To understand nutritional requirements of bacteria To study nutritional classification of bacteria To study constituents of nutrient media To understand types of nutrient media. To understand uses of different nutrient media

1. Nutritional requirements of
bacteria and nutrient media
Mrs. V. A. Warad
Assistant Professor
Pharmaceutical Microbiology
PES, Modern College of Pharmacy, (for Ladies), Moshi, Pune
S.Y.Bharm/Pharm.micro./2019 course/VAW
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2. Objectives
1. To understand nutritional requirements of bacteria
2. To study nutritional classification of bacteria
3. To study constituents of nutrient media
4. To understand types of nutrient media.
5. To understand uses of different nutrient media

3. Nutritional requirements of bacteria
Nutritional requirements of all living organisms are similar
1) Source of energy
Chemotrophs - oxidation of chemicals.
Ex. Nitrosomonas europaea - oxidation of ammoniun
ions
E. coli – oxidation of glucose
Phototrophs – energy obtained from light.
Ex. Rodospirillum rubrum
Chromatium okenii
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4. 2) Source of electrons
A. Lithotrophs - Electrons from reduced inorganic
compounds.
Chemolithotrophs – Nitrosomonas europaea
NH4+ + 3/2 O2 + H2O → NO2 + 2H2O + 2H + + e-
 Photolithotrophs - Chromatium okenii
H2S → S + 2H++ 2e-
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5. Source of electrons
Organotrophs - Electrons from reduced organic
compounds.
a. Chemo-organotrophs - E. coli
C6H12O6 + 6H2O→6CO2 + 24H+24 e-
b. Photo-organotrophs - Rodospirillum rubrum
Succinate → Fumarate + 2e- +2H+
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6. 3)Source of carbon
Autotrophs – Carbon dioxide
Nitrosomonas europaea
Chromatium okenii
Heterotrophs - organic compounds
E. coli
Rodospirillum rubrum
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7. Source of nitrogen
 Nitrogen gas – Azotobacter, Rhizobium
Inorganic nitrogen compounds – nitrates,
nitrites, ammonium salts.
Organic nitrogen compounds – amino acids,
proteins.
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8. Oxygen, sulfur, phosphorus
Oxygen – water, molecular oxygen, component
atom of various nutrients.
Sulfur – elemental sulfur, inorganic sulfur,
organic sulfur.
Needed for synthesis of cystine, cysteine,
methionine.
Phosphorus – supplied phosphates.
Needed for synthesis of nucleic acid,
phospholipids.
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9. Metal ions
Ca++, Mg++, K+, Fe++ required for normal
growth.
Trace elements – Zn++, Cu++, Mn ++, Ni++, Co++ ,
Mo6+, B3+
Occur as contaminants of other components.
Required in very small amounts.
Metal ions act as cofactors in enzyme reactions.
Most bacteria do not require Na+. Halophiles
require 12-15 % NaCl.
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10. Water
Bacteria are absorptive in mode of nutrients.
Nutrients must be present as aqueous solution
for absorption by bacteria.
It is polar solvent. It dissolves and disperse
cellular components.
It provides suitable environment for metabolic
reactions.
It is reactant in many metabolic reactions
It provides resistance to sudden and transient
temperature changes.
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11. Vitamins
Vitamins act as coenzymes in enzyme
reactions.
Most of the bacteria can synthesize their
vitamins .
Some bacteria can not synthesize their
vitamins and should be supplied in nutrient
medium.
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12. Nutrient medium
Def: Nutrient medium is defined as balanced
mixture of nutrients dissolved in water.
Nutrient media are used for cultivation of
microorganisms in laboratory.
Many nutrient media are used to facilitate
isolation, identification and enumeration of
bacteria.
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13. 1) Chemically defined media
Also known as synthetic media.
Pure chemicals.
Exact chemical composition is known.
Reproducible.
Costly.
Use – Cultivation of autotrophs.
Metabolic studies of heterotrophs
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14. 2) Complex media
Raw material – crude ingredients.
Exact composition is not known.
Not reproducible.
Cheaper.
Easy to prepare.
Contain ingredients like peptone, meat extract,
yeast extract, agar powder.
Use – cultivation of heterotrophs.
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15. Peptone
Prepared from proteins like meat, casein, gelatin.
 Proteins are partially digested by acids or enzymes.
Ex. Pancreatic digest of casein, soyabean digest
Use – Supply organic nitrogen. (C, N)
- May contain vitamins and carbohydrates
depending on kind of protein used.
- Can act as buffer
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16. Why peptone is used in nutrient
media and why not protein?

