Microbial Culture Media: Types and Uses

• Culture media development has largely contributed to the field of microbiology.
• The discovery of these medias allowed for the development of microbiology in the nineteenth century, which facilitates studying the human microbiota through artificial mediums.
• Louis Pasteur cultured a bacterium in a reproducible way in 1860.
• This was made possible by the development of the first so-called artificial culture medium.
• Robert Koch furthered bacterial culture with the creation of the first solid culture medium, which allowed for bacterial colony production and purification.
• In 1860, Louis Pasteur developed a liquid culture medium that contained 'yeast soup', ashes, sugar, and ammonium salts.
• His goal was to show that each type of fermentation (alcoholic, acetic, lactic) was linked to a specific microorganism's development.
• The medium's components enabled observation of growth promotion or inhibition of specific bacteria, as well as the emergence of certain bacteria.
• In 1881, Robert Koch grew bacteria in a broth of fresh beef serum or meat extract.
• He then sought a method to solidify the medium, as the liquid culture failed to produce pure cultures.
• Initially, he experimented with coagulated egg albumin, starch paste, or aseptic potato slices.
• Gelatin was added to his broth, but it liquefied above 25°C and could be consumed by gelatinase.
• Fannie Hesse suggested using agar, which allowed for firm agars and bacterial isolation.
• In 1887, Julius Richard Petri created the Petri box.
• Culture media are gels or liquids containing nutrients used to grow and study microorganisms in laboratories.
• They are also known as growth media.
• Different cell types require varying types of media.
• Nutrient broths and agar plates represent the most common growth media.
• Certain microorganisms need specialized media to grow.
• Culturing on solid media offers a method to separate bacteria in a mixture.
• The significance is that culture media aids in identifying the causative agent behind infected material.
• This is followed by clinical diagnosis, studying the morphology and identification of the identified matter.
• In addition, culturing leads to obtaining antigens for vaccines.
• Culture use is also implemented in genetic manipulations of cells.
• Culture is used to:
  • Grow bacteria
  • Increase the number of existing bacteria
  • Select certain bacteria and suppress others
  • Differentiate between different kinds of bacteria
  • Essential to obtain a culture through growing an organism in an artificial medium

Media Components Requirements

• A minimum of nutrients are required to grow culture
• Water is essential for solubilizing nutrients, transporting them, and enabling hydrolysis reactions.
• Evaporation leads to smaller colonies and inhibits bacteria growth.
• Carbon is essential for bacteria, to produce fats, carbohydrates, proteins, and nucleic acids.
• Bacteria utilize inorganic carbon sources like carbon dioxide, or organic sources such as sugars and alcohols.
• Nitrogen sources are numerous and can come from various compounds and can be found in many mediums
• Nitrogen can be found in organic and inorganic formats, such as protein hydrolysates, or nitrates.
• Phosphates, sulfates, magnesium, and calcium are needed mineral salts.
• Energy source, phototrophic bacteria transform light into an electrochemical gradient.
• Energy source, chemotrophic bacteria oxidize mineral or organic compounds.
• Examples of bacteria energy sources are:
  • Thiocapsa roseopersicina
  • Listeria monocytogenes
• Growth factors are needed as minimal medium usage does not allow for the growth of certain bacteria that need specific elements to grow.
• Growth factors are added to increase the multiplication of bacteria
• Growth factors are elements bacteria cannot synthesize and the factors are justified by the absence or blocking of a metabolic pathway

Bacteria Growth Factors

• Arginine is needed in the growth of E.Coli
• Glutathione is needed in the growth of Gonococci
• Cholesterol is needed in the growth of Mycoplasma
• Aryl Sulphate Amide is needed in the growth of Atypical Mycobacteria
• Glycerol is needed in the growth of Mycoplasma Hominis
• Sulfonamides is needed in the growth of Rikettsia
• Tryptophan is needed in the growth of Salmonella Typhi
• L-Cysteine is needed in the growth of Listeria Monocytogens
• Sodium Chloride is needed in the growth of Vibrio Pararahemolyticus
• Factors X & V is needed in the growth of H.Influenzae
• Purine and pyrimidine bases are also used as growth factors and are necessary for the synthesis of Nucleic acids.
• Lactic acid bacteria needs adenine, guanine, thymine, or uracil for growth.
• Guanine is essential for growth of bacterium Leuconostoc mesenteroides,
• The common ingredients in media culture include the following
• Peptone: Source of carbon and nitrogen
• Beef extract: Source of amino acids, vitamins, and minerals
• Yeast extract: Source of vitamin, carbon, and nitrogen
• Distilled water: Solvent
• Agar: Solidifying agent

