9/12/2020

Nutritional requirements and raw materials used for culture media


Introduction:

  • Nutrition is substances used in biosynthesis and energy production and therefore are required for all living things.

  • Bacteria, like all living cells, require energy and nutrients to build proteins and structural membranes and drive biochemical processes.

  • Bacteria require sources of carbon, nitrogen, phosphorus, iron and a large number of other molecules.

  • Carbon, nitrogen, and water are used in the highest quantities.

  • The nutritional requirements for bacteria can be grouped according to the carbon source and the energy source.

  • Some types of bacteria must consume preformed organic molecules to obtain energy, while other bacteria can generate their own energy from inorganic sources.

Important Terminologies:

  1. CULTURE - the growth or crop of microorganisms obtained in a culture medium after its incubation period.

  2. CULTURE MEDIUM - any material where microorganisms may thrive for their nourishment and reproduction.

  3. INCUBATION PERIOD – is the time needed to let previously inoculated culture media to show a distinct colony or colonies within a desired temperature. 

    1. It is also the time needed for the microorganisms to adapt, grow and multiply in its new environment.

  4. COLONY - a group of microorganisms growing together characteristically in a culture medium.

  5. INOCULUM – the fished-out colony hanging on the wire loop, cotton swabs, etc. that is ready for transfer to another culture medium for cultivation and/or for further isolation.

Bacteriological Media:

  • Bacteriological media or culture media are an artificially prepared  mixture of various nutrients for the growth , multiplication, differentiation and transportation of microorganisms.

  •  A culture media must supply suitable  carbon,  nitrogen,  energy sources  and other nutrients.

  •  A lot of culture media are available but there is no single media suitable for growth of all microorganisms.

 Common ingredients used in bacteriological media :

  1. Water:

  •  Microbes  contain almost 70 to 80% water in their Protoplasm.

  • Water is used for preparation of culture media by dissolving various organic and inorganic compounds.

  •  Copper distilled water should not be used for preparation of culture media as copper is known to inhibit bacterial growth.

  1. Peptone:

  • Peptone Is a partially digested protein obtained from partial hydrolysis of  lean meat.

  • The important constituents of  peptone are  amino acids, proteases, certain inorganic salt and vitamins.

  •  Peptone acts as a nitrogen source and as a buffer.

  •  It must be stored in a tightly closed container as it is highly hygroscopic and becomes very sticky on contact with air. 

  1. Yeast Extract:

  • It is prepared from Baker's Yeast i.e. Saccharomyces

  • It contains carbohydrates, amino acids, inorganic salts and vitamins from the B complex group.

  • It is mainly used as a source of vitamins and can be substituted for  meat extract.

  1. Meat Extract:

  •  It is prepared by hot water extraction of fresh lean meat.

  • Contents are gelatin  peptones, proteases amino acids, mineral salt and certain vitamins.

  1. Agar:

  •   is long chain polysaccharide obtained from extraction of seaweeds called Agarophytes.

  •  Agar contains a mixture of two polysaccharides Agarose and Agaropectin  along with certain inorganic salts, a protein like substance and many inorganic ions.

  •  important properties of agar are as follows

    • Acts as a good solidifying agent (2%).

    • Has no nutritional value in the media.

    • Bacteriologically inert.

    • Resistant to the action of all microorganisms.

    • Stable at different temperatures used for incubation.

    • Melts @ 95 to 98 ℃ and remain liquid @ 40-45 ℃.

    • Gets solidified below 40℃ temp.

    • Economical and easily available.

