Lab 6 Culture media Medium is an environmental

Lab 6 Culture media Medium is an environmental mixture of essential required nutrients for surviving and growing of microorganisms that contains: C, N, P, S and elements such as Fe, Cu, Ca, Zn, Mg, Mo, Cl- and vitamins , growth factors. There are several types of media, which are classified due to their physical forms or due to the purpose of using. Physical forms of media: Liquid media: Nutrient broth, mineral salt broth, brain heart infusion broth, tryptic soy broth etc.

Types of culture media due to the purpose of using A- Selective media: Some of the media are contained stains or antibiotics (inhibitors) which prevent growth of some microbial groups and allow other groups, to grow; these specific media are termed selective. These types of media are used for Mac. Conkey agar and broth. For enteric bacteria. These media are used for isolation the enteric or coliform bacteria , which contains bile salts and crystal violet, that inhibits all bacterial growth except the coliform or enteric bacteria , their appears in red colour on the Mac. Conkey agar. Compositions of Mac. Conkey agar.

Figure (13) - Mac. Conky agar – L. F. and N. L. F

EMB- Agar EMB is the selective and differential medium for coliforms. It contains the following ingredients: peptone, Lactose, Dipotassium phosphate, Eosin Y (dye), Methylene blue (dye) and Agar. This medium inhibits the growth of Gram-positive bacteria and provides a color indictor; if E. coli is grown it will give a distinctive metallic green sheen with a dark center, Aerobacter aerogenescolonies have a brown center, and nonlactose-fermenting gram-negative bacteria appear pink.

Mannitol salt Agar (PH 7. 4): This medium is used for isolation of pathogenic Staphylococcus (S. aureus) , which contains high concentrates of Na. Cl (7 -10%), that inhibits the groth of nonpathogenic staphylococci and other types of bacteria. The colonies of S. aureus change to yellow and colour of culture medium change from pinck to yellow due to the formentatior of mannitol sugar. Compositions Figure (14)- Mannitol Salt Agar

Selective media (for fungi. Molds and yeast). There are several media , that can be used for isolation of the fungi , these media has specific materials as carbon sources, which can be utilized by the fungi or by adding antibiotics or stains , that inhibits or kills the bacteria , such as the following media. Sobouraud Dextrose Agar (PH 5. 6) for molds and yeast. Peptone 10. 0 gm Dextrose 40. 0 gm Agar 15. 0 gm Dist. water 1. 0 L Potato Dextrose Agar. (PH 5. 6) Potatoes infusion 100. 0 gm Rose bengal Agar. (PH 4 -6)for molds Malt extract 30. 0 gm Rose bengal stain 0. 006 gm Streptomycin sulfate 0. 003 gm Agar 20. 0 gm Tape water

B- Enriched Media Most of the oral bacteria isolated on enriched media such as brain heart infusion agar or broth, blood agar, and tryptic soy agar or broth. Brain – Heart Infusion Agar (PH 7. 4)

Figure (15) - a- β- hemolytic, b- α- hemolytic

Preparation of Chocolate Agar Add 5% sterile defibrinated blood to the blood agar base. Heat at 80 ºC until chocolate color develops C- Differential media (specific media). Differential media are contained an indicators, their colour changes due the activity (ies) of the microorganism such (oxidation or fermentation of the specific carbohydrates or other c-sources which presents in the medium. Example of such media: 1 - Eosin – Methylene Blue (EMB) PH 7. 2. 2 - Mac. Conky- Agar or Broth –Differentiation between L-F & N. L. F. 3 - Sugar Broth – Differentiation between sugar fermenter and nonfermenter. 4 - Blood Agar – Differentiation between hemolytic and nonhemolytic