Culture Media Types

• Media cultures are classified based on physical states, presence of oxygen and nutritional factors.
• Broth(LY) or nutrient medium is the most popular.
• Agar is frequently used to solidify plates and allows for cultivation of bacteria.
• Liquid media allows bacteria to grow uniformly producing general turbidity and examples
• Diffused growth, inability to identify and difficult to isolate and early medium use urine or broth used by Louis Pasteur
• Solid media allows to easily identifying characteristics and macroscopically visible
• Solidifying agents: agar to create firm surface growth or isolate microorganisms is the function/use of
• Agar is an indispensable substance derived from red algae (Gelidium and Gracilaria species.
• Agar is composed of Agarose, Neutral Polymer, and Agaropectin(charged polymer)
• Agar is used in concentrations between 1-2% to solidify media which becomes solid at 40*C,
• Agar is chemically neutral and can allow visual of microbial colonies

Semi-Solid Media

• It is gel like which is achieved lower agent of .02-.0.5% and contains the following:
• The components are:
  • Nutrients
  • Indications
• The main components of Peptone are tryptophan, lysine, arginine, histidine, methionine, and phenylalanine, which can be used as a nitrogen fertilizer.
• Peptone: from Bovine, Porcine, gelatin and milk/yeast is digested protein created by enzymatic/acidic hydrolysis of proteinaceous materials
• Beef extract: Powder is a dehydrated extract of bovine tissue and used for culture media and examination of milk, water, and other materials as part of the uniform processes
• Aerobic (incubator-solid media)
• Anaerobic media consists of glucose, glycolate, ascorbic acid and cooked meat known as colostridium RCM
• Simple media- nutrient broth with peptone and meat
• Complex Media has components of amino acids, that can be chocolate ingredients and MacConkey
• Synthetic media has only pure ingredients and there is no yeast, plant or animal tissues and example is Dubo's media with Tween 80

Special Media

• Enrichment media- egg. blood or serum
• Selective media- to choose "selected" microoganism that prevents but makes easier to isolate , while preventing growth to favor vibrio Cholerae
• The inhibitory substance is added to solid media to prevent antibiotic, dyes, chemicals and alteration bacteria.
• Thayer Martin contains Vancomycin( gram positive, colistin and nystatin fungi and Proteu
• selective methylene inhibits dye and positive bacteria dyes.
• Campylobacter agar used characoal,Cefopeazone
• Differential media-peptone, agar and lactos and sodium taurocholate ingredients to identify various properties which can be the Mackonkey Agar type to differentiate microorganism

Examples of selective differential media

• MacConkey Agar
• Lactose negative pink
• Lactose positive color
• XLD agar is for Salmonella
• CLED agar is cultivation for urine and inhibit for protesu
• The enrichment of growth is also known as bacteria suppress for alkaline peptone and broth
• Transport media uses nonpathogeneic to buffer carb nutrients for transit to prevent transport. Stuarts medium- glycerolan saline
• Indicatory -blood allows microbioliogist to bacteria using enzymes that has PH indicators. With S.Typhi
• Sulphite media
• Sugar media uses any fermentibale . glucose, arabinose lactose, starch, Durham tubes with glucose.
• Bacteria contains1% which is glucose, mannitol, sucrose and transformed.

Culture Use

• Culture microbes •Identify Cause infection •to identify characteristics of microorganisms. •to isolate pure culture. •to store culture stock. •observe Reactions. •Test samples for contaminate •Check antimicrobial agents and preservatives effect. •Observe microbe colony cause,.shape. cause. •Differentiate between different colonies. •Create antigens for laboratory use. •Estimate viable count. •Test antibiotic sensitivity.

Limitations of culture media

• Limited shelf-life/temp control
• Bacteria enter dormant state that cant grow
• may inhibit organism
• Unwanted Atmosphere to many false positives
• High costs and lengthy process
• similar morphology and biohazards

Explore the uses of liquid and solid media in microbiology. This covers their advantages, the role of Durham's tubes; sugar concentrations in media; and visual indicators of bacterial growth.