Medical

I.             Alternative test for Gram Reaction – 3% Potassium Hydroxide A.     Add a heavy inoculum of pure culture of bacteria grown on a solid medium to a drop of 3% potassium hydroxide (KOH) solution (3 grams KOH per 100 mL distilled water) on a clean glass slide. B.      Stir for about one minute, occasionally lifting the loop to look for thickening and “stringing” of the slurry. 1.Gram negative        2 . Gram positive Result: 1.            Gram positive:  bacteria will not appear to change the viscosity of the KOH solution. 2.           Gram negative: bacteria will cause the KOH solution to become stringy or mucoid in appearance and consistency. D.     QUALITY CONTROL: 1.        ...

           Gram Stain for bacteriology Gram stain pure strain cultures to determine whether Gram negative or Gram positive. Gram staining detects a fundamental difference in the cell wall composition of bacteria. A.     Prepare a bacterial smear from a pure culture 1.           Put a drop of saline, distilled water, or PBS on a clean glass slide 2.           Using a sterile loop or needle touch an isolated colony and mix in the water drop. 3.           Mix until just slightly turbid (light inoculum is best, excess bacteria will not stain properly). 4.           Let air dry and heat fix. Do not overheat; slide should not be too hot to touch. 5.           Allow to cool. B.  ...

MacConkey Agar MacConkey agar  is a selective and differential media used for the isolation and differentiation of non-fastidious gram-negative rods, particularly members of the family Enterobacteriaceae . Composition MacConkey agar is used for the isolation of gram-negative enteric bacteria and the differentiation of lactose fermenting from lactose non-fermenting gram-negative bacteria.  Pancreatic digest of gelatin  and  peptones (meat and casein)  provide the essential nutrients, vitamins and nitrogenous factors required for growth of microorganisms.  Lactose monohydrate  is the fermentable source of carbohydrate. The selective action of this medium is attributed to  crystal violet  and  bile salts,  which are inhibitory to most species of gram-positive bacteria.  Sodium chloride  maintains the osmotic balance in the medium. ...

Simmons Citrate Agar Simmons Citrate Agar  is an agar medium used for the differentiation of Enterobacteriaceae based on the utilization of citrate as the sole source of carbon.  Ingredients per liter of deionized water: Principle of Simmons Citrate Agar Uses of Simmons Citrate Agar 1.     It is used for the differentiation of Gram-negative bacteria on the basis of citrate utilization. 2.     Simmons Citrate Agar may be used to differentiate citrate-positive  Salmonella enteritidis  and members of  Salmonella  subgenus II, III and IV from the citrate-negative  Salmonella typhi, Salmonella paratyphi  A,  Salmonella pullorum  and  Salmonella gallinarum . 3.     Simmons Citrate Agar is primarily used to aid in the identification of Enterobacteriaceae. Uses include: Escherichia coli ...

Mannitol Salt Agar for the isolation of Staphylococcus (MSA) Mannitol Salt Agar (MSA) is used as a selective and differential medium for the isolation and identification of  Staphylococcus aureus  from clinical and non-clinical specimens. It encourages the growth of a group of certain bacteria while inhibiting the growth of others. It is a selective medium prepared according to the recommendations of Chapman for the isolation of presumptive pathogenic staphylococci. Composition of Mannitol Salt Agar  Sodium Chloride 75.0gm Proteose Peptone 10.0gm Mannitol 10.0gm Beef Extract 1.0gm Phenol Red 0.025gm Agar 15.0gm Distilled Water = 1000 ml Final pH 7.4 ± 0.2 at 25°C. Principle of Mannitol Salt Agar Mannitol Salt Agar contains  peptones  and  beef extract,  which supply nitrogen, vitamins, minerals and amino acids essential for growth. The 7.5% concentration of  sodium chl...