Microbiology practical 2

Question 1

Why do you use a selective and differential medium used?

Answer 1

• Selective media allow certain types of organisms to grow, and stops others
• Differential media are used to differentiate closely related organisms or groups of organisms

Question 2

What does catalyse test tell you?

Answer 2

Purpose of a catalyse test; tests for presence of catalase which breaks down tock peroxide to H2O and O2 it will bubble if there is catalase (+ve result)

Question 3

What is the purpose of a oxidase test? strong and weak +ve result -ve result

Answer 3

purpose of a oxidase test; used to id bacteria which produce cytochrome C oxidase which in an enzyme fo the ETC

+ve= aerobic (not strictly) and can use O2 as an electron acceptor in respiration

strong oxidase +ve organisms; colour change to deep blue purple within 10 seconds

weak +ve occurs within 10-60 seconds

-ve result= no colour change or bleached paper if the reagent has turned blue.

Question 4

What is the purpose of a spot indole test?

Answer 4

spot indole test purpose; to determine the presence of the enzyme troptophanase, which breaks down tryptophan to resale indole which reacts with cinnamaldehyde and produces a blue/green compound

-ve result there is no colour change

Question 5

What is the purpose of testing motility?

Answer 5

purpose of testing motility; to determine if the bacteria have a flagella present

+ve result; under the microscope the motile bacteria will dart across the view

-ve result; they don’t move

Question 6

Define haemolysis; Alpha and beta

Answer 6

Haemolysis; breakdown of RBC

Beta is the complete breakdown of RBC so there is a complete clear zone around the bacteria

Alpha; green zone of incomplete destruction of RBC around the bacteria

Question 7

What is the purpose of using a MacConkeys agar?

Answer 7

purpose of using a MacConkeys agar

• is both selective and differential
• if pink its lactase fermneting
• pale its non-lactose fermenting

Question 8

Which of the following is gram negative and gram positive?

Answer 8

Question 9

Dicuss the antibiotic susceptiblity

Answer 9

antibotic susceptiblity;

there is a zone of inhibtion (the area of clearing around it)

to determine if the ab worked you hvae to measure the ZOI and it must fall within the range which is acceptable if not than the disk has failed