer membrane

Both membranes have embedded channel proteins

Outer Membrane - composed mainly of LIPOPOLYSACCHARIDE (LPS)

Question 5

What is done after a gram stain to determine treatment (4)

Answer 5

Culture and microscopy

Biochemical and serological tests

DNA techniques such as PCR

Sensitivities to antibiotics is determined

Question 6

give 5 examples of gram negative bacteria

Answer 6

Escherichia coli (EPEC - diarrhea, EHEC - produces toxin, dysentery and kidney failure)

Salmonella (typhimurium - food poisoning, typhi - typhoid)

Shigella (dysentery)

Vibrio cholerae (cholera)

Neisseria (meningitidis- meningitis, gonorrhoeae- gonorrhea)

Question 7

Give 3 examples of gram positive bacteria

Answer 7

Staphylococcus aureus (skin diseases, endocarditis, bacteraemia, joint diseases, pneumonia)

Streptococcus pneumoniae (pneumonia, meningitis, otitis media)

Streptococcus pyogenes (tonsilitis, necrotizing fasciitis, bacteremia, scarlet fever)

Question 8

Give examples of mycobacteria

Answer 8

Mycobacterium tuberculosis (TB)

Mycobacterium leprae (leprosy)

Question 9

5 effects of a bacterial pathogen

Answer 9

• Colonize (surface structures such as pili)

• Persist (avoid, subvert, or circumvent host defenses in
or outside cells).

• Replicate (acquire nutrients such as iron, energy
sources etc)

• Disseminate within cells, tissues between organs
and hosts (bacterial and host cell motility, through
aerosols, faeces etc)

• Cause disease (produce toxins that kill host cells,
induce diarrhea, dysregulate immune responses)

Cows Protect Really Dumb Cows

Question 10

Describe three methods of surviving in the host cell

Answer 10

Prevent Fusion with Lysosomes - Salmonella, Mycobacteri and Chlamydia

Escape - Listeria and Shigella break down the vesicle and escape into the cytoplasm

Survive in Phagolysosome - Coxiella can just survive in the harsh environment inside a phagolysosome

Question 11

How does salmonella invade cells?

Answer 11

Two multi-protien machines
Flagellum
Injectisome

They polymerise actin into filaments
This ruffles the plasma membrane and bacteria get stuck in this ruffle
As the process dies down and returns to normal, the trapped bacteria is internalised

Question 12

Describe the injectisome system (3)

Answer 12

a translocon is inserted into the plasma membrane of the host cell.

By making a passage into the cell, it allows effector proteins to be transferred from the bacterial cell to the host cell.

The effector proteins lead to actin polymerisation which causes the uptake of bacteria into the host cell.

Question 13

Describe how shigella and listeria enter cells (5)

Answer 13

It breaks out of the vacuole

It then assembles/polymerises actin at one pole of the bacterial cell

This polymerisation of actin generates force which propels the bacterium through the cytoplasm

This leads to the spread of the bacterium from one cell to another

These streams of actin are known as COMET TAILS

Question 14

What are the three main mechanisms of gene transmission

Answer 14

Transformation

Transduction

Conjugation

Question 15

Describe the process of transformation (3)

Answer 15

Sucking up DNA from outside

They can recognise naked DNA (e.g. from the lysis of other bacteria)

They have transport mechanisms which allow uptake of this DNA and incorporation into the bacterial chromosome

Question 16

Describe the process of Transduction

Answer 16

When phages invade bacteria, it replicates its DNA in the bacterium and cuts the bacterial DNA into small pieces

Some bacterial DNA may be packaged into the phage heads

New phage particles are released

The phage particles injects the bacterial DNA from the previous bacterium it infected into the next bacterium.

Injected DNA may be incorporated into the bacterial chromosome.

Many Gram - and Gram + can do this

Question 17

Describe the process of conjugation

Answer 17

You get a physical bridge between bacteria which allows the transfer of a plasmid between the bacteria.

Question 18

What does pathogenicty island mean

Answer 18

Horizontally Acquired DNA that contributed to Virulence