Bacterial nutritional requirements. Composition of culture media. Categories of culture media. Solidifying agents. Types of media. Media Quality control.
1. Carbon Source: ◦ Heterotrphs: from organic compounds such as: a.a., polysaccharides, CHO, proteins and peptides. ◦ Autotrophs: from fixing inorganic carbon dioxide.2. Energy Source: ◦ Phototrophs: from sunlight. ◦ Chemotrophs: from oxidation of chemicals.3. Nitrogen: essential for a.a., nucleotide and vitamins synthesis.
1. Minerals: as cofactors in enzymatic reactions. ◦ E.g., sodium, potassium, calcium, magnesium, iron… etc.2. Growth factors: ◦ Amino acids, a.a.: bacteria possess proteinases. ◦ Purines and pyrimidines: to be converted to nucleotides. ◦ Bacterial vitamins: for co-enzyme production.3. Water: ◦ All metabolic functions of a bacterial cell are performed in aqueous environment. ◦ Distilled water Tap water minerals and their reaction with peptones and meat extracts.
1. Water.2. Peptone: product of protein hydrolysis. ◦ From animal proteins: source of nitrogen. ◦ From soya bean (plant) protein: source of carbohydrates, CHO.3. Meat extracts: as source of a.a. and other essential vitamins and elements.4. Yeast extract: as a stimulant for bacterial growth in the media.5. Mineral salts: for bacterial enzymes activity.6. Carbohydrates: as source of carbon and energy.
Chemically DefinedMedia Complex Media Is the one in which the Is the one in which the exact chemical exact chemical constitution of the composition is known. medium is not known. contain complex materials of biological origin such as blood or milk or yeast extract or beef extract, the exact chemical composition of which is obviously undetermined.
Agar: ◦ Is a complex polysaccharide (polymer of galactose) that is extracted from the cell wall of seaweed (red algae). ◦ It melts at 100oC and at 37oC it is solid. ◦ It has no nutritional value in agar cultures. ◦ It is added in a concentration of 1.5% to solidify media and 0.4% to make semisoft media. Gelatin: ◦ A protein which is derived from collagen of skin and bone. ◦ Some bacteria are able to liquefy gelatin at 37oC.
Consist of Without agar With agar In the form of Can be in the form ofPrimarily used for Primarily used for
In broths, bacterial growth is indicated by a change in the appearance from clear to turbid (cloudy). Turbidity of the broth is due to light deflected by bacteria present in the culture. The more turbid, the….
Basal Media: ◦ Simple media that will support the growth of most bacteria that do not require special nutrient. E.g., Nutrient broth. ◦ Nutrient broth+ agar= Nutrient agar Enriched media: ◦ Culture media that are enriched with whole or lysed blood, serum, special extracts or nutrient to support the growth of those bacteria that cannot grow on the basal media. ◦ Nutrient agar+ blood= Blood agar ◦ Blood agar+ heat= chocolate agar Selective media: ◦ Solid media which contain substances that inhibit the growth of some bacteria and letting the pathogenic ones grow.
Enrichment media: ◦ These are liquid media that are similar in function to ... ◦ The only difference is that… Differential media: ◦ Contains indicators that will differentiate one organism from another Transport media: ◦ Contain substances that can prevent overgrowth of commensals and prevent bacteria from dying as a result of change in pH or enzyme action.
Media should be tested for: 1. Sterility. 2. Each medium must be tested with organisms expected to grow or give a positive reaction as well as with organisms expected not to grow.
In a table, define each of the following media sugar, inhibitors, indicators and other additives: ◦ Bile Esculin Agar (BEA). ◦ Blood Agar. ◦ Chocolate Agar. ◦ Cysteine-tellurite Agar. ◦ MacConkey Agar. ◦ Mannitol Salt Agar. ◦ Salmonella-Shigella Agar. ◦ Selenite broth. ◦ Thayer-Martin Agar. ◦ Thiosulfate Citrate-bile salts (TCBS) Agar. ◦ Xylose lysine deoxycholate (XLD) agar.
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