Culturing and Isolating Bacteria

Question 1

What is a mixed culture?

Answer 1

Holds 2 or more identified species/ strains of microorganisms

Question 2

What is a pure culture?

Answer 2

single species of bacteria

Question 3

What would you find in an isolated colony growing on an agar plate?

Answer 3

a visible mass of identical cells called a colony

Question 4

Steps you would take to obtain a pure culture from a mixed broth culture?

Answer 4

1. wipe area with hypochlorite (javex) solution 2. light bunsen burner 3. pick up test tube of mixed cultures in dominant hand and inoculating loop in other hand 4. pass the loop through the blue part of the flame and let cool for 10 seconds 5. remove the cap of test tube with the same hand the loop is in 6. pass the top of test tube through flame 7. insert loop into tube, avoiding the sides, flame test tube again and recap 8. remove lid of agar plate and streak back and forth on 1/3 of plate 9. reflame loop and let cool 10. turn plate 90 degrees and streak again streaking into the previous streaks for the first couple 11. reflame loop and let cool 12. turn 90 degrees and streak again streaking into the previous streaks 13. replace lid of agar plate and invert it, label bottom of plate 14. place plate upside down on rack to be incubated

Question 5

Importance of sterilization when preparing a pure culture?

Answer 5

to kill any remaining bacteria/microorganisms and reduce contamination

Question 6

Process of aseptic technique and importance of each step?

Answer 6

steps used to avoid contamination; it includes flaming the inoculating loop. see culture steps

Question 7

How is the three-phase pattern done on a streak plate and why is this technique useful?

Answer 7

1.streak back and forth on 1/3 of plate 2. reflame loop and let cool 3. turn plate 90 degrees and streak again streaking into the previous streaks for the first couple 4. reflame loop and let cool 5. turn 90 degrees and streak again streaking into the previous streaks useful because the organism is diluted over a solid surface

Question 8

What is a defined medium? provide example

Answer 8

culture solution in which all the components are known

Question 9

What is a complex medium? Example

Answer 9

culture solution in which not all molecules are known. can contain extracts of yeast, beef, blood, milk EX: nutrient broth and trypticase soy broth nutrient agar and trypticase soy agar

Question 10

What is a selective medium? Example

Answer 10

culture that prevents growth of some microbes while allowing the growth of others. EX: EMB (eosin methylene blue)

Question 11

What is a differential medium? Example

Answer 11

complex medium that contains additional substances that causes one group of organisms to show one kind of growth characteristic and another group a different characteristic. EX: blood agar

Question 12

Results of an alpha hemolytic bacteria grown on blood agar?

Answer 12

partially destroys RBC resulting in green or yellow zone around their colonies EX: streptococcus pneumoniae

Question 13

Results of a beta hemolytic bacteria grown on blood agar?

Answer 13

Destroys RBC, colonies are surrounded by a clear zone EX: streptococcus pyogenes

Question 14

Results of a gamma hemolytic bacteria grown on blood agar?

Answer 14

do not break down RBC leave the RBC and the medium as it is (no hemolysis occurs)

Question 15

Results of coliform grown on an EMB agar

Answer 15

selects gram-negavite bacteria to grow. ability to ferment. more quantity of acid present, the darker the colonies will be lactose. E.coli is an example

Question 16

Escherichia coli grown on EMB agar?

Answer 16

colonies are very dark and have a metallic green sheen to them

Question 17

Enterobacter aerogenes on EMB agar?

Answer 17

thick mucoid pink colonies. Dark centre surrounded by a wide light coloured rim having a “fish-eye” appearance