 their students, today we will learn about different type of culture media for bacteria and their uses, preparation of nutrient broth medium and nutrient agar medium, microorganisms require nutrients and certain environmental conditions for their growth, culture medium provides all the nutrients required for the growth of microorganisms, a culture medium is basically an approach solution to which all the nutrients required for the growth of microorganisms have been added, culture media can be divided into different types based on consistency, composition and functional use and application, on the basis of consistency culture media pre-types, solid media, semi-solid media and liquid media, solid media in addition to all the nutrients required for the growth of microorganisms, it contains a solidifying agent, the most common solidifying agent is agar, it is added at a concentration of 1.5 to 2 percent, agar is a polysaccharide that is extracted from a seaweed, it is inert, it has no nutritional value, it solidifies at 42 degree centigrade and it liquefies at 98 degree centigrade, a solid medium has physical structure that allows the growth of bacteria in physically informative or useful ways in the form of flakes or colonies, solid media are used for the isolation of bacteria to study colonic characteristics and for the storage of bacterium, different types of solid media include nutrient agar medium, gloria, butenai, agar medium which is commonly known as lb agar and mccongee agar, in semi-solid medium in addition to the nutrients, the agar is added at a concentration of 0.2 to 0.5 percent, it has soft custard like consistency, it is used for the cultivation of micro-arrophilic bacteria and to study the motility of bacteria, examples of semi-solid media include mannitol motility test medium and semi-solid nutrient agar medium, liquid media are also known as broths, these media contain only nutrients and not traces of any solidifying agents like agar, in liquid media the bacteria grow uniformly producing turbidity, liquid media are used for the perfused growth of bacteria and in the fermentation studies, examples of liquid media include nutrient broth and lb broth medium, on the basis of composition, culture media are divided into two types, synthetic or chemically defined media and non-synthetic and chemically undefined media, chemically defined media are prepared from purified ingredients and their exact composition is known, example of chemically defined media include glucose salts agar, chemically undefined media contain at least one component that is not completely purified, characterized or is not consistent from batch to batch, such media often contain yeast extract, beef extract or enzymatic digestive proteins, examples of chemically undefined media include nutrient broth, nutrient agar and lb agar medium, dear students now we will study about different types of culture media based on functional use or application, we will study about basal media, enriched media, collective media and differential media, basal media are basically simple media that sports the growth of microorganisms that do not have any special nutritional needs, such media are used for the isolation of bacteria in lab and in sub-culturing processes, examples of basal media include nutrient broth medium, the composition of nutrient broth medium it contains peptone 1%, yeast extract 0.5% and NaCl 1%, the pH of nutrient broth medium is set to 7 for the growth of bacteria, peptone and yeast extract provide nitrogen compounds, amino acids, vitamins and other nutrients required for the growth of microorganism, while sodium chloride maintains the small concentration in the medium that is similar to the cytoplasm of the microorganism, second type is enriched media, enriched media are prepared by the addition of extra nutrients like serum, blood and egg yolk to the basal media, these media are used for the growth of mysterious microorganisms, examples of enriched media include blood agar and chocolate agar medium, blood agar is prepared by the addition of 5 to 10% sea blood to the blood agar base, while chocolate agar is laced or heated blood agar, selective media contain inhibitory substances that inhibit the growth of some bacteria while allowing the growth of other, selective media are agar base that are used to isolate different bacteria in labs, various approaches used to make the medium selective include the addition of antibiotics, dyes, chemicals, alteration of pH or a combination of these, differential media are also known as indicator media, differential media distinguish one microorganism from the other that are growing on the same plate, differential media contain indicators like dyes or metabolic substrates that give different colors to the colonies of different microbial species when they utilize or work with these compounds, macaunkey agar and minotaur salt agar are both selective as well as differential media, macaunkey agar selects program negative bacteria, it contain bile salts as well as crystal violet, these compound