Culture Media م.م رنا مشعل

Culture Media: is a medium (liquid or solid) that contains nutrients to grow bacteria in vitro. Because sometimes we cannot identify with microscopically examination directly, and we do culture for antibiotic sensitivity testing Note: media are sterilized by autoclaving at 121°C. With the autoclave, all bacteria, fungi, viruses, and spores are destroyed. Some media can’t be sterilized by autoclaving because contain eggs or carbohydrates. Properties of Media Support the growth of the bacteria. Should be nutritive (contains the required amount of nutrients). Suitable pH ,temperature and suitable atmosphere). (Bacteria grow at 370C).

There are three physical forms of media 1- Liquid, or broth media 2- Semisolid media 3-Solid media. The major difference among these media is that solid and semisolid media contain a solidifying agent (usually agar), whereas a liquid medium does not. Liquid media, such as nutrient broth, tryptic soy broth, or brain-heart infusion broth can be used to grow large numbers of microorganisms in fermentation studies and for various biochemical tests.

Liquid media is best when you want to rapidly increase the concentration of the organism or when you want to grow motile cells. The growth in liquid media: 1.Surface growth pellicle, 2.uniformly turbid, 3. Sediment in bottom

Semisolid media can also be used in fermentation studies, in determining bacterial motility and in promoting anaerobic growth.

Solid media such as nutrient agar or blood agar, are used (1) for the surface growth of microorganisms in order to observe colony appearance, (2) For pure culture isolations, (3) For storage of cultures, (4) To observe specific biochemical reactions

Culture media for bacterial growth Some bacterial species are able to grow under wide range of conditions , but others are very fastidious.

Types of Culture Media Simple culture media: are media that contain the basic nutrients (growth factors) that support the growth of bacteria without special nutrients, and they are used as basis of enriched media. E.g. Nutrient broth, nutrient agar, peptone water. They are for the growth of non-fastidious organisms like E.coli.

Enrichment media: Such as (blood agar, serum agar) are prepare to meet the nutritional equipment of more exacting bacteria by the addition of substance such as blood , serum , egg, to basal medium Selective media :: it is a mediam, which contains inhibitor substances that prevent the growth of microorganisms other than the bacteria for which the media is prepared for. For example: Mannitol salt Agar (MSA)

Differential Media it is a mediam, which contains a carbohydrate source and indicator to differentiate microorganisms based on their ability to ferment carbohydrate to produce acid end-products which react with the pH indicator and change its colore.g. MacConkey agar, which contains neutral red (pH indicator) and is used to differentiate lactose fermenter (E. coli )and non-lactose fermenter (Salmonella).the Organisms ferment lactose and produce acid end-products which react with the pH indicator neutral red, and produce a pink color. If the bacteria are non- lactose fermenter it will utilize protein source and produce alkaline products which react with pH indicator neutral red, and produce a pale yellow color.   .

nutrient agar,

Blood Agar - Chocolate Agar

Mannitol salt Agar (MSA) - MacConkey Agar

Type of organisms isolated media classification Selective agents Type of organisms isolated nutrient agar, simple basic nutrients E.coli. Chocolate agar enriched 1%hemoglobin Most fastidious pathogens such as neisseria and Haemophilus Blood agar Enriched and differntial 5%defibrinated sheep blood Almost all bacteria differntial for hemolytic organisms Maconkey agar Selective and differntial Lactose ,bile salt ,crystal violet Gram negative enteric bacilli