Infectious Agents

Question 1

Describe the structure of viruses

Answer 1

Small - 20-300nm
Have DNA or RNA (not both)
No cytoplasm
Have a protein coat (caspid) - made of capsomeres (individual units)
Surrounded by envelope from host membrane

Question 2

Give examples of community acquired viruses and hospital-acquired viruses

Answer 2

Community - rhinovirus, influenza, adenovirus, rotavirus, norovirus

Hospital - norovirus

Question 3

Describe the structure of bacteria

Answer 3

Prokaryotic 
Size - 0.5-3um 
No mitochondria 
Haploid, circular DNA 
Has cytoplasm and cell wall

Question 4

Describe gram +ve and gram -ve bacteria

Answer 4

Gram +ve - lipid bilayer, attached to bilayer are lipoteichoic acids, they go through the cell wall. Cell wall is thick and made of peptidoglycans

Gram -ve - two lipid bilayers separated by a thin cell wall (peptidoglycans). 2nd bilayer has antigens attached to it (polysaccharides)

Question 5

How do we tell the difference between gram +ve bacteria and gram -ve in immunostaining?

Answer 5

Gram +ve = purple

Gram -ve = red

Question 6

How do bacteria grow? and what do they need to grow?

Answer 6

Grow by binary fission (usually every 20-30mins) - they double each time they divide

Carbon, water, nitrogen
Nutrients and minerals
Correct pH, osmotic pressure, temperature (most between 35-37) and atmosphere (oxygen or no)

Question 7

What types of bacteria can grow in oxygen?

Answer 7

Strict aerobes

Facilitative anaerobes

Question 8

What types of bacteria grow in the absence of oxygen?

Answer 8

Strict anaerobes

Microaerophiles

Question 9

Give examples of community acquired and hospital acquired bacteria

Answer 9

Community - UTIs by E. coli, pharyngitis by S. pyogenes

Hospital acquired - post-op wound infections by S. aureus, ventilator associated pneumonia by psuedomonas aerugionsa

Question 10

Describe the structure of fungi

Answer 10

Size - over 2um 
Eukaryotic 
Haploid or diploid DNA 
Single/multiple nuclei 
Chitinous cell wall 
Can be multicellular (mushrooms) or single cellular (yeast)
Can be dimorphic

Question 11

How to class fungi?

Answer 11

Based on reproduction:
Sexual - teleomorph
Asexual - anamorph

Based on type of infection:
Superficial mycoses - skin, nail, hair, mucous membrane e.g. ringworm
Subcut mycoses - mycetoma
Systemic mycoses - histoplasmosis

Question 12

Describe the structure of protazoa

Answer 12

Eukaryotic 
Single celled
Size - 5u-300um 
Single/multiple nuclei 
Haploid DNA 
Moyphology can vary throughout life 
Can have flagella

Question 13

Give an example of protazoa

Answer 13

Plasmodium sp = malaria

Question 14

Describe the structure of helminths

Answer 14

Multicellular
Parasitic worms
Different morphology and size according to stages of growth

Question 15

Describe the three groups of helminths

Answer 15

Cestodes = tapeworms - Taemia saginata
Trematodes = flatworms/flukes - Schistosoma haematobium
Nematodes = roundworms - Ascaris lumbricoides

Question 16

Which microbes can be seen using light microscopy?

Answer 16

Bacteria, fungi and protozoa

Question 17

Which microbes can be seen using electron microscopy?

Answer 17

Viruses

Question 18

What are the two main morphologies of bacteria?

Answer 18

Cocci = spherical e.g. strept/staph
Rods/bacilli = cylindrical/sausage shaped e.g. E. coli

Arrangement can be single, in pairs (diplococci), chains (streptococci) or clustered (staphylococci)

Other shapes can include spiral or helical e.g. Vibrio or Spirochaete