Microbiology Flashcards
initial step in identifying bacteria
gram stain
benefits of quick stain
quick and easy
results of gram stain
positive - purple
negative - red
example of gram -ve
E coli
example of gram +ve
staphylococcus aureus
gram stain protocol
pick up colony using sterile plastic loop and make suspension on slide with drop of PBS water
dry with hairdryer
place slide on staining rack
add crystal violet to cover slide and leave for 1min
rinse with tap water
cover with alcohol - decolourise soln - leave 10s
immediately rinse with tap water
cover with safranin leave for 1min
gently rinse with tap water
blot excess liquid with tissue
inspect
what can be seen ny microscopy
the shape of the bacteria (rod/coccus)
size
grouping arrangements
shape of coccus
spherical
grouping arrangements
clusters or chains or single bacteria
what is shown from a MacConkey agar plate
lactose fermenter - red
lactose non-fermenter - yellow/colourless
purpose of blood agar plates
pathogens produce haemolysins - substances that destroy/lyse RBC in blood containing media - haemolysis
agar plates used to show the different types
alpha haemolysis
very small zone
colonies appear green
beta haemolysis
large clear zone haemolysis around the colonies
gamma haemolysis
no haemolysis
purpose of oxidase test
determine if organism produces cytochrome C oxidase
oxidase +ve bacteria are aerobic and use O2 as an electron receptor in respiration
test strip of oxidase test
contains tetra methyl-p-phenylenediamine (TMPD)
redox indicator - chemical that changes colour depending on the oxidation state of the molecule) and acts as artificial electron acceptor
colourless when reduced and dark blue/purple when oxidised
method for oxidase test
use strips
rub paper pad on the strips onto bacterial colonies on the agar plate
watch for colour change
catalase test
hydrogen peroxide toxic end product of aerobic breakdown of sugars
catalase break H2O2 into O2(g) and H2O
method for catalase test
pick loopful of bacteria and place with H2O2
bubbles = catalase +ve
coagulase test
check for presence of coagulase - clumping factor which reacts with fibrinogen = clots
used to distinguish different types of staphylococcus
method for coagulase test
shake test reagent from kit
add 1 drop test reagent to test circle
using plastic loop pick up bacterial colonies - mix with reagent in test circle
if there is clotting - bacteria are coagulase +ve
= staphylococcus aureus
