Testing in the Diagnostic Microbiology Laboratory Flashcards
What is done during microbiology lab diagnostic testing?
Detection of pathogens Identification of pathogens Antimicrobial susceptibility testing
What is the emphasis of microbiological testing?
Quick diagnosis
What are the types of lab tests?
Microscopy Culture Detection of microbial components Serology
What are the types of microscopy?
Bright field Dark field Phase contrast Fluorescence Electron
What is bright field micrscopy?
Sample illumination is transmitted (i.e., illuminated from below and observed from above) white light, and contrast in the sample is caused by attenuation of the transmitted light in dense areas of the sample.
What kind of microscopy is used for gram stains?
bright field microscopy
What is dark field microscopy?
Using a dark background and allowing light to bend on the organism and into the eye piece making the organism show up on a black background
What is phase contrast microscopy?
Similar to bright field but 2 lights shine through with a phase difference of 1/4 wavelength
What is fluorescence microscopy?
Fluorescent light is shone onto labelled molecules to create a light image of the slide
How is the electron beam focused in electron microscopy?
Using magnets
How is the sample prepared on electron microscope?
It is prepared on a metal grid that is 3mm in diameter
What influences resolution in microscopy?
The wavelength
What is the purpose of culturing bacteria?
To determine if pathogens are present To provide enough of the organism to perform tests on To perform antibiotic susceptibility testing
How do lab staff determine which bacteria to culture for?
They use knowledge of the location that the specimen was taken from
How do lab staff determine which bacteria to culture for?
They use knowledge of the location that the specimen was taken from. (eg sputum: S.pneumoniae, h. influenzae) Doctors also make requests for ordering the tests. However, a particular set of conditions will not suit all pathogens. Instead particular culture conditions must be used.
What conditions must be accounted for when looking for pathogens using cultures?
Nutrition requirements Gaseous atmosphere Incubation time and temperature
What must be done when looking for an unusual pathogen?
Lab must be informed of special microscopy or stains as well as any special culture conditions. If you don’t know what you are looking for you must provide good clinical information on the request form. Specialists can also be called and asked about these situations.
How are bacteria identified in the lab?
Traditionally bacteria are identified using biochemical tests (based on enzymes possessed by bacteria) eg: catalase, coagulase, and oxidase tests
How are biochemical tests conducted?
Set of tests conducted (test kits) and the pattern of positives and negatives forms a number which correlates to a code and a diagnosis. Kit can also be added onto a vitek card and in turn a machine.
What is a MALDI-TOF?
It is a type of mass spectroscopy
How does MALDI-TOF work?
Bacterial suspension from colony is inoculated onto a steel plate and put into a machine and a laser beam shines on the plate from well to well and breaks up proteins in the bacteria and the speed they get to the ion detector depends on their mass and the mass achieved is compared to a database.
What microbial components can be used for diagnosis?
Antigens and nucleic acids
What is serology?
Detection of specific antibodies to a microorganism in the serum
Why is microscopy and culture not practical for some pathogens?
Can’t be visualized under microscope using routine stains (eg chlamydia and mycoplasma) Too small for routine microscopy (viruses) Grow too slowly Too difficult to grow in labs Microscopy and culture not sensitive enough
