Diagnostic and typing methods Flashcards
What bacteria is associated with periodontal disease?
- Porphyromonas gingivalis
- Actinobacillus actinomycetemcomitans
- Prevotella intermedia
- Bacteroides forsythus
What bacteria is associated with dental caries?
streptococcus mutans
what bacteria is associated with root canal infections?
- porphyromonas endodontalis
- fusobacterium nucleatum
How can bacteria be detected in microbial cultures?
Culture on suitable agar medium, isolate bacteria & identify by characterisation of enzyme activities/sugar fermentation tests
How are microbiological cultures formed? (the steps)
- vortex mix sample for 30s
- serial dilutions in FAB
- spiral plate to agar media
- incubate anaerobically for 10 days
- obtain total bacteria counts
What can be used as agar media?
- Fastifious Anaerobe Agar (FAA) with defibrinated horse blood
- FAA supplemented with vancomycin
How can bacteria be identified?
- anaerobes noted by their sensitivity to metronidazole disc
- gram stain
- study the enzymatic activities & sugar fermentation
How do anaerobes respond to a metronidazole disc?
They will die
How does a gram stain differentiate between gram positive and gram negative bacteria?
Gram positive will turn purple
What is the advantage of using culture methods?
yields bacterial isolates for future testing and study
what are the disadvantages of using culture methods?
- requires viable cells
- insensitive
- only small numbers of samples can be analysed at once
- inconclusive results
- labour intensive
What is a DNA probe?
Segments of DNA that have been labelled with chemoluminescent, fluorescent or radioactive agents
What are the different types of DNA probes?
- Whole genomic (entire genome)
- Cloned gene
- Oligonucleotide (20-50 bases)
What is the 16S ribosomal RNA (rRNA) gene?
Found in ALL bacteria
- essential for survival
Why are PCR tests good?
- highly specific
- sensitive
- can be used to directly detect bacteria in clinical specimens
What are the types of PCR primers?
- general bacterial primers
- group-specific primers
- species-specific primers
What are the advantages of DNA probes & PCR tests?
- 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
What are the disadvantages of using DNA probes or PCR testing?
- May detect dead cells
- Detect only pre-selected species
Why is it important to subtype bacteria?
- track routes of transmission during disease outbreaks
- study pathogenicity of specific strains
What are the different types of molecular (genetic) typing methods?
- restriction enzyme analysis (REA)
- gene probe typing
- ribotyping
- 16S-23S intervenir spacer region
- DNA sequencing
What is restriction enzyme analysis (REA)?
Typing method that digests whole genomic DNA with restriction enzymes
what is the problem with restriction enzyme analysis?
too many DNA fragments obtained, makes interpretation difficult
How can number of DNA fragments generated by REA be reduced?
Using a suitable gene probe
When is microbial typing applied to dentistry?
- infected root canals
- tongue dorsum or subjects with halitosis
- aortic tissue of patients with heart disease
- prosthetic hip joint infections
