Microbiology- bacteria Flashcards
What colour do gram negative bacteria appear under the microscope?
pink
What colour do gram positive bacteria appear under the microscope?
purple
Describe blood agar
contains sheeps/horse blood
Describe chocolate agar
Contains blood agar heated to 80 degrees c for 5 minutes. This releases some of the nutrients into the agar to make it easier to grow certain organisms that do not grow easily.
What does CLED agar stand for?
cysteine lactose electrolyte deficient
What colour is a lactose fermenting gram negative bacilli on CLED agar?
yellow
What colour is non-lactose fermenting gram negative bacilli on CLED agar?
blue
What type of bacteria is MacConkey agar primarily designed to grow?
gram negative bacilli
What does MacConkey agar contain that inhibits gram positive bacteria?
bile salts
Does MacConkey agar contain lactose?
yes
What colour are lactose fermenters on MacConkey agar?
pink
What colour are non-lactose fermenters on MacConkey agar?
yellow/colourless
What type of agar would you use to grow Neisseria spp. ?
gonococcus agar
What type of agar would you use to isolate salmonella spp. or shigella spp. ?
XLD agar
How do colonies of salmonella and shigella look on XLD agar?
salmonella- red with black centres
shigella- red
What type of agar is used to culture fungi?
Sabouraud’s agar
Which genus of bacteria is gram positive cocci and arranged in clusters?
Staphylococcus
What genus of gram positive cocci is found in chains?
Streptococcus
For what genus of gram positive cocci would you carry out haemolysis on blood agar to classify further?
Streptococcus
Describe the arrangement of Staphylococcus
clusters
Describe the arrangement of Streptococcus
chains
How are beta haemolytic strep further classified?
by antigenic group
Are viridan’s strep alpha or beta haemolytic?
alpha
What type of alpha haemolytic strep is sensitive to the optochin test?
S. pneumoniae
Which Staphylococcal species will produce a positive coagulase test?
S. aureus
Describe the disease causing potential of Staphylococcus aureus compared to Staphylococcus epidermidis ?
Disease causing potential of S. aureus is high
Disease causing potential of S. epidermidis is low
What colour are S. aureus colonies on blood agar ?
gold (aureus is latin for gold)
Which out of S. aureus and S. epidermidis displays coagulase activity?
S. aureus
Describe the colonies of S. epidermidis
White/not pigemented
coagulase-negative staphylococci are a common cause of what infection?
line infection
What does a positive coagulase test look like?
clot formation in test tube
Describe what beta haemolysis looks like on blood agar
clearing of agar round colonies
describe what alpha haemolysis looks like on blood agar?
greening of agar round colonies
How do you test alpha haemolytic strep for S.pneumoniae?
optochin test
What can Streptococcus pneumoniae cause?
lobar pneumoniae and meningitis
What further grouping can we do to beta haemolytic streptococci?
Lancefield grouping
What antigen do enterococci have?
D
What antigens on beta haemolytic streptococci can cause skin infection and tonsilitis?
A, C and G
What can beta haemolytic strep with B antigen cause?
neonatal sepsis and meningitis
What type of haemolysis is it when there is a clear zone around colonies?
beta
