Diagnostic microbiology course I

1. Second year Lab Medicine (Females)
1433- 1434 A.H. / 2010- 2011
Microbiology Practical (Course I)
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6.  Bacterial nutritional requirements.
 Composition of culture media.
 Categories of culture media.
 Solidifying agents.
 Types of media.
 Media Quality control.

7. 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.

8. 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.

9. 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.

10. Chemically Defined
Media 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.

11.  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.

12. Consist of
Without agar With agar
In the form of Can be in the form of
Primarily used for Primarily used for

13. Agar Slant Agar Deep Agar Plates

14.  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….

15.  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.

16.  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.

17.  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.

19.  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.