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Flashcards in Lecture 2 - Laboratory Deck (26):

culture dependent

can grow organism in lab and study it

*Collect specimen > Isolate > Investigate / test > identify


culture independent

don't need to grow it in lab to be able to identify and study it
*collect specimen> Investigate (test) > identify


what is important when it comes to specimens collection, why?

quality. Effects speed and accuracy of organism identification.
-contributes to better pt outcomes and avoids inappropriate treatment


what types of specimens can you collect?

throat swab, sputum, blood samples (sterile), wound swabs, urine, genital swabs, stool


what is an example of a sterile specimen, why?

blood sample.
arent in contact with bacteria, virus, fungus that is all over body – no chance for cross contamination.
– able to identify bacteria and such that isnt supposed to be in there


what are important details to label on specimen collection

-sources (niches) --> can aid in identification (rash vs cat bite)
-patient status can effect work up (healthy vs diabetic)



a population of bacteria grown in defined medium and defined conditions in a laboratory


pure culture

growth of a single known species - what we want


mixed culture

holds two or more species (starting point)

-need to separate normal flora from causative agent


contaminated culture

includes unwanted microbes, usually introduced inappropriately
-living on pt but not actually the cause of infection


what is inoculation?
-how is it completed

Adding a small amount of sample (ex: urine, swab) to media to grow a culture
-only certain bacteria can grow on certain media

-Inoculated media is incubated to grow culture at 20 to 40 ºC, different atmospheres (aerobic, anaerobic)

Types of inoculation:
Streak plate (\/\/\)
Spread plate (L)

*goal is to isolate colonies


isolated colony

A population of cells on an agar plate that arise from division of a single cell
-dif species form colonies with distinct characteristics (morphology) like size and colour


what is colony morphology

-differs between species - an be used to identify causative agent
-media type also aids in identification (differential and selective or enriched)


differential media

-Contain chemicals that allow distinction of different types of bacteria based on colony morphology (d/t specific trait like metabolism)
ex) mackonkey agar - identify lactose fermentation or not


Selective Media

-prevents growth of a specific group of microbes, while allowing growth of others
-target general groups (gram + or gram - or staphylococcus)


enriched media

contains organic molecules to grow Fastidious Microbes


what are fastidious microbes

microbes that have complex nutrient requirements Ex. vitamins, growth factors
-many pathogens are fastidious and rely on their host for nutrients
ex) hemophelus influenza that causes meningitis needs heme (iron) and vitamins


what are biochemical tests?

identify bacteria based on the enzymes they produce
-test for metabolic enzymes by growing in different nutrient sources


what are immunological tests?

use antibodies to detect specific antigens that are found on microbes

- can be culture dependent or independent

-ex) O-antigen test would identify V. cholerae O139, E. coli O157


what is agglutination

-Antibodies detect and bind specific surface antigens on microbes
-Antibodies can bind multiple microbes, cause visible clumping, indicating a positive reaction


what is the reasoning behind staining

bacterial cells are clear and require staining to be visible


what are the types of stains?

Positive stain: stains the bacteria
Negative stain: stains the background
differential staining - distinguished btw bacterial toes (gram +/- stain, endospore stain)


how is investigation for independent cultures different than dependant cultures?

*important in obligate parasites (chlamydia, viruses)
-tests specific for organism
-immunological tests - detection of antigens
-molecular tests like PCR, DNA sequencing


explain PCR

-amplifies small amount of dana with specific sequence
-allows detection of causative agent even in mixed samples at low concentration
*detection of TB, chlamydia


How does PCR work in the presence of mixed samples

DNA primers bind to specific microbial DNA, an enzyme duplicated DNA by exponential application --> microbial DNA can now be detected


what is DNA sequencing?

direct identification by sequencing all DNA in a sample and comparing to data base of known organism DNA