17. Meat extract / Beef extract
It is aqueous extract of lean beef tissue
concentrated to paste or powder.
Use – Contain water soluble substances like
carbohydrates, organic nitrogen, vitamins and
minerals.
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18. Yeast extract
It is aqueous extract of yeast cells available as
powder.
It is very rich source of B vitamins.
It also contains organic nitrogen and carbon
compounds.
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19. Agar as best solidifying agent
M.P. - 98⁰ c.
Gelling point – 450c.
Medium remains solid up to 900c. – it can be
used for cultivation of even thermophiles
It does not provide nutrients to bacteria and
does not change composition of medium.
It is not hydrolyzed by most of the bacteria.
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20. Agar powder
It is polymer of sulfuric acid ester of
D- galactose.
It is a polysaccharide obtained from sea
weeds like Pterocladia, Gelidium (brown
algae).
It is used as solidifying agent.
1.5 - 2 % agar - solid medium.
0.5 % agar – soft agar.
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21. 3) Enriched medium
It is rich in nutrients.
Additional nutrient sources like blood, serum,
plant or animal tissue extracts are added to
medium.
Ex. - blood agar, chocolate agar.
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22. Compare agar with gelatine as
solidifying agent.

23. 4) Enrichment medium
It is a liquid medium containing selective
agents.
It allows growth of specific organism and do not
allow growth of unwanted organisms.
It is used to increase relative proportion of
desired bacteria in mixed culture.
Ex – Selenite F broth, Terathionate broth for
Salmonella
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24. 5) Selective medium
It is a solid medium containing selective or
inhibitory agent.
It allows growth of desired microorganism and
does not allow or inhibit growth of unwanted
microorganism.
Ex. – Mac conkeys agar. – Intestinal bacteria
Mannitol salt agar.- S. aureus
Cellulose agar – cellulose degrading
bacteria
Cetrimide agar – P. aeruginosa
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25. What is difference between enrichment and
selective medium ?

26. 6) Differential medium
This medium helps to differentiate between two
groups of bacteria growing on it.
Ex. – Mac conkeys agar – differentiates between
lactose fermenting and lactose non- fermenting
between bacteria. Lactose and neutral red together
form indicator system
Blood agar - differentiates between α, β and γ
hemolytic bacteria.
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27. Colour of colonies of lactose fermeters and non-
lactose fermeters on Mac conkey’s agar
A- lactose
fermenting bacteria
B – Lactose non
fermenting bacteria

28. Question
 State whether True / False
Mac conkeys agar is a selective as well as
differential medium but Mac conkeys broth is
only selective but it is not differential medium.

29. 7) Indicator medium
This medium contains some chemical or indicator
which indicates growth of particular type of
bacteria.
Ex. – Wilson and Blaire medium. It contains ferrous
sulphate. Salmonella reduce sulphate to sulfide and
forms black sheen on colony.
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30. 8) Anaerobic medium
This medium is used for cultivation of
anaerobic bacteria.
It contains reducing agents.
Ex. – Robertsons cooked meat medium.
Fluid thioglycollate medium.
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31. 9) Assay medium
These media are used for microbial assay of
antibiotics and vitamins.
For every microbial assay specific standard
organism is used.
For every assay specific nutrient medium is
suggested in IP.
This medium supports maximum growth of
standard microorganism.
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32. 10) Media for enumeration of bacteria
It is used to determine total viable count of bacteria
present in natural soil, water, food sample.
It is more nutritive than simple nutrient agar and
supports growth of most of the bacteria present in
natural sample .
Ex. – Standard plate count medium.
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33. 11) Maintenance media
These are required to maintain viability and
physiological characteristics of culture.
They are not supposed to support rapid growth of
bacteria.
Rapid growth may results into rapid death of
bacteria.
Chemicals like glucose should be avoided in these
media.
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34. Transport medium
They are used for temporary storage of patient’s
sample being transported for cultivation to
laboratory.
It is used to prevent death of microorganisms during
transport and to maintain viability of all organisms in
specimen for sufficiently long period.
Contain mainly buffers and salt
Stuart medium – soft agar gel containing reducing
agents to prevent oxidation and charcoal to neutralize
- Nesseria gonorhoreae
Buffered glycerol medium – V. cholerae
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35. Minimal medium
Contain minimum nutrients for growth of
microorganisms.
They are devoid of growth factors - amino acids
and vitamins.
They are used to grow wild type of organisms
(prototrophic). Auxotrophic mutant organisms can
not grow on it.
Complete medium – contain growth factors
required for growth of auxotrophs
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