Second year Lab Medicine (Females)1433- 1434 A.H. / 2012- 2013

Microbiology Practical (Course I)

Mrs. Hibah Abdul-Wahab I. Abu-Sulaiman

Who will be her groom??!

Royal Dining Royal Atmosphere

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.

4. Minerals: as cofactors in enzymatic reactions.◦ E.g., sodium, potassium, calcium, magnesium, iron…

etc.5. Growth factors:

◦ Amino acids, a.a.: bacteria possess proteinases.◦ Purines and pyrimidines: to be converted to

nucleotides.◦ Bacterial vitamins: for co-enzyme production.

6. 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.

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.

Without agar

With agar

In the form of Can be in the form of

Primarily used for Primarily used for

Consist of

Agar Slant Agar Deep Agar Plates

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:1. Bile Esculin Agar (BEA).2. Blood Agar.3. Chocolate Agar.4. Cysteine-tellurite Agar.5. MacConkey Agar.6. Mannitol Salt Agar.7. Salmonella-Shigella Agar.8. Selenite broth.9. Thayer-Martin Agar.10.Thiosulfate Citrate-bile salts (TCBS) Agar.11.Xylose lysine deoxycholate (XLD) agar.