Types of Culture Media:

  • They are classified in different way as follows;

  1. Depending on Physical State (Consistency):

    1. Solid Media (1.5 to 2.5 % Agar): e.g. Nutrient Agar.

    2. Semisolid Media (0.2 to 0.5 % Agar): e.g. Nutrient broth containing 0.5% Agar.

    3. Liquid Media (Absence of Agar): Fluid Thioglycollate broth.

  2. Depending on Oxygen Requirement:

    1. Aerobic Media: e.g. Mackonkey’s Broth.

    2. Anaerobic Media: e.g. Robertson’s Cooked Meat medium.

  3. Depending on Chemical Composition:

    1. Simple or Basal Media.

    2. Synthetic or Defined Media.

    3. Non-synthetic or Undefined or Complex Media.

  4. Special Media:

    1. Enriched Media.

    2. Enrichment Media.

    3. Selective Media.

    4. Indicator Media.

    5. Differential Media.

    6. Sugar Media.

    7. Transport Media.

    8. Assay Media.

    9. Storage Media.

Simple or Basal Media:

  • Basal media are basically simple media that supports most non-fastidious bacteria. 

  • Peptone-water, nutrient broth, and nutrient agar (NA) are considered as basal medium. 

  • These media are generally used for the primary isolation of microorganisms.

Synthetic or Defined Media:

  • These are prepared from pure chemicals and hence exact chemical composition is known.

  • Used for research purposes and to study metabolic activities of bacterias.

Non-synthetic or Undefined or Complex Media:

  • They contain complex chemical materials from biological origin whose exact composition is unknown.

  • These biological products provide growth nutrients required by bacteria.

  • These culture mediums may contain added nutritional materials.

Special Media:

  1. Enriched Media.

  • These media contain added nutritional substances for specific bacterias (Fastidious Bacterias).

  • E.g. Blood Agar (blood is added for streptococcus bacteria), Chocolate agar for Haemophilus sp., etc.

  1. Enrichment Media:

  • These mediums contain added substance that inhibit growth of unwanted bacteria and favors growth of a specific bateria.

  • It is a liquid medium.

  • E.g. Tetrathionate broth which inhibits growth of E. coli and favors growth of Salmonella sp. In feces.

  1. Selective Media:

  • It is just like enrichment media but is in solid form.

  • It also contains a substance that prevents growth of unwanted microbes and promotes growth of a specific microbe.

  • e.g. Lowenstein - Johnson medium for Mycobacterium tuberculosis which contain Penicillin, nalidixic acid and Malachite green that inhibit growth of other unwanted microbes.

  1. Indicator Media:

  • These media contain an indicator that changes color on growth of a specific microbe.

  • e.g. Wilson and Blair Media which contains sulphite, Salmonella typhi reduces this sulphite to sulphide in presence of glucose and produces colonic having black color with metallic shine.

  1. Differential Media:

  • A differential medium is used to distinguish colonies of different bacterias. 

  • e.g. MacCocnkey’s Agar which contains lactose, peptone, neutral red and differentiates lactose fermentation in red colored colonies from non lactose fermentation in pale or white colonies.

  1. Sugar Media:

  • In this 1% sugar is added to peptone water along with a suitable indicator.

  • Contains a small tube called Durham’s tube kept inverted for detection of production of gas by bacterias.

  1. Transport Media:

  • Clinical specimens must be transported to the laboratory immediately after collection to prevent overgrowth of contaminating organisms.

  • This can be achieved by using transport media. 

  • Such media prevent drying (desiccation) of a specimen, maintain the pathogen viable, and inhibit the overgrowth of unwanted bacteria

  • Some of these media (Stuart’s & Amie’s) are semi-solid in consistency. 

  • Addition of charcoal serves to neutralize inhibitory factors.

  • e.g. Cary Blair transport medium and Venkatraman Ramakrishnan (VR) medium are used to transport feces from suspected cholera patients.

  • e.g. Pike’s medium is used to transport streptococci from throat specimens.

  1. Assay Media:

  • These media are used for the assay of vitamins, amino acids, and antibiotics.

  • e.g. antibiotic assay media are used for determining antibiotic potency by the microbiological assay technique.

  1. Storage Media:

  • These help in preservation and storage of bacteria for a longer duration.

  • Dorset’s Egg Medium, Nutrient agar stabs, Robertsons cooked meat medium etc.

Labels: