Prof Barer

Question 0

What are the two main ways of staining bacteria?

Answer 0

1). Acid fast stain
Used for mycobacterium to detect and classify

2). Gram stain
Those with thick peptidoglycan walls retain the dye (positive) whereas those without/with only thin walls will not (negative)

Question 1

Why are bacteria difficult to stain and visualise?

Answer 1

Insufficient magnification - oil is needed to exclude air between lense and object at 100x

Stain poorly with H&E

Bacteria are removed during slide preparation

Question 2

What are the 4 shapes of bacteria and the 3 variations of these?

Answer 2

Shapes:
Cocci
Bacilli/rods
Streptococci/coccobacilli
Diplococci

Variations:
Curved
Spiral
Filamentous

Question 3

What clinical importance do cell walls have in bacteria?

Answer 3

They can be exploited by antibiotics
Allow detection via gram/acid fast staining
Have endotoxin effects (e.g. Lipopolysaccharide is a toxin released only upon destruction of the bacterial cell wall)

Question 4

What are 4 external features of bacteria?

Answer 4

Flagella - aid mobility
Pilli - allow attachment
Capsule - protect against phagocytosis
Outer membrane – may have a LPS layer = toxic

Question 5

Which are the gram positive cocci bacteria and the conditions they cause?

Answer 5

Staphylococcus aureus - meningitis, impetigo
Streptococcus pyogenes - impetigo, TSS
Streptococcus pneumonaie - pneumonia
Group B streptococcus - GBS (complications e.g. Meningitis)

Question 6

What are the gram positive bacilli bacteria and the conditions they cause?

Answer 6

Clostridium difficile - AAD, pseudomembranous colitis

Clostridium perfringen - food poisoning, gas gangrene

Question 7

What are the gram negative diplococci bacteria and the conditions they cause?

Answer 7

Neisseria gonnorrhoea - gonnorrhoea

Neisseria meningitidis - meningitis

Question 8

What are the gram negative bacilli?

Answer 8

Salmonella spp - salmonella
Escherichia coli - gastroenteritis
Shigella - dysentery

Question 9

What are the bacteria which don’t stain with gram staining?

Answer 9

Mycobacterium TB - TB
Mycobacterium leprae - leprosy
Chlamydia

Question 10

How do bacteria replicate?

Answer 10

Binary fission

Question 11

What is the clinical importance of biofilm, broth turbidityand colonisation?

Answer 11

Biofilm - bacteria adhere to surfaces e.g. IV lines
Broth turbidity - allows sensitive detection of infection, especially in fluid filled cavities
Colonisation - allows us to count, identify and work out the speed at which the bacteria grows.

Question 12

What is the cell envelope of bacteria?

Answer 12

The plasma membrane, cell wall and outer membrane if the bacteria has one.
In acid fast bacteria, this is neither gram positive or negative.

Question 13

Why do mycobacterium have no gram stain?

Answer 13

Cell wall has a high lipid content = retain no stain (gram negative often retain a second stain added)

Question 14

What is the structure of viruses?

Answer 14

DNA is surrounded by a protein capsid. This may then be enveloped. The outermost layer (capsid or envelope) contains ligands.

Question 15

What forms can the genetic n formation in a virus take?

Answer 15

ssRNA
--> + sense = can be used to form mRNA and therefore be translated
--> - sense = can't form mRNA and can't be translated
ssDNA
dsRNA
dsDNA
Linear 
Circular

Question 16

What is an infection?

Answer 16

Multiplication of a pathogenic microbe within a susceptible host with associated damage or dysfunction

Question 17

How do viruses infect cells?

Answer 17

1) . Host cell must contain a receptor to the viruses ligand = virus binds
2) . Virus is taken into the cell via receptor mediated endocytosis, a coated pit or by fusing with the membrane.
3) . Virus can then translate its DNA into viral proteins.

Question 18

How are viral proteins released?

Answer 18

1) . Cell lysis

2) . Budding - capsid and viral proteins push into cell membrane, and part is pinched off.

Question 19

What are the 4 categories of viral classification and examples for each?

Answer 19

1) . DNA enveloped
- Hep B
- Herpes
2) . DNA non enveloped
- Papilloma virus
3) . RNA enveloped
- Rubella
- HIV
4) . RNA non enveloped
- Hep A
- Polio

Question 20

What is the Baltimore scheme and how does it work?

Answer 20

It is a way of classifying viruses based on the relationship between their viral genome and mRNA used for translation during expression of this genome.

Question 21

How big are viruses?

Answer 21

18-350nm

Question 22

How can viruses be diagnosed?

Answer 22

Culturing
Detection of viral antigens e.g. In blood
Detection of viral nucleus acids e.g. Via PCR

Question 23

How do viruses replicate?

Answer 23

1) . They enter the host cell, are uncoated and after making a few viral proteins, may inject their DNA into the host DNA, or form an episome. The host cell then replicates this.
2) . They enter the cell, are uncoated and replicate their own nuclei acids. New viruses are then reassembled for this DNA before being released.

Question 24

How can infection spread?

Answer 24

From animals
Water borne
Food contamination
Person to person

Question 25

What are the two types of infection?

Answer 25

Exogenous - arises from the invasion of pathogenic bacteria

Endogenous - the bodies natural micro iota become pathogenic

Question 26

How can you control infection?

Answer 26

Eliminate the reservoir
Isolate or protect the susceptible host
Eliminate the mode of transmission

Question 27

How are Henle-Kochs postulates carried out?

Answer 27

Isolate the microorganism from the diseased animal.
Propagate the microorganism in vitro.
Insert the culture into a healthy animal.
Cultivate the microorganism again from the healthy animal which has then turned diseased to prove it is the same agent.

Question 28

What are the issues with performing Henle-Kochs postulates?

Answer 28

Unethical to give a creature a disease
Some microbes don’t grow in labs
Some diseases require more than one microbe to manifest

Question 29

What is the reservoir and immediate source of an infection?

Answer 29

Reservoir - where the microbe is normally found

Immediate source - where it can be found in contact with humans

Question 30

What is the equation for the incidence of colonisation in patients?

Answer 30

R0 - 1
Y0 = ——–
R0 + Rn

Question 31

What is R0?

Answer 31

If R0 is greater than 1 the infection takes hold, if it is less than 1, it doesn’t.

R0 = (time period of infectivity) x (no. Infected people the infected individual had contact with during time period of infectivity) x (transmission coefficient)