Culture Media and Microbial Growth

Question 1

How can media be classified?

Answer 1

Chemical composition, physical state, and functional type

Question 2

How are chemical composition classified

Answer 2

Defined/Synthetic Media and Complex or Non-synthetic Media

Question 3

Defined/Synthetic Media

Answer 3

Contains pure organic and inorganic compounds. Exact formula

Question 4

Complex or Non-synthetic Media

Answer 4

One ingredient is not chemically definable. No exact formula

Question 5

How is physical state classified?

Answer 5

Liquid Media, Semisold Media, and Solid Media

Question 6

Liquid Media

Answer 6

Water-based solutions, typically broths, milk, and infusions. Used to measure turbidity

Question 7

Semisold Media

Answer 7

Exhibits clot-like consistency at room temperature. Used to determine microbial motility and to localize a reaction at a specific site

Question 8

Solid Media

Answer 8

Firm surface for discrete colony growth. Advantageous for isolation and pure culture.

Question 9

How are functional types classified?

Answer 9

General purpose/supportive media, selective media, differential media, and enriched media

Question 10

General Purpose/ Supportive Media

Answer 10

Supports wide range of microbial growth (ex. Nutrient broth/ agar)

Question 11

Selective Media

Answer 11

Contains compounds that selectively inhibit growth of a certain microbe but encourages, or selects, a specific microbe (ex. Mannitol Salt Agar, had 7.5% NaCl which inhibits the growth of gram + bacteria but encourages the growth of staphylococcus aureus)

Question 12

Differential Media

Answer 12

Differentiates among various groups of microbes, colony size or color, changes in media color, formation of gas bubbles and precipitates (ex. Blood agar for hemolysis)

Question 13

Enriched Media

Answer 13

Supportive media with added nutrient. Used to encourage the growth of a particular microorganism in a mixed culture (ex. Blood agar)

Question 14

What is Generation time

Answer 14

Time required for cell to divide/ for population to double

Question 15

What is the average generation time for bacteria?

Answer 15

1-3 hours

Question 16

What makes up the growth curve?

Answer 16

Lag Phase, Log Phase, Stationary Phase, and Death Phase

Question 17

Lag Phase

Answer 17

Cells are recovering from a period of no growth and are making macromolecules and enzymes in preparation

Question 18

Log Phase

Answer 18

(Exponential growth phase): Grows maximally

Question 19

Stationary Phase

Answer 19

Occurs when nutrients are depleted and metabolic wastes accumulate

Question 20

Death Phase

Answer 20

Death rate is greater than growth rate

Question 21

How can you measure microbial growth?

Answer 21

Viable plate count, hemocytometer, flow cytometry, and spectrophotometer