- It is nutritive ingredient needed by a particular m.o to enhance it growth under laboratory condition. -Different type of media: 1- Growth media(general media): most m.o can grow in this kind of media e.g. nutrient agar media, nutrient broth

2- Differential media: allows visual differentiation between two or more species of bacteria, e.g Macconkey agar, manitol salt agar *in these media some metabolic activity of an organism can be detected by observing the changes in the color of pH indicator.

e.g: Macconkey agar Manitol salt agar Staph.aureu (yellow) E.coli E.Coli staph.aureus (pink) (red) (yellow) Salmonella staph.epidermis Staph. Epidermis Bacillus (yellow) (yellow) (pink) (pink)

* Macconkey agar : - Because E.coli is lactose fermenter (it has the ability to ferment lactose) - Lactose is the indicator * Manitol salt agar: because Staph. aureus is manitol fermenter

3- Selective media: media that allow the growth of certain type of bacteria and prevent the other by using inhibitors(such as dyes,salt …..) e.g: * Macconkey agar (salt+crystal violet as inhibitor) -allow G-ve bacteria to grow - prevent G+ve bacteria

*Manitol salt agar(salt as inhibitor): -allow G-ve bacteria - inhibit G+ve bacteria(onlly Staph. aureus grow)

4- Enrichment media(blood agar): - it is a particular type of selective media - it will encourage the growth of particular type of microbes to increase their number to a point that they may be isolated in pure culture

5- Media for studying enzymatic activity : (starch agar): dark blue incubate iodin A B 37/24hrs A B clear zone

- Iodine work as indicator for the presence of starch - bacteria (A) produce alpha enzyme that break starch macromolecule to micromolecule,this is called starch hydrolysis

1- Catalase test: To determine the ability of some m.o to degrade hydrogen peroxide by enzyme catalase. *Aerobic bacteria produce enzyme catalase that convert toxic hydrogen peroxide (produce in the cell) to water and oxygen.

2H 2 O 2 Enzyme catalase 2H 2 O+O 2( release of O 2 gas as air bubble -the stronger the reaction the more air bubbles. -the weaker the reaction the less air bubbles. *Streptococcus+H 2 O 2 no bubbles(catalase -ve) *Staphylococcus+H 2 O 2 air bubbles(catalase +ve)

2- Starch hydrolysis: Purpose : to determine that bacteria produce enzyme amylase that break down starch macromolecule to glucose(micromolecule). - The presence of starch can be indicated by the blue color(when we add iodine to the starch media).

3- API test: It is a test for identification of bacteria - it is a rapid test (because it has different test in one stip of test). *different test such as: 1- amino acid test(arganin,lysin … ) 2- carbohydrate test(sugar test) 3- hydrogen sulfide production

- We can identify the genus as well as species by using this test, but most biochemical test we can identify only genus. e.g: Bacillus subtillus (genus) (species)

- It is plastic strip holding 20 mini tube inculated with a saline suspension of pure culture. *some tubes are over laid with mineral oil for the anaerobic reaction.

-for the sugar test: yellow red ( sugar ferment (-ve test) to acid)