Immune System, part 1: Crash Course A&P #45

Our final episodes of Anatomy & Physiology explore the way your body keeps all that complex, intricate stuff alive and healthy -- your immune system. The immune system’s responses begin with physical barriers like skin and mucous membranes, and when they’re not enough, there are phagocytes -- the neutrophils and macrophages. It also features the awesomely named natural killer cells and the inflammatory response, and we'll explain how all of these elements work together to save the day if you happen to slip on a banana peel.

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Mueller Hinton Agar

Mueller Hinton Agar (MHA) The major use of Mueller Hinton Agar is for antimicrobial susceptibility testing. Composition of MHA Ingredients Beef Extract 2.00 gm Acid Hydrolysate of Casein 17.50 gm Starch 1.50 gm Agar 17.00 gm Distilled Water 1000 ml Final pH 7.3 ± 0.1 at 25ºC Why Mueller Hinton agar is used for antibiotic susceptibility testing? 1. It is a non-selective, non-differential medium. This means that almost all organisms plated on here will grow. 2. It contains starch. Starch is known to absorb toxins released from bacteria, so that they cannot interfere with the antibiotics . It also mediates the rate of diffusion of the antibiotics through the agar. 3. It is a loose agar. This allows for better diffusion of the antibiotics than most other plates. A bette

Simmons Citrate Test

Simmons Citrate Reaction It used to differentiate among the Gram-Negative bacilli in the family Enterobacteriaceae. Principle Citrate agar is used to test an organism’s ability to utilize citrate as a source of energy. The medium contains citrate as the sole carbon source and inorganic ammonium salts (NH4H2PO4) as the sole source of nitrogen . Bacteria that can grow on this medium produce an enzyme, citrate-permease , capable of converting citrate to pyruvate . Pyruvate can then enter the organism’s metabolic cycle for the production of energy . Growth is indicative of utilization of citrate, an intermediate metabolite in the Krebs cycle . When the bacteria metabolize citrate , the ammonium salts are broken down to ammonia , which increases alkalinity . The shift in pH turns the bromthymol blue indicator in the medium from green to blue above pH 7.6. Christensen developed an alternative citrate test medium that does not require the organism

Urease Test

Urease Test The urease test is used to determine the ability of an organism to split urea, through the production of the enzyme urease. Principle Urea is the product of decarboxylation of amino acids . Hydrolysis of urea produces ammonia and CO2 . The formation of ammonia alkalinizes the medium, and the pH shift is detected by the color change of phenol red from light orange at pH 6.8 to magenta (pink) at pH 8.1. Rapid urease-positive organisms turn the entire medium pink within 24 hours. Weakly positive organisms may take several days, and negative organisms produce no color change or yellow as a result of acid production . Uses 1. This test is used to differentiate organisms based on their ability to hydrolyze urea with the enzyme urease. 2. This test can be used as part of the identiﬁcation of several genera and species of Enterobacteriaceae, including Proteus, Klebsiella ,

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