microbiology

Question 1

Microbial biofilms are an important lifestyle within the oral cavity, and are associated with caries and periodontal disease.

1. Name TWO characteristics of biofilm extracellular matrix (ECM) that confers resistance from antimicrobial agents. (2 marks)

Answer 1

polysaccharide matrix that forms a protection around the microbial cells

extracellular DNA released by lysed bacterial cells helps with structural integrity and binds to antimicrobial agents and reducing their effectiveness

Question 2

2. Name TWO important bacteria clearly implicated in periodontal disease, based on Socransky’s red ‘disease’ complex. (2 marks)

Answer 2

porphyromonas gingivitis

tanerrella forsythia

treponema denticola

Question 3

3. Name TWO bacteria associated with caries development
   (2 marks)

Answer 3

streptococcus mutants

lactobacillus species

Question 4

4. What TWO key features enable cariogenic organisms to stick to enamel surfaces and autoaggregate, and to survive within an acidic environment? (2 marks)

Answer 4

adhesive properties

acid tolerance mechanisms - can adapt to low pH conditions by regulating internal pH

Question 5

5. Name TWO systemic diseases that have been shown to be associated with periodontal biofilms? (2 mark)

Answer 5

diabetes

cvs = heart diseases, stroke and atherosclerosis

rheumatoid arthritis

Question 6

The oral environment is commonly associated with a selection of different microorganisms that may or may not be surface attached.

1. What term can be used to describe the collective group of microorganisms within the oral cavity AND what are they referred to when attached to a surface?
   (1 mark)

Answer 6

oral microbiome

oral biofilm

Question 7

2. i) List the FOUR key microbial stages of caries plaque formation. (2 marks)

Answer 7

pellicle formation on tooth surface = acts as attachment site

initial colonisation = streptococcus species adhere to pellicle and colonies tooth surface and produces extracellular polysaccharides

biofilm maturation = as colonisation progresses, microcolineis develop and bacteria pro filitrates

over time. acid tolerant bacterias such as Streptococcus mutans and Lactobacillus species, become dominant and ferment dietary sugars, producing acids that lower the pH of the biofilm and lead to demineralization of the tooth enamel, ultimately resulting in caries formation.

Question 8

ii) Name TWO key virulence factors used by Streptococcus mutans to influence enamel dissolution.
(1 mark)

Answer 8

acid production

biofilm formation

Question 9

3. i) Name the bacterium associated with secondary endodontic infections
   (1 mark)
   ii) Name ONE of its key virulence factors?
   (1 mark)

Answer 9

enterococcus faecalis

ability to form biofilms

Question 10

4. i) Why is it difficult to determine causality from a specific bacteria in endodontic infection? (1 mark)

Answer 10

they are typically polymicrobial, they involve multiple bacterial species and it’s hard to isolate a single bacterium

Question 11

ii) Which antimicrobial is primarily used to disinfect the root canal?
(1 mark)

Answer 11

sodium hypochlorite

Question 12

5) i) What culture independent technique could be used to assess changes in the oral microbial populations following antibiotic exposure? (1 mark)
ii) What is the limitation of this approach?
(1 mark)

Answer 12

16S rRNA gene sequencing

it provides information about the composition of microbial populations based on DNA sequencing but does not distinguish between live and dead bacteria
hard to capture changes or alterations in microbial activity

Question 13

Candidal infection can be associated with morbidity and mortality, especially amongst the elderly and immunocompromised.

1. Name THREE forms of oral candidosis.
   (3 marks)

Answer 13

presudomembranous candiasis (thrush)

erythematous candidacies

angular chellitis

Question 14

2. What class of antifungal agent would you most commonly use to treat patients with recurrent oral candidosis?
   (1 mark)

Answer 14

triazole antifungals
e.g. fluconazole and miconazole

Question 15

3. What is the mode of action of the antifungal agent you have named as your answer to the question above?
   (2 marks

Answer 15

it interrupts conversion of lanosterol tp ergosterol via binding to fungal cytochrome P-450 and disrupting fungal membranes

Question 16

4. Name TWO resistance mechanisms that render Candida species resistant to the class of antifungal agent you have named in Q2 above?
   (2 marks)

Answer 16

over expression of efflux pumps = they remove the drug from the cell

target site alterations = mutations in enzyme and reducing affinity for azalea drugs

Question 17

5. Name ONE species other than Candida albicans that is intrinsically resistant to the class of antifungal agent named in b) above, and describe ONE way in which this species can be differentiated from Candida albicans?

(2 marks)

Answer 17

Candida kruse

it shows a training effect when exposed to fluconazole

Question 18

a) Four factors that cause candidosis? (2 marks)

Answer 18

Physiological: Pregnancy, Age, Saliva Flow
Trauma: Dentures, Burns, Infection
Haematological: Cellular Immunodeficiency, Neutropenia
Iatrogenic: Antibiotics, Catheters, Surgery
Endocrinological: Diabetes, Addisons Disease

Question 19

b) Name the organism and virulence factor that causes it? (2marks)

Answer 19

Candida albicans: Hyphae, Adhesins, Hydrolytic Enzymes

Question 20

c) 4 Key stages of biofilm formation? (2 marks)

Answer 20

Adhesion
Colonisation
Accumulation to form a Complex Community
Dispersal

Question 21

d) How would you test for this organism and suggest lab identification
method (2 marks)

Answer 21

Take a swab and culture the swab contents on Sobouraud’s Agar and if
present, candida would present as white, creamy colonies
Laboratory testing: Germ tube formation

Question 22

e) Example of antifungals (azole and polyene) and mechanism for both (2
marks)

Answer 22

Azoles e.g. Fluconazole work by indirectly targeting the ergosterol in
the fungi cell wall by interrupting the activity of the enzyme that
produces it – 14α Demethylase. It is fungistatic.

Polyenes e.g. Nystatin directly target the ergosterol and cause
perforation and leakage of intracellular contents. It is therefore
fungicidal. It has higher virulence but is less well tolerated.

Echinocandins e.g. micafungin are also fungicidal.

Question 23

d) 2 key features that enable caries bacteria to adhere and survive in
acidic environments ( 2marks)

Answer 23

Adhesins - SpaP: makes up fibrillar layer of cell wall
Binding Proteins - glucosyltransferase, fructosyltransferase, gluten
binding protein
Sugar Modifying Enzymes: fructanase, dextranase
Polysaccharides
Acid Tolerance & Adaptation:F1F0 ATPase

Question 24

15. Chlorhexidine
    a. What group does it belong to?

Answer 24

bisbiguanide

Question 25

b. Chlorhexidine mode of actions and what is it?

Answer 25

Dicationic, one cation attaches to the dental pellicle and the other
attaches to the bacterial membrane. In a low concentration it increases
the permeability of the membrane and in a high concentration it cases
precipitation of the cytoplasm and cell death

Question 26

d. 2 factors affecting substantivity.

Answer 26

absorption to oral surfaces
maintenance of antimicrobial activity
slow neutralisation of antimicrobial activity

Question 27

e. Volume, conc and freq. of CHX

Answer 27

0.2 x 10ml = 20mg 2x a day
0.12 x 15ml = 18mg 2x a day

Question 28

f. 4 indications for CHX

Answer 28

Post oral or periodontal surgery
Physically or mentally impaired
Immunocompromised patient
Short term use for specific problem and as an adjunct to oral hygiene