Question

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(1 pts) 16) Indicate whether phenol red lactose fermentation broth is a selective or differential media by marking the appropriate box(es). If the medium is both selective and differential, mark both. If the medium is neither selective nor differential, check the "neither" box: selective o differential Oneither (1 pts) 17) Indicate whether mannitol salt agar is a selective or differential media by marking the appropriate box(es). If the medium is both selective and differential, mark both. If the medium is neither selective nor differential, check the "neither" box: selective differential O neither (1 pts) 18) Indicate whether Mueller-Hinton agar is a selective or differential media by marking the appropriate box(es). If the medium is both selective and differential, mark both. If the medium is neither selective nor differential, check the "neither" box: selective differential neither (1 pts) 19) Indicate whether NaCl agar is a selective or differential media by marking the appropriate box(es). If the medium is both selective and differential, mark both. If the medium is neither selective nor differential, check the "neither" box: O selective differential neither

Answer 1

Question 16

Ans : Option 2

$\square$ Differential

Reason : Phenol Red Broth is a differential medium which is used to differentiate gram negative enteric bacteria. It contains phenol red (a pH indicator), and one carbohydrate (glucose, lactose, or sucrose). Phenol red is a pH indicator which turns yellow. If the organism is able to utilize the carbohydrate, an acid or gas by-product is created, which turns the media yellow. If the organism is unable to utilize the carbohydrate, gas will not be produced, and no color change.

Question 17

Ans : Option 1 and 2

$\square$ Selective

$\square$ Differential

Reason : Mannitol salt agar is both selective and differential medium. They are selective because high salt concentrations inhibits the growth of most gram-negative bacteria. The differential ingredient is the sugar mannitol. Organisms capable of using mannitol will produce acidic by products of fermentation that will cause the pH indicator, phenol red, to turn yellow. Staphylococcus aureus is capable of fermenting mannitol while Staphylococcus epidermidis is not.

Question 18

Ans : Option 3

$\square$ Neither

Reason : Mueller-Hinton agar is neither a selective nor a differential medium because almost all organisms plated on here will grow. They allow both gram positive as well as gram negative bacteria to grow and is used for antibiotic susceptibility testing.

Question 19

Ans : Option 1

$\square$ Selective

Reason : Salt (NaCl) acts as a selective agent and interferes with membrane permeability and osmotic equilibrium. Salt tolerant organisms will produce heavy growth in the broth. Organisms that do not grow on NaCl agar are not salt tolerant.