6. Bacterial nutritional requirements.
Composition of culture media.
Categories of culture media.
Solidifying agents.
Types of media.
Media Quality control.
Culturing techniques.
Condition of incubation.
7. 1. Carbon Source:
◦ Heterotrphs: from organic compounds such as: a.a.,
polysaccharides, CHO, proteins and peptides.
◦ Autotrophs: from fixing inorganic carbon dioxide.
1. Energy Source:
◦ Phototrophs: from sunlight.
◦ Chemotrophs: from oxidation of chemicals.
1. Nitrogen: essential for a.a., nucleotide and
vitamins synthesis.
8. 4. Minerals: as cofactors in enzymatic reactions.
◦ E.g., sodium, potassium, calcium, magnesium, iron… etc.
4. Growth factors:
◦ Amino acids, a.a.: bacteria possess proteinases.
◦ Purines and pyrimidines: to be converted to nucleotides.
◦ Bacterial vitamins: for co-enzyme production.
4. 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.
1. Meat extracts: as source of a.a. and other essential
vitamins and elements.
2. Yeast extract: as a stimulant for bacterial growth in
the media.
3. Mineral salts: for bacterial enzymes activity.
4. Carbohydrates: as source of carbon and energy.
10. Agar:
◦ Is a complex polysaccharide (polymer of galactose) that
is extracted from the cell wall of seaweed (red algae).
◦ It has no nutritional value in agar cultures.
Gelatin:
◦ A protein which is derived from collagen of skin and
bone.
◦ It has no nutritional value in agar cultures.
13. In broths, bacterial growth is indicated by a
change in the appearance from clear to turbid
(cloudy).
The more turbid, the….
14. 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 others grow.
15. 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.
16. 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.
17.
18. But when we’ll go over it, it’ll
The media looks like this… look like this ;)
25. Too high temperature will denature bacterial
ezymes. While too low temperature….
Types of bacteria according to their growth
temperature:
1. Psychrophiles: bacteria that grow between 0-20oC.
2. Mesophiles: those that grow between 21oC and 50oC.
3. Thermophiles: the ones that grow between 50oC and
100oC.
26. Acidophiles: bacteria that grow in acidic pH.
Neutrophiles: those that grow in between 4-9.
Alkalophiles: ones that grow in alkaline pH.
27. Bacteria differ in their need to molecular oxygen for
growth:
Obligatory (strict)aerobes: require free oxygen for
growth.
Obligatory (strict) anaerobes: grow only in the
absence of free oxygen.
Facultative anaerobes: multiply either in the
presence or absence of free oxygen.
Carboxyphilic (capnophilic): these bacteria require
raised level of carbon dioxide (5-10%).
