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Human chorionic gonadotropin (hCG)

         Function   Human chorionic gonadotropin (hCG) is a glycoprotien hormone secreted by the developing placenta shortly after implantation.           Measuring hCG levels can be helpful in identifying a normal pregnancy, pathologic pregnancy, and can also be useful following an aborted pregnancy. There is also a benefit in measuring hCG in a variety of cancers including choriocarcinoma and extra-uterine malignancies          Smaller amounts of hCG are also produced in the pituitary gland, the liver, and the colon.  As previously mentioned, certain malignancies can also produce either hCG or hCG-related hormone.            The hormone itself is a glycoprotein composed of two subunits, the alpha and beta subunits.  There are multiple forms found in the serum and urine during pregnancy including the intact hormone and each of the free subunits. HCG is primarily catabolized by the liver, although about 20% is excreted in the urine. The beta subunit is degraded in the kidney to make a
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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 identiļ¬cation of several genera and species of Enterobacteriaceae, including  Proteus, Klebsiella ,

Bile Solubility Test

Bile Solubility Test Bile Solubility Test is the test which differentiate  Streptococcus pneumoniae  (positive- soluble) from alpha-hemolytic streptococci (negative- insoluble).  Streptococcus pneumoniae  is bile soluble whereas all other alpha-hemolytic streptococci are bile resistant. Principle  S. pneumoniae  has an autolytic enzyme which can be demonstrated by allowing a broth culture to age in the incubator; at 24 hours the broth is turbid; after a few days the medium will become clear. Bile or a solution of a bile salt (e.g., sodium desoxycholate) rapidly lyses pneumococcal colonies. Lysis depends on the presence of an intracellular autolytic enzyme, amidase. Bile salts lower the surface tension between the bacterial cell membrane and the medium, thus accelerating the organism’s natural autolytic process. Bile salts activate the autolytic enzyme which induces clearing of the culture. Reagents  Bile salt preparation 1-Prepare 10% bile salt solution for plate m