inhibit the growth of most of the gram positive bacteria, the peptone that is the pancreatic digest of gelatin and meat and calcium peptone, these provides the nitrogen sources, vitamins and other nutrients required for the growth of microorganism, sodium chloride maintains the osmotic balance, whereas lactose is the carbohydrate source in the medium and neutral red is the dye, some of the bacteria utilize lactose and these are known as lactose permenter, lactose permenter bacteria give red color colonies, red or pink colonies, while lactose nonpermenters give colorless colonies, when lactose permenter utilize the available lactose in the medium, they produce acid, the acid lowers the pH of the medium and the neutral red dye turns red, examples of lactose permenters include E. coli and C. capsiola species, whereas salmonella and shiella are lactose nonpermenters and they give colorless colonies, the second selective in differential media is mannitol salt agar, sodium chloride at a concentration of 7.5% selects for the members of the genus stryphylococcus, while this concentration is inhibitory to most of the other bacteria, the peptone and beef extract provide nitrogen compounds, vitamins and other nutrients required for the growth of microorganisms, mannitol is the carbohydrate source and phenol red is the dye, when bacteria ferment mannitol in the medium, they produce acid, the acidic byproduct decreases the pH of the medium and the phenol red turns yellow, so the mannitol fermenters give yellow colored colonies whereas nonpermenters give no color change, stryphylococcus aureus is when it all fermenter and it give yellow colored colonies whereas stryphylococcus epidermidis is a mannitol nonfermenter, now we will prepare 100 ml nutrient broth medium, post starting the preparation of the medium rinse all the glassware with distilled water, wear mask and gloves to avoid inhaling of the powder and to avoid prolonged skin contact, nutrient broth medium can be prepared either by adding individual components as we have discussed earlier or we can use premixed dehydrated media, in today's experiment we will use premixed nutrient broth medium, first of all check the lot number and the expiry of the medium, carefully read the directions given for the preparation of the medium, the pH of the premixed dehydrated media is adjusted by the manufacturer, so that after the medium is prepared the pH matches with that given on the label specification, for the preparation of 100 ml nutrient broth medium we will weigh 1.8 gram of nutrient broth powder, now I am going to wear mask before weighing the powder, place a small piece of paper on the weighing balance pan, press the tear key to zero out the weight of the paper, weigh 1.8 gram of nutrient broth medium, mixed dehydrated media are extremely hygroscopic, so immediately close the lid of the container after weighing, add 1.8 gram of nutrient broth medium to about 60 ml of distilled water, with the help of a cleansed glass stirrer, mix the powder, when the powder is completely dissolved, raise the volume up to 100 ml with distilled water, table of flask with the medium name and date, transfer the medium to the pre-labeled flask, cotton plug the flask, cover the flask with aluminum foil, 100 ml nutrient broth medium is prepared, for the preparation of 100 ml of nutrient agar medium, 2.3 gram of the nutrient agar powder has been added to 60 ml of distilled water, the volume has been raised to 100 ml, as the medium contain agar it needs to be heated and agar needs to be dissolved before autoclaving, heat the nutrient agar medium till boiling, nutrient agar medium is used for the preparation of nutrient agar flades and nutrient agar slants, for the preparation of the slants we will add about 7 to 8 ml of nutrient agar medium in each test tube, cotton plug the test tubes, cover the flask with aluminum foil, cover the flask of nutrient agar medium with cotton plug, cover the flask with aluminum foil, place the test tubes containing nutrient agar medium in a beaker, 100 ml of mannitol salt agar and macon ke agar have already been prepared according to the instructions given by the manufacturer, after the preparation of the media all media need to be sterilized, for sterilization place the media in an autoclave and sterilize at 121 degree centigrade 15 psi for 15 minutes, after autoclaving place the test tube in slanting position, keep the tubes in the slanting position till the medium solidify, after autoclaving pull the nutrient agar medium to about 50 degree centigrade, add about 15 to 20 ml of the medium in individual petri plates, always heat the mouth of the flask before pouring to avoid contamination, undisturbed till the medium solidifies, when it all salt agar and macon ke agar plates have already been prepared in the similar way, if the plates will be used later, seal the plates with parafilm at condensation of the moisture on the agar surface and place at 4 degree c till further use, turn nutrient agar slant in a zipper bag and keep at 4 degree c till further use,