Systems for Detection of Pathogens I Flashcards
What is a commensal (non pathogen )pathogen?
β Present but not capable of causing disease in the host
What are two examples of commensal (non pathogen) pathogens?
β E.Coli
β Bacteroides thetaiotaomicron
What is a zoonotic pathogen?
β Present but only capable of causing disease in another host
What is an example of a zoonotic pathogen?
β E.Coli O157:H7
What is a commensal opportunist pathogen?
β Present and capable of causing disease in the host but only in certain circumstances
What are two examples of opportunist commensal pathogens?
β Bacteroides fragilis
β Coagulase negative staphylococcus
What are the taxonomical classifications?
β Domain β Kingdom β Phylum βClass β Order β Family βGenus β Species
What is the definition of a pathogen?
β A microbe capable of causing a specific degree of host damage
What test sites require decontamination and give two examples?
β Non sterile sites
β feces or skin
What sites must be free from contamination and give an example?
β sterile sites
β blood cultures canβt have skin flora in them
What sites require concentration and why and give 3 examples ?
β Samples with high volume or relatively low infected pathogen load
β CSF, ascites, 24 hour urine
How do you prepare cultured organisms for identification?
β Enrichment
β purification
β amplification
Why is no culture needed with direct light microscopy?
β the organisms can be seen
β it is very obvious if one of the organisms is present
What 4 organisms can be seen with direct light microscopy?
β Trichomonas vaginalis
β Schistosoma mansonii
β Strongyloides (threadworm)
β Entamoeba histolytics
What 4 organisms can be seen with direct electron microscopy?
β Rotavirus
β Rabies
β Hepatitis B
β Tonsilitis
What is another way of visualising specifically bacterial samples?
β gram staining
What are the two types of stain are used for tuberculosis?
β Ziehl Nielsen
β Auramine
What does a pathogen having a capsule mean?
β It is more likely to be a pathogen
How do you find viruses inside cells?
β Immunofluorescent staining with pathogen specific conjugated antibody
What are the 4 advantages of microscopy?
β Easy to perform
β rapid screening
β some parasites have specific morphology
β specific immunofluorescence staining is possible
What are the 4 disadvantages of microscopy?
β Not sensitive
β General stains are not specific
β Labour intensive
β requires specialist interpretive expertise
What does bacteriology rely on?
β the ability of the test system to be able to grow the pathogen
What are the three types of media bacteria can grow in?
β Non selective
β Semi selective
β Selective growth temperatures
What is an example of non selective medis?
β blood agar
What is an example of selective media?
β MacConkey agar
β DCA
β CLED
What is an example of an obligate aerobe pathogen?
β Pseudomonas fluorescens
Which pathogens can you grow in different atmospheres and why?
β S. aureus
β E.Coli
β both are facultative anaerobes
Name 4 respiratory pathogens?
β Neisseria meningitidis
β Neisseria gonorrhoea
β Haemophilus influenzae
β Brucella melitensis
In what culture can respiratory pathogens be grown?
β Microaerophilic
Why are some organisms anaerobic?
β They donβt have the capacity to deal with what oxygen does to their metabolism
What organisms are anaerobic and grow if you have frostbite?
β Clostridium perfringens
How does systematic bacteriology work?
β After performing all the tests on culture
β make a table that is either + or - for each one of the factors
β Each pathogen will get a unique pattern of - and +
What are phages?
β viruses that infect bacteria
How do you find out what concentration of antibiotic to give?
β Soak a strip in different concentrations of antibiotic
β place it on a culture of bacteria
β measure the zones of inhibition
Why can you not culture viruses?
β they live inside of cells
What is a cytopathic effect?
β Using a cell line and adding a virus to see the effect it has on cells
Why do you use the direct ELISA and not electron microscopy?
β Electron microscopy cannot identify the virus and culture takes 3-10 days
What are the 5 advantages of classical culture and identification?
β Cheap, simple, reliable β Sensitive β Validated specificity β Direct in vivo measurement of effectiveness of therapy β Easily archived
What are the 6 disadvantages of classical culture?
β Some pathogens cannot be grown
β some pathogens cannot be well differentiated by biochemistry alone
β Slow : culture requires at least overnight incubation
β some pathogens grow too slowly to aid rapid diagnosis
β labour intensive
β requires specialist interpretive experts
