Micro

BONUS #5 (2 pts)

ANSWERS MUST BE TYPED

You are given a tube that contains a Gram + and a Gram – bacteria.

1. You must isolate them using selective media. You can choose 2 selective media.

 List them

MacConkey

CNA

 Explain why you chose those two

One will isolate the Gram – bacteria while the other will isolate the Gram + bacteria

2. Once isolated, I force you grow the colonies on a T-soy (because you should not do catalase off a CNA and you should not do oxidase off a MacConkey’s). Then I make you do an oxidase and a catalase test on each species. (normally you would not do oxidase on gram+ and you would not do catalase on gram -)

 Here are the results.

Catalase | Oxidase |

Gram + | Bubbled | No reaction |

Gram - | Bubbled | Turned purple |

a. BASED ON THE DATA: What is one type of aerotolerance the G+ might have? Defend your choice.

Facultative anaerobe, bubbling indicates the ability to break down H2O2 because it has the enzyme catalase which indicates the organism can perform aerobic respiration.

b. Is the Gram + Streptococcus or Staphylococcus? Defend your answer.

The Gram + is Staphylococcus. The catalase test is used to distinguish between Streptococcus and Staphylococcus, and since the result is positive (bubbling) it is Staphylococcus.

c. Using the G- identification chart in the lab manual, what species is the Gram – organism?

Pseudomonas aeruginosa

d. BASED ON THE DATA: What is one type of aerotolerance the G- might have? Defend your choice.

Obligate aerobe

The oxidase test is used to differentiate bacteria with the enzyme cytochrome oxidase (important to the electron transport chain which indicates ability to use aerobic respiration) from those that are missing it.