Diagnostic and typing methods

Question 1

What bacteria is associated with periodontal disease?

Answer 1

• Porphyromonas gingivalis
• Actinobacillus actinomycetemcomitans
• Prevotella intermedia
• Bacteroides forsythus

Question 2

What bacteria is associated with dental caries?

Answer 2

streptococcus mutans

Question 3

what bacteria is associated with root canal infections?

Answer 3

• porphyromonas endodontalis
• fusobacterium nucleatum

Question 4

How can bacteria be detected in microbial cultures?

Answer 4

Culture on suitable agar medium, isolate bacteria & identify by characterisation of enzyme activities/sugar fermentation tests

Question 5

How are microbiological cultures formed? (the steps)

Answer 5

1. vortex mix sample for 30s
2. serial dilutions in FAB
3. spiral plate to agar media
4. incubate anaerobically for 10 days
5. obtain total bacteria counts

Question 6

What can be used as agar media?

Answer 6

• Fastifious Anaerobe Agar (FAA) with defibrinated horse blood
• FAA supplemented with vancomycin

Question 7

How can bacteria be identified?

Answer 7

• anaerobes noted by their sensitivity to metronidazole disc
• gram stain
• study the enzymatic activities & sugar fermentation

Question 8

How do anaerobes respond to a metronidazole disc?

Answer 8

They will die

Question 9

How does a gram stain differentiate between gram positive and gram negative bacteria?

Answer 9

Gram positive will turn purple

Question 10

What is the advantage of using culture methods?

Answer 10

yields bacterial isolates for future testing and study

Question 11

what are the disadvantages of using culture methods?

Answer 11

• requires viable cells
• insensitive
• only small numbers of samples can be analysed at once
• inconclusive results
• labour intensive

Question 12

What is a DNA probe?

Answer 12

Segments of DNA that have been labelled with chemoluminescent, fluorescent or radioactive agents

Question 13

What are the different types of DNA probes?

Answer 13

• Whole genomic (entire genome)
• Cloned gene
• Oligonucleotide (20-50 bases)

Question 14

What is the 16S ribosomal RNA (rRNA) gene?

Answer 14

Found in ALL bacteria
- essential for survival

Question 15

Why are PCR tests good?

Answer 15

• highly specific
• sensitive
• can be used to directly detect bacteria in clinical specimens

Question 16

What are the types of PCR primers?

Answer 16

1. general bacterial primers
2. group-specific primers
3. species-specific primers

Question 17

What are the advantages of DNA probes & PCR tests?

Answer 17

• less time consuming
• very sensitive
• can directly detect bacterial DNA within clinical samples
• do not require viable cells (samples do not have to be analysed immediately)
• can detect uncultivable species

Question 18

What are the disadvantages of using DNA probes or PCR testing?

Answer 18

• May detect dead cells
• Detect only pre-selected species

Question 19

Why is it important to subtype bacteria?

Answer 19

• track routes of transmission during disease outbreaks
• study pathogenicity of specific strains

Question 20

What are the different types of molecular (genetic) typing methods?

Answer 20

• restriction enzyme analysis (REA)
• gene probe typing
• ribotyping
• 16S-23S intervenir spacer region
• DNA sequencing

Question 21

What is restriction enzyme analysis (REA)?

Answer 21

Typing method that digests whole genomic DNA with restriction enzymes

Question 22

what is the problem with restriction enzyme analysis?

Answer 22

too many DNA fragments obtained, makes interpretation difficult

Question 23

How can number of DNA fragments generated by REA be reduced?

Answer 23

Using a suitable gene probe

Question 24

When is microbial typing applied to dentistry?

Answer 24

• infected root canals
• tongue dorsum or subjects with halitosis
• aortic tissue of patients with heart disease
• prosthetic hip joint infections