Culture Media and Microbial Growth Flashcards
How can media be classified?
Chemical composition, physical state, and functional type
How are chemical composition classified
Defined/Synthetic Media and Complex or Non-synthetic Media
Defined/Synthetic Media
Contains pure organic and inorganic compounds. Exact formula
Complex or Non-synthetic Media
One ingredient is not chemically definable. No exact formula
How is physical state classified?
Liquid Media, Semisold Media, and Solid Media
Liquid Media
Water-based solutions, typically broths, milk, and infusions. Used to measure turbidity
Semisold Media
Exhibits clot-like consistency at room temperature. Used to determine microbial motility and to localize a reaction at a specific site
Solid Media
Firm surface for discrete colony growth. Advantageous for isolation and pure culture.
How are functional types classified?
General purpose/supportive media, selective media, differential media, and enriched media
General Purpose/ Supportive Media
Supports wide range of microbial growth (ex. Nutrient broth/ agar)
Selective Media
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)
Differential Media
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)
Enriched Media
Supportive media with added nutrient. Used to encourage the growth of a particular microorganism in a mixed culture (ex. Blood agar)
What is Generation time
Time required for cell to divide/ for population to double
What is the average generation time for bacteria?
1-3 hours
What makes up the growth curve?
Lag Phase, Log Phase, Stationary Phase, and Death Phase
Lag Phase
Cells are recovering from a period of no growth and are making macromolecules and enzymes in preparation
Log Phase
(Exponential growth phase): Grows maximally
Stationary Phase
Occurs when nutrients are depleted and metabolic wastes accumulate
Death Phase
Death rate is greater than growth rate
How can you measure microbial growth?
Viable plate count, hemocytometer, flow cytometry, and spectrophotometer
