Question

D | Question 3 0.25 pts What will be the color of the agar if Staphyłococcus epidermidis grows on MSA plate? O Red O White D Question 4 0.25 pts If 1 gm of food sample was added into 99 ml of diluent, then what will be the dilution factor for the food sample? 0 10 dilution 102 dilution 10 dilution 10t dilution 0.25 pts D Question 5

Answer 1

question 3:

Answer is Red

Mannitol salt agar is a commonly used growth medium in microbiology. It encourages the growth of a group of certain bacteria while inhibiting the growth of others. It contains a high concentration (~7.5%-10%) of salt (NaCl), making it selective for gram positive bacteria Staphylococci (and Micrococcaceae) since this level of NaCl is inhibitory to most other bacteria.

It is also a differential medium for mannitol fermentors, containing mannitol and the indicator phenol red. Staphylococcus aureusproduce yellow colonies with yellow zones, whereas other Staphylococci produce small pink or red colonies with no colour change to the medium. If an organism can ferment mannitol, an acidic byproduct is formed that will cause the phenol red in the agar to turn yellow.

Question 4

if 1 gm of food diluted into 99 ml of diluent the dilution factor is as follows

The dilution factor is equal to the final volume divided by the aliquot volume

then 100mL/1 = 10² dilution