Bacteria Lab Techniques Flashcards
What do liquid mediums look like/contain?
Straw coloured. Nutrients, containg meat infusions and Peptone (peptic enzymatic digestion of meat)
What is traditional name for liquid medium?
Broth
Solid medium is made from…
Liquid medium + Agar
What biological substance is commonly added to Solid medium?
Blood - which makes Blood Agar.
Would you inocculate a specimen onto MacConkey or Blood agar first? Why?
Blood Agar, because MacConkey may transfer over inhibitor.
What important properties do transport mediums have? (4)
Moisture, Neutral pH, Reducing environment, Stops diffusion of oxygen.
What is selective in MacConkey medium?
Contains bile salts, which some bacteria can survive in but others cannot.
Which bacteria can readily grow in MacConkey agar?
Bacteria normally in GIT.
What is the sugar in MacConkey’s medium?
Lactose
What colour would E.coli ferment on MacConkey’s agar? Why?
Pink/Magenta. The E.coli ferment lactose and produce acid - turning indicator (Neutral Red) pink.
What colour would non-lactose fermenters be on MacConkey’s agar?
Yellow
What is XLD?
A selective medium used to differentiate between E.coli and Salmonella. E coli are yellow, Salmonella show up black because of H2S.
What enzyme can used to be distinguish between Streptococcus and Staphylococcus?
Catalase - on hydrogen peroxide medium.
What is the FIRST step when identifying bacteria on a culture plate?
Gram stain.
What enzyme is used to distinguish pathogenic Staphylococci from non-pathogenic? Why use plasma not serum?
Coagulase. Plasma has to be used because it contains the clotting factors, serum doesn’t.
Why do you use one colony when testing for Antibacterial sensitivity?
So you don’t overwhelm antibiotics
What culture mediums are used for sensitivity tests?
Isosentitest or Diagnostic Sensitivity Test (DST) Medium
What is put onto sensitivity culture first: bacteria or antimicrobials?
Bacteria.
How can you tell if a bacteria is resistant to a antibacterial?
Zones of bacterial death around discs
What two enterobacteria can be found in faeces culture?
Campylobacter, Salmonella
If there are black colonies on XLD medium, why do you need to do a urease test?
Proteus also make black colonies, but are urease positive.
