Systems For Detecting Pathogens Flashcards
What is the taxogenic ladder after species?
Strain
Type
Isolate
What are the types of pathogens?
Commensal non-pathogen
Zoonotic non-pathogen
Commensal opportunist
What is a commensal non-pathogen?
Present but not capable of causing disease in the host
What is a zoonotic non-pathogen?
Present but only capable of causing disease in another host
What is a commensal opportunist?
Present and capable of causing disease in the host in certain circumstances
What is a pathogen?
Microbe capable of causing a specific degree of host damage
What is good sample practice?
Sterile sites should be free from contamination
Non-sterile sites require decontamination of normal flora
Samples with high volume or low infected pathogen load require concentration
What is direct light microscopy used to detect?
Threadworms, entamoeba histolytica, trichomonas vaginalis, schistosoma mansonii
What is direct electron microscopy used for?
Viruses
What colour do gram positive bacteria stain?
Blue
What colour do gram negative bacteria stain?
Pink
Are there bacteria that don’t stain?
Yes (TB for example)
What are the types of media?
Non-selective
Semi-selective
Selective growth temperatures
What are examples of non-selective media?
Blood, agar
What are examples of semi-selective media?
DCA, CLED
What are some selective atmospheres?
Aerobic
Microaerophilic
Anaerobic
What are the different types of test system in bacteriology?
Media
Selective atmospheres
Selective temperatures
Specific haemolysis of blood
What is a phage?
Virus that infect bacteria
What is strand displacement amplification?
Essentially PCR
What does molecular gene targeting aim to do?
Detect a gene or gene products that are pathogen specific
What genes are suitable targets for PCR?
Constitutive Virulence Antibiotic resistance Pathogenic phenotype Repetitive
How can you tell if the molecular test for one gene is good enough?
Specificity Reliability Sensitivity Accuracy Rapidity
How do you do bio-signature profiling?
Mass spectrometry
Isolate organism
Lyse with crystallising matrix
Ionise and detect time of flight for each particle
Calculate daltons for each protein produced
Compare against an archival database
What are the advantages of MALDI-TOF profiling?
Rapid and specific identification
What are the disadvantages of MALDI-TOF profiling?
Requires pure culture
Requires rigorous calibration and protocol standardisation
Will only identify known profiles
What are biomarkers of virulence?
Looking for selected genes or gene products that drive the disease process
What are the advantages of serotyping?
Good specificity and sensitivity
Easily automated
What are the disadvantages of serotyping?
Slow
Can be in response to previous exposure
Some antibodies are cross-reactive
Virulence is only inferred by biomarker presence
Infected into an animal model can prove virulence
What are the advantages of molecular detection methods?
Rapid
Allows fast, accurate treatment
High sensitivity
Can be automated/ used at point of care
What are the disadvantages of molecular detection methods?
Expensive Doesn’t screen for unknown Needs expertise Labour intensive Possibility of contamination Complex methods needed
