Microbiology Lab Review: Chapter 9

Chapter 9 - Colony Morphology

1.    [CH-09-01] Compare the appearance of bacterial and fungal colonies. What accounts for the difference?

Bacteria = small and compact colonies. VS Fungus = large and flurry colonies.

Fungus has long fibers called hyphae that expand to extract nutrients from the surroundings. The hyphae also extend to form spores to spread the fungus. à Gives the fungus a fuzzy look.

2.    [CH-09-02] Can you think of any solidifying agent other than agar that might be suitable for the growth of bacteria?

Gelatin – Animal source protein that

Starch – Polysaccharide (polymer of glucose)

Both can be used as differential mediums.

3.    [CH-09-03] What is the advantage of growing bacteria on solid media? –

Bacteria growing on solid medium form colonies that can be used to allow for creation and maintenance of pure cultures.

4.    [CH-09-04] Describe bacterial morphology, oxygen and temperature requirements of Bacillus subtilis – Rod shape, single cells, facultative aerobes, mesophiles (25-35ºC)

5.    [CH-09-05] Describe bacterial morphology, oxygen and temperature requirements of Staphylococcus epidermidis – Staphylococci (circular cells arranged in grape like arrangement), facultative anaerobe, mesophile

6.    [CH-09-06] Colony size, color, and shape are critical of bacterial growth description. At least three other crucial factors – not description of the organism itself – typically included when describing bacterial growth. What are they and why are they important?

Oxygen requirements → Determine bacteria’s oxygen requirements in the environment important when trying to culture the bacterial colonies.

Optimal temperatures → Determines bacteria’s growth temperature range (Optimal temperature for rapid growth).

Tonicity → Bacterial growth environment for solutes.

7.    [CH-09-07] What steps should be taken before attempting to light Bunsen burner?

Make sure that the gas supply line is secure. Check to see that the gas control valve is closed. Ensure that the air vent is closed to prevent gas from leaking sideways (can adjust later).

8.    [CH-09-08] If the flame is yellow what does this indicate? What adjustments must be made?

Not enough oxygen during combustion, need to open vent more to allow more air into the Bunsen burner.

9.    [CH-09-09] Suppose you cough on plate and there is no growth after incubation. It is highly unlikely your cough was sterile. Suggest at least two reasons why no growth was recovered on the plate.

Temperature of plate during incubation was unsuitable for growth.

Culture media did not provide enough growth factors for bacteria.

10. [CH-09-10] If you found the colony to be a mixture of organisms, what could you do to isolate them as pure cultures?
Place the sample from the colony with a mixture of organisms into a liquid broth and dilute the sample to a more manageable amount. Then make a new steak plate using a sample from the liquid broth.