Tiêu đề 6. STUDY OF DIFFERENT IMPORTANT MEDIA REQUIRED FOR THE GROWTH OF AEROBIC AND ANAEROBIC BACTERIA & FUNGI. DIFFERENTIAL MEDIA, ENRICHED MEDIA AND SELECTIVE MEDIA.pdf ✅

PHARMD GURU Page 1 BACTERIOLOGICAL MEDIA: Media are an artificially prepared mixture of various nutrients for the growth and multiplication of microorganisms (singular-medium). A wide variety of culture media is employed by the microbiologist for the isolation, growth, purification, maintenance and identification of microorganisms. A culture media must supply suitable carbon, nitrogen, energy sources and other nutrients. Nutrient agar is a common laboratory medium (Table 3.2) used for growth of many bacterial species. It is important to note that not a single medium is suitable for growth of all microorganisms. COMMON INGREDIENTS OF MEDIA: 1. Water: Tap, pure or distilled water may be used for the preparation of culture media by dissolving various organic and inorganic compounds. In the protoplasm of a cell, 70 to 80% water is present and it acts as a vehicle for the flow of nutrients. All enzymatically controlled chemical reactions occur within the cell in the presence of water. Copper-distilled water cannot be used for preparation of media because copper inhibits bacterial growth. STUDY OF DIFFERENT IMPORTANT MEDIA REQUIRED FOR THE GROWTH OF AEROBIC AND ANAEROBIC BACTERIA & FUNGI. DIFFERENTIAL MEDIA, ENRICHED MEDIA AND SELECTIVE MEDIA
PHARMD GURU Page 2 2. Peptone: It is a complex mixture of partially digested proteins obtained from lean meat, heart muscle, casein, fibrin, soya meal etc. The important constituents are proteases, amino acids, inorganic salts which include phosphates, potassium and magnesium and growth factors including nicotinic acid and riboflavin. Peptones mainly supply nitrogenous material and also act as a buffer. Peptone is stored in a tightly closed container because it is hygroscopic and becomes sticky when exposed to air. 3. Yeast extract: Yeast extract is prepared from cells of baker's yeast or Saccharomyces. It contains carbohydrates, amino acids, growth factors (vitamin B group) and inorganic salts. Yeast extract is used mainly as a source of vitamins and may be substituted for meat extract. 4. Meat extract: Meat extract is prepared from fresh lean meat by hot water extraction process. It contains gelatin, peptones, proteases, amino acids, creatine, creatinine, purines, mineral salts, carbohydrates and growth factors includes thiamine, nicotinic acid, riboflavin, pyridoxine and pantothenic acid. 5. Agar: Agar is a long chain polysaccharide obtained from seaweeds algae (class: Rhodophyta). These algae which yield agar are called Agarophytes that includes: Gelidium, Gracilaria, Hyphea, Gelidiella, Ceramium etc. Agar is a mixture of two polysaccharides such as aggarose (70%) and agaropectin (30%). It also contains calcium, chloride, magnesium, sulphate, iron etc. Agar or agar-agar is now commonly used for the preparation of solid media. Properties of agar are as follows:  Prepared from different seaweeds algae.  It acts as good solidifying agent (2%).  It has no nutritional value in media.  Bacteriologically inert.  Resistant to the action of all microorganisms.  It is stable or firm at different temperatures used for incubation.  It melts at 95 to 98oC and remains liquid upto 40 to 42oC.  It gets solidified below 40oC.  Easily available and economical. TYPES OF CULTURE MEDIA: Culture media may be classified in different ways:
PHARMD GURU Page 3 (A) Depending on physical state (media consistency):  Solid media (1.5 to 2.5% agar) e.g. Nutrient agar.  Semisolid media (0.2 to 0.5% agar) e.g. Nutrient broth containing 0.5% agar.  Liquid media (absence of agar) e.g. Fluid thioglycollate broth. (B) Depending on oxygen requirement:  Aerobic media e.g. MacConkey's broth.  Anaerobic media e.g. Robertson's cooked meat medium. (C) Depending on chemical composition:  Simple or basal media.  Synthetic or defined media.  Non-synthetic or undefined or complex media. (D) Depending on functional type:  Enriched media  Enrichment media  Selective media  Indicator media  Differential media  Sugar media  Transport media  Assay media  Storage media  Simple or basal media: These media includes peptone water and nutrient broths which form the basis of most media used in the study of common bacteria. Addition of 2% agar to nutrient broth forms a nutrient agar medium which is a solid basal medium.  Complex or non-synthetic or undefined media: Complex media usually contains complex materials of biological origin such as blood or milk or yeast extract or beef extract. The exact chemical composition of this media is not known but it provides all the growth factors for the cultivation of unknown bacteria. These media may be added ingredients for special purposes for growth of specific microorganisms.
PHARMD GURU Page 4  Synthetic or defined media: These media are prepared from pure chemical substances and the exact composition of the medium is known. These media are used for research purposes as well as metabolic studies of different microorganisms. Special media: List of different type of media commonly used for isolation of bacteria are given in Table 3.3 1) Enriched media: These enriched media are prepared for fastidious microorganisms by addition of substances such as blood, serum and egg to basal medium. e.g. blood agar (Streptococcus), chocolate agar (Neisseria, Haemophilus), Loeffler's serum slope (Corynebacterium diphtheriae). 2) Enrichment media: When a specific substance is added in a liquid medium which inhibits the growth of unwanted bacteria and favours the growth of wanted bacteria, such a media is called as enrichment media e.g. tetrathionate broth, selenite F broth. These media inhibits coliforms (e.g. Escherichia coli) by allowing growth of pathogenic cultures (e.g. Salmonella species, Shigella species) from feces. 3) Selective media: This is like enrichment media but is in a solid form. When a substance is added to a solid medium which inhibits the growth of unwanted