Infection 2 - Introduction to Microbes

Question 1

What are the 4 main classifications of micro-organisms?

Answer 1

1) Viruses
2) Bacteria
3) Fungi
4) Parasites

Question 2

What are the relative sizes of viruses, bacteria, fungi + parasites? (smallest to largest)

Answer 2

1) Viruses - 10^-8 to 10^-7 M
2) Bacteria - 10^-6 to 10^-5 M
3) Eukaryotic cells - 10^-5 to 10^-4 (human + fungi)
4) Worms - 10^-3 to 1M

Question 3

What are 3 ways in which bacteria are classified?

Answer 3

1) Gram negative or gram positive
2) Shape - either cocci, bacilli or spirillus
3) Aerobes (survive in O2) or anaerobes (can survive without O2) - obligate means only in that environment.

Question 4

What are the different shapes bacteria can be?

Answer 4

1) Cocci - spherical, can exist in chains or clusters
2) Spirillus - spiral shaped
3) Bacillus - rod shaped

Question 5

What are the differences between gram-negative and gram-positive bacteria?

Answer 5

Gram negative = have an outer membrane, have 1 or few layers of peptidoglycan in cell wall.

Gram positive = lack an outer membrane, have many layers of peptidoglycan in cell wall.

Question 6

How does a gram-stain work + distinguish between gram positive + negative bacteria?

Answer 6

• Apply crystal violet dye to sample, add iodide to trap it.
• Wash/decolour with ethanol/acetone
• Counterstain with safranin
• Gram positive (+) retain PURPLE stain colour - due to thick peptidoglycan layer
• Gram negative (-) don’t retain colour and stain PINK with counterstain - due to lack of peptidoglycan

Question 7

What are 4 ways in which viruses are classified?

Answer 7

1) Genome - is it RNA or DNA
2) Genome - is it single or double stranded
3) Genome - is it a positive or negative strand
4) Genome - is it enveloped or non-enveloped

Question 8

Do viruses have cell walls?

Answer 8

No - they are simply a protein coat encasing a nucleic acid.

Question 9

What type of cells are prokaryotic?

Answer 9

• Bacteria + Archaea (lack a nucleus)

Question 10

What are the key differences between prokaryotic and eukaryotic cells?

Answer 10

• No nucleus vs membrane bound
• No membrane-bound organelles vs present
• 70s ribosomes vs 80s ribosomes
• Circular (usually single) chromosome vs multiple chromosomes

Question 11

How are parasites classified?

Answer 11

1) Protozoa (single celled) - e.g.: plasmodium falciparum (malaria)
2) Helminths (worms, multi-cellular) - e.g.: roundworms, tapeworms + flukes

Question 12

How are fungi classified?

Answer 12

1) Yeasts (single celled) - e.g.: candida albicans

2) Molds (multi-cellular) - e.g.: aspergillus or dermatophytes