What are commensal non-pathogens, zoonotic non-pathogens and commensal opportunists?
- Commensal non-pathogen - present but not capable of causing disease in host.
- Zoonotic non-pathogen - present but only capable of causing disease in another host - e.g. E. coli subclinical in cattle but pathogenic to humans.
- Commensal opportunist - present and capable of causing disease in the host, but only in certai circumstances.
Define a pathogen.
A microbe capable of causing a specific degree of host damage under certain circumstances.
Describe the advantages and disadvantages of microscopy in pathogen detection.
- Easy to perform.
- Rapid screening.
- Some parasites have specific morphology.
- Not sensitive.
- General stains are not specific.
- Expensive - labour intensive, requires specialist interpretation.
What conditions can we control in order to select for a specific microbe?
- Selective media
- Selective temperature
- Selective atmosphere
- Antibiotics - e.g. using ampicillin resistance gene
Describe the advantages and disadvantages of classical culture.
- Cheap, simple, reliable reagents.
- Sensitive - single organisms grown and identified.
- Validated specificity.
- Direct in vivo measurement of effectiveness of therapy - e.g. antibiotic sensitivity.
- Some pathogens cannot be grown.
- Some pathogens cannot be well differentiated by biochemistry alone.
- Slow - culture requires at least overnight incubation.
- Some pathogens grow slowly to aid rapid diagnosis.
- Expensive - labour intensive and requires specialist interpretation.
What are the advantages of using microarrays?
- Covers the whole genome.
- Can be used for RNA and transcriptomics.
- Can look for microRNA.
Name 4 genetic techniques for detection of pathogens.
- Gene targeting
- Genome targeting
- Targeting biomarkers of virulence
- Rapid sequencing
Describe the advantages and disadvantages of mass spectrometry (MALDI-TOF) in pathogen detection.
- Can only identify a known profile.
Describe the advantages and disadvantages of using biomarkers of virulence to detect pathogens.
- Good specificity.
- Good sensitivity.
- Easily automated.
- Serological response not rapid - not useful in acute infections.
- Single sera results are meaningless due to possible previous exposure.
- Some antibodies are cross-reactive.
- Virulence is only inferred by the presence of a biomarker - not proven.
Describe the advantages and disadvantages of using molecular detection methods to identify pathogens.
- Faster than traditional techniques.
- Allows for timely therapy and interventions.
- Increased sensitivity in positive samples.
- Can be automated and has potential for point of care testing.
- Expensive - labour intensive, requires expertise.
- Does not screen for unknowns.
- Possibility of contamination.
- Negative samples may still need culture.