Direct Methods of Analysis. Flashcards
(42 cards)
What are the 3 steps in the direct method of identifying bacteria?
Identify bacteria via microscopy.
Culture bacteria.
Carry out antimicrobial sensitivity test on cultures.
What 8 steps are carried out when directly analysing bacteria?
Direct smear.
Culture the sample.
Analyse colony morphology.
Apply differential tests e.g.
Gram stain.
Perform preliminary tests e.g. oxidase or catalase tests.
Biochemical tests (conventional or commercial).
Antibiotic sensitivity.
How do we perform a direct smear so we can view a sample under the microscope?
By smearing some of the sample onto a microscopic slide.
Why do you stain samples before you view them under the microscope?
So it is easier to view under the microscope.
How do you culture a bacterial sample?
You smear some of the sample onto a nutrient agar such as blood agar or MacConkey agar.
How can growing a bacterial strain on a growth media help you to identify the strain of bacteria?
You can subject the agar and sample to different conditions.
E.g. by depriving it of oxygen etc.
What bacterial feature is usually analysed during microscopy?
The morphology of the culture.
What is a good example of a differential test that we can perform on bacteria?
The Gram stain which will tell us whether the bacteria are gram positive or gram negative.
What are the 2 categories of biochemical tests that we can perform on a bacterial sample?
Conventional tests.
Commercial tests.
What does antibiotic sensitivity testing allow us to do?
To see what medication works best against this bacteria.
What are the 4 types of microscopy test that we can perform to help us identify an unknown bacteria?
Wet mount.
Gram stain.
Acid fast stain.
Fluorescence testing.
What does the KOH test tell us about a bacteria?
If the bacteria uses oxygen.
What is a positive KOH test?
Bacteria that utilise O2 will produce bubbles.
What does the wet mount technique involve?
Placing the sample on a microscope slide with solution.
You then view the sample through the microscope.
How is the Gram stain carried out?
By adding certain chemicals to the sample in a particular order.
Once the sample is placed under the microscope it will either be stained pink or blue.
What colour do gram negative bacteria turn after being gram stained?
Pink is always gram negative.
What colour do gram positive bacteria turn after being gram stained?
Blue is always gram positive.
Why can there sometimes be both gram negative and gram positive bacteria in the same sample?
As there may be more than 1 type of bacteria in each sample.
Acid fast stains are used to identify what kind of bacteria?
Mycobacterium tuberculosis.
What does the fluorescence technique involve?
A specialised microscope which emits fluorescent light.
How is the fluorescence technique carried out?
The sample is stained with a fluorescent dye that adheres to certain bacteria.
This allows us to see whether any of these bacteria are within the sample.
What are the 8 steps of the Gram stain method?
Smear onto slide.
Air dry.
Heat fix.
Stain with crystal violet and leave for 1 minute.
Add iodine.
Rinse with ethanol. (10 seconds).
Rinse with water.
Stain with safranin.
Culturing bacteria should only be done where?
In the lab.
Why should bacteria be transferred to different media within a safety hood?
So they do not contaminate the immediate area or infect the person handling them.
