L2 Medical Microbiology

Question 1

What causes thrush?

Answer 1

Candida - Fungi

Question 2

What causes malaria?

Answer 2

Protozoa

Question 3

A tape worm is an example of what?

Answer 3

Helminths

Question 4

Prokaryotes

Answer 4

No nucleus/membrane bound organelles
Genome - single/circular DNA, haploid, non-genomic DNA
Peptidoglycan cell wall

Question 5

Eukaryotes

Answer 5

Membrane bound nucleus
Genome: chromosomes in nucleus/diploid
80s ribosomes
No cell walls

Question 6

Aerobes bacteria

Answer 6

Use O2 as final electron acceptor (very efficient)

E.g. oxidation of glucose to CO2 and H2O

Question 7

Anaerobes bacteria

Answer 7

Fermentation - final electron acceptor is organic molecule
E.g. glucose to lactic acid
ok when substrates are plentiful
Oxygen is usually toxic to anaerobic bacteria

Question 8

Bacteria lacking cell walls

Answer 8

Mycoplasma (pneumoniae)

Chlamydia (trachomatis)

Question 9

Bacterial envelope structure

Answer 9

Determines gram staining/antibiotic susceptibility

LPS only Gram -ve

Question 10

Exotoxin

Answer 10

Botulism toxin

Question 11

Peptidoglycans

Answer 11

Three dimensional polymer
N-acetylated sugars
glucosamine (NAG) and muramic acid (NAM)
and
3-5 amino acid peptides
AAs peculiar to peptidoglycans – resistant to enzymatic destruction
Cross-linked by transpeptidase enzymes

Question 12

How are peptidoglycan synthesised? [3]

Answer 12

Polymerisation of sugars to make the back-bone
Elongation of aa side-chains to add the peptides
Transpeptidase to cross-link

Question 13

Mycobacteria

Answer 13

Gram +ve cell wall
Doesn’t stain positive
Very thick lipid membrane (mycolic acid mycomembrane) anchored to peptidoglycan layer - intracell survival

Question 14

Capsule

Answer 14

Polysaccharide coat ‘hides’ immunogenic cell wall
Immunity requires antibodies to the capsule
Metabolic burden on the bacterium
Confers virulence e.g.
Haemophilus influenzae

Question 15

Ribosomes

Answer 15

Engines of protein synthesis
70S (sedimentation rate)
Smaller than in eukaryotes (80S)
Subunits 50S and 30S
Each contains RNA and proteins
Bacterial RNA
Target of antibiotics
Diagnostic tests

Question 16

Plasmids

Answer 16

Circular ‘extra-chromosomal’ DNA
Independently replicating
Present in many bacteria
Can code for dozens of genes
Like viruses
Passed down to progeny
Some transmitted between bacteria

Question 17

Transposons

Answer 17

DNA sequences that are able to move location in the genome.
Encode transposase 
Plus other genes
Mobile between
genomic and plasmid DNA
Plasmids
Plasmid and genomic DNA

Question 18

Bacillus spp and clostridium spp are resistant to what? TDDD

Answer 18

Drying
Temperature
Disinfection
Digestion
Important in: clinical disease pattern and infection control