microbiology Flashcards
Microbial biofilms are an important lifestyle within the oral cavity, and are associated with caries and periodontal disease.
- Name TWO characteristics of biofilm extracellular matrix (ECM) that confers resistance from antimicrobial agents. (2 marks)
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
- Name TWO important bacteria clearly implicated in periodontal disease, based on Socransky’s red ‘disease’ complex. (2 marks)
porphyromonas gingivitis
tanerrella forsythia
treponema denticola
- Name TWO bacteria associated with caries development
(2 marks)
streptococcus mutants
lactobacillus species
- What TWO key features enable cariogenic organisms to stick to enamel surfaces and autoaggregate, and to survive within an acidic environment? (2 marks)
adhesive properties
acid tolerance mechanisms - can adapt to low pH conditions by regulating internal pH
- Name TWO systemic diseases that have been shown to be associated with periodontal biofilms? (2 mark)
diabetes
cvs = heart diseases, stroke and atherosclerosis
rheumatoid arthritis
The oral environment is commonly associated with a selection of different microorganisms that may or may not be surface attached.
- 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)
oral microbiome
oral biofilm
- i) List the FOUR key microbial stages of caries plaque formation. (2 marks)
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.
ii) Name TWO key virulence factors used by Streptococcus mutans to influence enamel dissolution.
(1 mark)
acid production
biofilm formation
- i) Name the bacterium associated with secondary endodontic infections
(1 mark)
ii) Name ONE of its key virulence factors?
(1 mark)
enterococcus faecalis
ability to form biofilms
- i) Why is it difficult to determine causality from a specific bacteria in endodontic infection? (1 mark)
they are typically polymicrobial, they involve multiple bacterial species and it’s hard to isolate a single bacterium
ii) Which antimicrobial is primarily used to disinfect the root canal?
(1 mark)
sodium hypochlorite
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)
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
Candidal infection can be associated with morbidity and mortality, especially amongst the elderly and immunocompromised.
- Name THREE forms of oral candidosis.
(3 marks)
presudomembranous candiasis (thrush)
erythematous candidacies
angular chellitis
- What class of antifungal agent would you most commonly use to treat patients with recurrent oral candidosis?
(1 mark)
triazole antifungals
e.g. fluconazole and miconazole
- What is the mode of action of the antifungal agent you have named as your answer to the question above?
(2 marks
it interrupts conversion of lanosterol tp ergosterol via binding to fungal cytochrome P-450 and disrupting fungal membranes
- Name TWO resistance mechanisms that render Candida species resistant to the class of antifungal agent you have named in Q2 above?
(2 marks)
over expression of efflux pumps = they remove the drug from the cell
target site alterations = mutations in enzyme and reducing affinity for azalea drugs
- 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)
Candida kruse
it shows a training effect when exposed to fluconazole
a) Four factors that cause candidosis? (2 marks)
Physiological: Pregnancy, Age, Saliva Flow
Trauma: Dentures, Burns, Infection
Haematological: Cellular Immunodeficiency, Neutropenia
Iatrogenic: Antibiotics, Catheters, Surgery
Endocrinological: Diabetes, Addisons Disease
b) Name the organism and virulence factor that causes it? (2marks)
Candida albicans: Hyphae, Adhesins, Hydrolytic Enzymes
c) 4 Key stages of biofilm formation? (2 marks)
Adhesion
Colonisation
Accumulation to form a Complex Community
Dispersal
d) How would you test for this organism and suggest lab identification
method (2 marks)
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
e) Example of antifungals (azole and polyene) and mechanism for both (2
marks)
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.
d) 2 key features that enable caries bacteria to adhere and survive in
acidic environments ( 2marks)
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
- Chlorhexidine
a. What group does it belong to?
bisbiguanide
b. Chlorhexidine mode of actions and what is it?
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
d. 2 factors affecting substantivity.
absorption to oral surfaces
maintenance of antimicrobial activity
slow neutralisation of antimicrobial activity
e. Volume, conc and freq. of CHX
0.2 x 10ml = 20mg 2x a day
0.12 x 15ml = 18mg 2x a day
f. 4 indications for CHX
Post oral or periodontal surgery
Physically or mentally impaired
Immunocompromised patient
Short term use for specific problem and as an adjunct to oral hygiene
