bacterial identification tests Flashcards
what is the motility test and what are the results
Motility is how mobile a bacteria is. a medium is stabbed with an innoculating needle. a negative test (not very motile) will result in growth only occurring along the lesion.
a positive test will have bacterial growth away from where the medium was inoculated
what does gram staining test for and what are the positive/negative results
Gram staining tests for whether the bacteria is gram positive or gram negative by a series of staining. gram positive bacteria will stain purple and gram negative bacteria will stain pink.
what is the aerobic/anaerobic test and what are the results
duplicate mediums are cultured with the same bacteria. one of the mediums is then covered with liquid paraffin to prevent oxygen.
bacteria can be: facultative anaerobes, obligate anaerobes, obligate aerobes, microaerophiles and aerotolerant anaerobes
what is the oxidase test and what is the result
this tests whether the bacteria possess the enzyme oxidase by smearing it over a filter paper with the oxidase reagent. if the test is positive then the paper will turn from brown to purple
what is the catalase test and what are the results
tests whether the bacteria has the enzyme catalase by adding the culture to a few drops of hydrogen peroxide.
if the test is positive then the bacteria will start bubbling
what is the decarboxylase test and what are the results.
tests whether the bacteria possess the decarboxylase enzyme by culturing the bacteria in a medium that contains amino acids and a pH indicator before adding liquid paraffin.
a positive result is indicated by the medium changing to an intense pink
what does Eosin methylene blue (EMB) agar test for and what do the results mean
EMB tests for whether the bacteria is gram positive or negative and tests whether the bacteria can ferment lactose.
If the organisms grows it is most likely gram negative.
if the bacteria can ferment small amounts lactose then they culture will grow pink
if the bacteria can ferment a large amount of lactose then it will appear green
if the bacteria can’t ferment lactose then it will appear colourless
what does MacConkey agar test for and what are the results
MacConkey agar tests for whether bacteria is gram positive or gram negative and whether it can ferment glucose. (similar to EMB)
MacConkey selects for gram positive bacteria so if it grows then it is most likely gram positive
If an organisms can ferment lactose then it will turn pinkish red
if not then it will take on the colour of the growth medium
what is the starch hydrolysis test and what are the results
tests for whether the bacteria can hydrolyse starch by flooding the plains with iodine.
if the bacteria cab break down starch then colourless halos will appear around the colony.
what does Mannitol Salt Agar (MSA) test for and what are the results
MSA tests for whether the bacteria is halotolerant as well as if it can ferment mannitol.
If the bacteria can grow in the salty conditions of the MSA then it is halotolerant
if the colour changes from red to yellow then the bacteria can break down mannitol.
what is the acid gas test and what is are the results
tests whether the bacteria can break down glucose into acidic products and whether the colony produces any gas.
The coloney will contain an inverted Durhams tube which will collect any gas produced, forming a bubble.
If the bacteria can produce acidic products from glucose then it the medium will change colour, usually from red to yellow
what is the Citrate utilisation test and what are the results
tests whether the bacteria can use citrate as a carbon source for energy.
a positive test is obtained by a colour change from green to Prussian blue.
what is the urease test and what are the results
tests whether the bacteria can degrade Urease by inoculating a urea broth containing a pH indicator.
If the test is positive then the broth will turn pink due to the pH rising
what is the Methyl Red / Vogues proskauer test and what are the results
tests whether the bacteria can ferment glucose, and what acid products it is able to produce.
MR test:
a positive result is obtained by a deep red colour, indicating the acids produced have a pH lower than 4.4.
VP test:
a positive result is indicated by a deep red band forming on the surface of the culture showing the presence of acetic acid.
what is a Triple Sugar Ion (TSI) agar and what are the results
TSI agars are used to differentiate different types of gram negative bacilli by inoculating a medium containing glucose, lactose/sucrose and sodium thiosulphate
If the slant of the tube is red then it only fermented glucose
if the slant is yellow then it also fermented Lactose/surcose
if the medium is black then the bacteria utilised the sodium thiosulphate to produce H2S gas
if any cracks form in the medium then gas is being produced
