Microbes

Question 1

What are the categories of microbes in size order (small - large)?

Answer 1

"Prions" (10-8)
Viruses (10-7)
Mycoplasma/chlamydiae/rickettsia  - intracellular obligates (10-6)
Bacteria (10-5)
Single cell fungi - yeasts (10-4)
Protozoa (10-4)
Multicellular fungi -aspergillus (10-3+)
Helminths (10-3+)

Question 2

Describe the Baltimore classification of viruses

Answer 2

I - dsDNA -> mRNA
II - ssDNA -> dsDNA -> mRNA
III - dsRNA -> mRNA
IV - (+)ssRNA -> (-)ssRNA -> mRNA
V - (-)ssRNA -> mRNA
VI - (-)ssRNA-RT -> DNA/RNA -> dsDNA -> mRNA
VII - dsDNA-RT -> mRNA

Question 3

Name the 3 categories of DNA viruses and a popular example for each

Answer 3

ssDNA non-enveloped:
Parvovirus 19 (common mild childhood infection - foetal abnormalities in pregnant women)

dsDNA non-enveloped:
Adenovirus, HPV

dsDNA enveloped:
Herpes, hepatitis B, molluscum contagiosum (warty growths with a spot)

Question 4

Name the 4 categories of RNA viruses and a popular example for each

Answer 4

ssRNA (+) icosahedral non-enveloped:
Coxsackievirus (aseptic meningitis), echovirus, enterovirus, hepatitis A & E, norovirus - mostly faeco-oral transmitted

ssRNA (+) icosahedral/helical enveloped:
HIV, hepatitis C, rubella, encephalitis viruses, yellow fever virus

ssRNA (-) helical enveloped:
Ebola, measles, mumps, influenza, respiratory syncytial virus

dsDNA icosahedral non-enveloped:
Rotavirus

Question 5

Some viruses are oncogenic, name one and the cancers it is commonly attributable to

Answer 5

Human Papilloma Virus (HPV) - cervical, penile and anorectal cancers

Question 6

What are bacteriophages and why are they important?

Answer 6

Viruses that affect bacteria

Involved in the horizontal transmission of bacterial genes including antibiotic resistance

Question 7

Name and describe the 3 main bacterial shapes

Answer 7

Coccus - spherical
Spirillus - spiral
Bacillus - rod-like

Question 8

Name the 3 main morphologies of bacterial colonies and the prefix used for each

Answer 8

Clusters - Staphy
Chains - Strep
Pairs - Diplo

Question 9

Describe the difference between gram positive and negative bacteria

Answer 9

Gram Positive:
All Ps - purple, positive, thick peptidoglycan cell wall

Gram Negative:
Red/pink, negative, two cell membranes (outer lipopolysacchride) with no thick peptidoglycan

Question 10

Name the 2 main mechanisms of bacterial pathogenesis

Answer 10

Virulence factors

Toxins

Question 11

What are the four main mechanisms utilised by virulence factors? Give an example of each.

Answer 11

Host entry - polysaccharide capsule
Adherence - pili, fimbriae
Invasiveness - enzymes eg collagenase
Iron sequestration - siderophores

Question 12

Why are siderophores a useful virulence factor?

Answer 12

Bind soluble Fe3+
Make it available for absorption
Iron is essential for growth and DNA replication

Question 13

What are the 2 main types of toxin and how do they differ?

Answer 13

Exotoxins - released by microbe

Endotoxins - released when microbe degenerates

Question 14

Name the 2 main categories of fungi and how they differ

Answer 14

Yeasts - single-cell organisms

Moulds - multi-cellular organisms

Question 15

Name 3 important yeasts and the conditions they are related to

Answer 15

Candida albicans - thrush
Cryptococcus neoformans - meningitis and blindness
Pneumocystis jiroveci - immunosuppressed patients marker eg HIV

Question 16

Name 2 important Moulds and the conditions they are related to

Answer 16

Aspergillus species - lung infections in immunosuppressed

Dermatophytes - ringworm, athletes foot

Question 17

What are the 2 main categories of parasites and how do they differ?

Answer 17

Protozoa - single-cell organisms

Helminths - multi-cellular

Question 18

Name 3 important Protozoa and the conditions they cause

Answer 18

Plasmodium falciparum - malaria
Trypanosoma cruzi - sleeping sickness
Giardia lamblia and cryptosporidium parvum - diarrhoea