Extra Qs

Question 1

Are molecular identification methods based on the organism’s genotype or phenotype. And what about biochemical tests

Answer 1

• Molecular identification = genotype

- Biochemical = phenotype

Question 2

What does a PCR test do. And the 3 main steps

Answer 2

• Amplifying specific regions of DNA

- Denaturing, annealing, elongation

Question 3

What does Lancefield group system do

Answer 3

Lancefield grouping is a system of classification that classifies catalase-negative Gram-positive cocci based on the carbohydrate composition of bacterial antigens found on their cell walls

Question 4

Name some bacteria that can be cultured on blood agar

Answer 4

strep pyogenes, hameophylius influenza, Neisseria species

Question 5

What agar can bacteria that ferment lactose be selected for

Answer 5

MacConkey agar

Question 6

What agar can salmonella be cultured on

Answer 6

XLD agar

Question 7

What agar is used for urine samples

Answer 7

CLED agar

Question 8

Out of staph and strep, which lacks catalase activity

Answer 8

streptococci

Question 9

What indicator is used in urease test. If positive, what is the colour change

Answer 9

• from yellow to pink

- phenol red is used

Question 10

what indicator is used in a DNAase test. What is the colour change

Answer 10

• Toluidine blue

- turns pinkish in the presence of free nucleotides or oligonucleotides that are released by degradation of the DNA

Question 11

5 main steps in a gram stain

Answer 11

1. Heat fix bacteria to slide
2. Flood with crystal violet
3. Rinse and flood with iodine
4. Decolourise with acetone
5. Safranin counterstain

Question 12

In acidic conditions, hydroxyapatite dissolves because ions are removed from solution. Which ions are likely to be removed?

Answer 12

OH- and (PO4)3-

Question 13

Relationship of IP and Ksp at critical pH

Answer 13

They are equal

Question 14

What type of microorganism does Sabouraud dextrose select for and why

Answer 14

Fungal

Low pH of media suppresses bacterial growth

Question 15

What is the antibacterial mechanism of action of chlorhexidine?

Answer 15

Disrupts cell walls

Chlorhexidine is broad spectrum and could be bactericidal or bacteriostatic depending on the concentration

Question 16

Cultivating in an anaerobic or aerobic environment will grow the most intra oral microbes

Answer 16

Anaerobic

Question 17

What could be added to Mitis -Salivarius growth medium to make it selective for Streptococcus mitis or Streptococcus salivarius?

Answer 17

Tellurite. Growth of mitis

Question 18

What agar grows candida

Answer 18

Sabouraud agar

Question 19

What bacteria causes sore throat and inflamed pharynx

Answer 19

Streptococcus pyogenes

Question 20

Which carbohydrate is fermented in the Snyder test?

Answer 20

glucose

Question 21

what is germination

Answer 21

the process of reactivation of spore form to vegetative form

Question 22

what does Clavulanic acid do

Answer 22

Inactivates beta lactamase to prevent bacteria inhibiting the beta lactam in antibiotics. Combined with pencillins to prevents antibiotic resistance.
[Co-amoxiclav]

Question 23

name some antibacterial toothpaste ingredients

Answer 23

Chlorhexidine, essential oils, tannous fluoride, Triclosan, Cetylpyridium chloride

Question 24

name 2 spore forming species

Answer 24

clostridium and bacillus

Question 25

When culturing microorganisms on agar plates, why is it important the plate is placed in the incubator top down.

Answer 25

To stop condensation settling on the agar surface

Question 26

What is a virulence factor

Answer 26

- features of or molecules produced by bacteria, viruses, fungi and protozoa - Help pathogenic microorganisms to (1) invade the host, (2) cause disease, and (3) evade host defences

Question 27

What does a leukotoxin do and what bacteria is it produced by

Answer 27

- Toxic to leukocytes - A type of exotoxin - Aggregatibacter actinomycetemcomitans

Question 28

the 3 components of an enveloped virus

Answer 28

- Nucleocapsid - Nucleic acid (DNA or RNA) and protein shell | - Lipid layer from host with envelope glycoproteins / spike proteins

Question 29

What effect would incubating sub gingival plaque bacteria anaerobically be on the number of colonies which formed?

Answer 29

There would probably be more cfu. The reason is that the nearly all the bacteria in the mouth are either facultatives (do not need oxygen but can grow in its presence) or strict anaerobes. So, a plate incubated aerobically will only grow the facultatives whereas a plate incubated anaerobically will grow the facultatives as well as the anaerobes. However, there are some strict aerobes that would not grow anaerobically, so it is not clear cut.

Question 30

what bacteria used in Snyder test. What pH is the growth medium

Answer 30

lactobacilli pH 5 fermenting glucose and making lactic or acetate acid

Question 31

Why the number of CFU may not be the same as the number of cells in a culture

Answer 31

- Some cells may be dead/non viable - Some may be unable to grow on the particular medium - cells often tend to clump or form chains and, if not dispersed, multiple cells will make a single CFU.