microbio practical 2 tests

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microbio practical 2 tests
2014-04-22 23:48:52
bio practical tests

microbio practical 2 tests
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  1. DMM medium
    • If there is a mutation in an amino
    • acid biosynthetic pathway gene, the bacteria cannot grow on DMM.
  2. TSA plate
    • TSA contains amino acids and can save a 
    • mutant via supplementation
  3. Plain LB plate
    contains no antibiotics
  4. Salmonella-Shigella (SS) Agar
    • Selective--- contains bile salts and brilliant green to inhibit Gram positive bacteria and most Gram negative bacilli
    • Differential---Lactose/ neutral red -
    • if ferment, form red colonies; not, colorless colonies
    • Sodium thiosulfate/ Ferric citrate -
    • colonies with black center are positive for H2S production
  5. MSA --- Mannitol salt agar
    • Selective for halophilic
    • bacteria--- staphylococcal spp.

    • Differential --- ferment mannitol à
    • eg. Staphylococcal aureus
    • do not ferment mannitol
    • eg. Staphylococcal epidermidis
  6. EMB--- Eosin Methylene Blue agar plates
    Selective--- Eosin and methylene blue inhibit the growth of Gram positive bacteria.

    • Differential--- lactose
    • fermentation (yes, pink; no, colorless
    • colonies) ---strong acid production
    • produces ‘greenish
    • metallic sheen’.
  7. Staphylococcus aureus
    • differentiated
    • from other Staphylococcal
    • skin flora based upon its ability of mannitol fermentation and
    • hemolysis.
  8. Blood agar medium
    used to detect (strongest to weakest) B, a, or y hemolysis
  9. Brain Heart Infusion plate:
    • BHI is a rich medium commonly used for the
    • isolation of fungi and bacteria
  10. staph catalase and coagulase
    • Catalase test---
    • Staphylococcal spp.
    • positive

    • Coagulase test ---
    • Staphylococcal aureus coagulase
    • positive
  11. Why is mannitol salt agar used as a selective medium for normal skin flora?
    • MSA selects for halophilic bacteria,
    • and salt resistant bacteria can be found on the skin’s surface
  12. Mitis-Salivarius Agar
    • Crystal violet---inhibit most G+ bacteria except streptococcus
    • Potassium tellurite---inhibit
    • G- bacilli
    • strep salivarius will produce gum-drops while strep mitis will make small,flat, light blue colonies
    • Enterococcus will make dark black blue colonies
  13. Is blood agar selective or differential? Explain
    • It is actually an enriched medium,
    • as most all bacterial species can grow upon blood agar. It could be considered
    • differential based upon hemolysin production, but it is not selective.
  14. What is one test that can be quickly used to differentiate between Staphylococci
    and Streptococci
  15. MacConkey Agar
    • used to isolate gram negative organisms, at the same time differentiate organisms
    • according to their lactose fermentation ability.
  16. Bile esculin agar
    commonly used to identify members of the genus Enterococcus (E faecalis and E. faecium).

    • ---Bile inhibits the growth of other Gram +
    • ---Sodium azide inhibits Gram –
    • ---Differentiates the ability to hydrolyze esculin

    many organisms hydrolyze esculin, but only Enterococcus spp. can do so in the presence of bile.
  17. urea broth inoculations
    • differential for urease production 
    • pink=positive
  18. Countable plate numbers
    • spread plates are countable if they fall between 25 – 250 isolated colonies. 
    • for the spot plate dilutions you would look for spots with at least 10 colonies and
    • no more than 30 colonies.