a,b,c,d eLab4. Selective and Differential Media Videos: Selective Media. MacConk

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a,b,c,d

eLab4. Selective and Differential Media Videos: Selective Media. MacConkey; EMB and Hektoen Enteric Mannitol Salt Agar Blood Agar Answer the following questions: a. Why are different selective and differential media used in a diagnostic lab? b. Why the necessity of selecting Gram negative enterics? c. Differentiate and explain the different types of blood hemolysis and their significance. d. Under what conditions would one' experience blood hemolysis? Week 3: Lab 5. Biochemical Tests Part1 10 /12 Download Print Open with docReader Reflect in ePortfolio Activity Details

Explanation / Answer

a. Different selective and differential media are used in a lab for the growth of the desired microorganism. Selective media promote the growth of the desired microorganism and inhibit the growth of rest of microorganims. Differential media help to distinguish between groups of microorganims on the same medium. Both these media help in the isolation of microorganisms responsible for various diseases.

b. Gram negatve enterics have their natural habitat in the intestinal tract of humans and animals. Some of these are part of the normal microbiota of the gut whereas others are the causative agents of many diseases. Gram negative enterics such as Salmonella and Shigella are pathogenic bacteria and are the causative agents of Typhoid and Shigellosis, respectively. Therefore these bacteria need to be selected for their isolation and detection of the illness.

c. There are following types of hemolysis: alpha, beta and gamma.

Alpha hemolysis is caused by hydrogen peroxide produced by the bacteria, oxidising hemolglobin to green coloured methemoglobin. It exhibits incomplete hemolysis.

Beta hemolysis is the complete lysis of red blood cells in the media surrounding the colony. It is caused due to the production of Streptolysin, an exotoxin responsible for Beta hemolysis.

Gamma hemolysis means no hemolysis of red blood cells in the media surrounding the colony. It does not cause any change in the colour of the media.

d. Hemolysis can occur due to a large number of medical conditions such as :

Infection with Gram positive bacteria such as Streptococcus, Enterococcus nd Staphylococcus.

Parasitic infection such as Plasmodium

Hemolytic disease of newborn

Hemolytic anemia

Sickle cell disease and G6PD deficiency

Cetain medications such as Penicllin, acetaminophen.

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