Question

BI0S242, Week 7, Lab 1 2. Do all the bacteria samples grow on Eosin Methylene Blue and MacConkey agar? not, why What does a metallic green sheen indicate on an Eosin Methylene Bhue plate? 3. 4. What additional information did the lactose fermentation tubes provide? Why couldn't we examine any anaerobic bacteria that are part of the normal digestive system? 5. 6. Were there any colonies in the rest room samples? Could you identify any that gave similar results on EMB and MAC to the known samples?

Answer 1

2.Eosin methylene blue agar is specifically used for detecting gram negative bacteria.Fecal coliforms can be identified using the selective and differential method used.The growth of organism is purple to black .Apart from this non pathogenic and non lactose fermenting organism also grow in it.The presence of Eosin and methylene inhibits the growth of Gram+ bacteria.In simple they are lactose fermenter

Mackonkey agar is used to find gram negative and enteric bacilli.This is because the presence of crystal violet and bile salts cease the growthof gram positive bacteria,

3.If there is a vigorous fermentation in the EMB agar then a metallic sheen is produced..The lactose is fermented very fast leading to acid production and thus decreasing the pH makes the green color or green metallic sheen (E coli)

If the fermenter is weak it produces mucous pink color.In case oif it is colorless it neither ferment lactose or sucrose.

4.The additional information which can be seen from lactose fermentation tubes are

• It may contain lactose,glucose, iron termed as Triple Sugar Iron Agar
• Contains poorly oxygenated base or bottom called as Butt
• Some organism leads to the formation of gases which makes it appear bubbled
• Hydrogen sulphide is produced

5.Anaerobic bacteria can grow only in the area where there is no oxygen.It us found in the area where there is mucus .It cannot 've found in normal GIT because of its action towards immune system