Now, let us study culture media. We will first go over the physical forms of culture media, then the types of culture media. We will see in detail two examples, which are McConkey is auger and the mannitol salt auger. Finally, will study the cultural characteristics of colonies. In terms of physical form, media can be classified as liquid semi solid and solid. Examples of liquid is nutrient augur or lb auger, also known as nucleon brought in which case the media contains 2% auger semi solid media has only point 5% auger An example of semi solid media is the SI M which stands for sulfur indoor motility test used for testing the motility of bacteria containing phenol red dye in the media.

Shown here is an odd inoculated to have si AM. The media in the middle tube was inoculated with a loop containing Staphylococcus aureus specimen and the inoculation was done with a straight stab. The last tomb was inoculated with a specimen of protests will garris in a straight step. As one can notice that you with Staphylococcus aureus shows Red color only around the stab whereas the two bit protests will go with shows red color all over the media, indicating that protests will go is is more tile, while Staphylococcus aureus is not solid media, solid media contains one to one and a half percent auger example is blood auger used to test for hemolysis. That is the license of red blood cells, in this case by bacterial enzymes. This plate shows all three types of hemolysis alpha, beta and gamma.

Streptococcus pneumoniae causes a partial or incomplete hemolysis causing the media just underneath the bacterial colony to become greenish. This is called alpha hemolysis streptococcus pyogenes on the other hand, causes hemolysis underneath and around the colony and that's a complete hemolysis also known as Nita hemolysis. And crow caucus faecalis finally grows in blood sugar without causing any hemolysis and that is known as gamma hemolysis as shown here. Now, let us look at types of media. chemically defined media is the media in which the exact composition is known. It is used to grow kemo crops for crops and for microbiological This complex medium is the one in which the composition varies from batch to batch, it can be used for the growth of hetero graphic organisms.

Producing media is the one in which oxygen has been removed to allow for the growth of obligate anaerobes. Selective media is used for the suppression of unwanted microbes using salts, dyes or chemicals and thus, it encourages the growth of desired microbes. Differential media allow us to distinguish among different growing organisms. Finally, enriched media or enrichment media is designed to increase the number of desired microbes to detectable levels in a minute Next cultural situation. Next we will look at two types of media that are both selective as well as differential. First let us look at mK honkies other media McConkey is auger contains bile salts, crystal violet as well as neutral red dye, lactose and Pepitone.

The bile salts and the crystal violet inhibit the growth of gram positive bacteria. Now countless media is thus selective for the growth of gram negative bacteria. That is it allows for the growth of gram negative bacteria and suppresses the growth of gram positive bacteria. McConkey saga is differential for lactose fermentation Shown here is an on inoculated media of McConkey saga. Now eco ly enter back, klebsiella, salmonella Shigella, and DeSoto Mona's are all examples of gram negative bacteria. However, the first three ecola, Enterobacter and klebsiella are lactose fermenters.

Thus, the neutral red dye changes from colorless to red in low pH. Since lactose fermentation causes the media to become acidic. That's why you can see that the colonies for klebsiella are pink or reddish, whereas the Lastly species of salmonella Shigella and pisode homeowners do not ferment like lactose and so they do not cause a change in the media color. As shown here in the example of Shigella which remains brownish now, MSA MSA is short for mannitol salt, sugar. It contains seven and a half percent salt, a relatively high salt content that inhibits the growth of gram negative bacteria. It also contains a sugar mannitol and phenol red as the pH indicator.

MSA selective for the growth of gram positive bacteria mainly stuff like oxide and micro coxa. MSA is differential for mannitol fermentation does Staphylococcus aureus ferment mannitol and causes the pH of the media to become acidic and thus the phenol red changes the color of the media to a yellow color from the original and inoculated pink pinkish color, whereas staphylococcus epidermidis which is a non pathogenic bacteria does not ferment mannitol and thus the culture remains pink and does not change color. Now, let us look at cultural characteristics of colonists. The main characteristics are shape, margin, elevation, texture, surface appearance and pigment. Let us focus here on the first three. The colony shape is the form that is seen from the very top of the petri dish The shape can be circular, as shown here, irregular, funky form which means relatively small colonies filamentous and reside.

The colony margin or edge can be entire, on delayed or low bait. In terms of colony elevation we just seen from the plane of the petri dish, the colony can be flat raised Flat raised convex unburn eight or greater reform, which means similar to a crater. colony texture can be noticed usually when picked up with a loop and it can be moist mucoid dry or crusty. colony surface appearance can be opaque, translucent, shiny, or though some bacteria can produce a pigment. The pigment can then be classified as water soluble or water insoluble. Let us look at a few examples klebsiella pneumoniae colonies are mucoid in texture shiny in surface appearance, circular in shape convex in elevation and have an entire margin.

Bacillus saros on the other hand, are usually large in size, flat in elevation, double in appearance and underlaid in their margins, as noticed here. Bacillus saros we are mentioned now, Sarah Shia Marsh says sense this bacteria produces a red red pigment that is usually insoluble. The colonies are circular in shape and have an entire margin. Enterococcus faecalis, on the other hand, are generally very tiny and the spunky form convex in elevation. Have an entire margin. In summary, culture media can be liquid semi solid or solid in physical form.

There are several types of media of which the ones we mentioned as examples where the selective and the differential selective media allows for the growth of some and inhibits the growth of other micro organisms. Differential allows for the growth of two types due to unique characteristics for example, fermenters and non fermenters of sugars. McConkey zagar is selective for gram negative bacteria, and differential for lactose fermentation. MSA is selected for gram positive bacteria and differential for many tall form winters cultural characterization of colonies has to do with description of shape, margin, elevation, texture, surface appearance and pigment. This concludes the lecture on culture media.