culturing of microorganism

culturing of microorganism Cultural techniques are used to isolate pathogens in pure cultures so that they can be identified. 1- the culture media used for growing microorganisms contains required nutreins in the correct amount, and PH (6.5-7.5) of the medium are also correct. 2- the microorganisms are incubated in an atmosphere (aerobic, anaerobic) and temperature (35-37C) most suited to their metabolism. 3- the culture media used for growing microorganisms should contain water and sources of nitrogen, carbon, menirals and essential vitamins.

Classification of culture media according to physical condition: a. solid medium: contain 2% agar. usually prepared in petridises b. semisolid media: contain 0.4% agar c. liquid medium: do not contain agar and prepared in tubes.

Phenomena of bacterial growth In liquid medium

On plate

Classification of culture media according to basic ingredients a. Minimal essential growth medium: such as nutreint agar and nutrient broth that will support the growth of M.O. that do not have special nutritional requirements. b. Enrichment medium: these are required for the growth of organisms special nutritional requirements such as H. influenza, Neisseria species, ex. Chocolate agar

Classification of culture media according to basic ingredients c. Selective medium: contain substances (antibiotics) which inhibits the growth of one organism to allow the growth of another to be growe clearly demonstrated. d. Differential medium: which contain dyes to differentiate microorganisms. They distinguish between bacteria by incorporating an indicator which changes color when acid is produced following fermentation of a specific carbohydrate. Many media used to isolate pathogens are both selective and enrichment or both selective and differential.

Differential Media Differentiates between different organisms growing on the same plate Example: Blood Agar Plates (TSA with 5% sheep blood) used to differentiate different types of Streptococci

Alpha Hemolytic Streptococci Incomplete lysis of RBC’s

Beta Hemolytic Streptococci Complete lysis of RBC’s

Gamma Hemolytic Streptococci No lysis of RBC’s

Selective and Differential Media Mannitol Salt Agar used to identify Staphylococcus aureus High salt conc. (7.5%) inhibits most bacteria sugar Mannitol pH Indicator (Turns Yellow when acid)

Selective and Differential Media MacConkey’s Agar used to identify Salmonella Bile salts and crystal violet (inhibits Gram (+) bacteria) lactose pH Indicator Many Gram (-) enteric non-pathogenic bacteria can ferment lactose, Salmonella can not

1. Obligate Aerobes

2. Obligate Anaerobes

3. Facultative Aerobes Facultative Anaerobes

4. Microaerophilic

Microaerophilic Bacteria A. Candle Jar 4 % CO2