Question

1.) How could MacConkey agar aid in the identification of coliforms?
2.) Streptococcus Uniate ferments mannitol. Could MacConkey agar be used to isolate S. iniae from a complex mixture?

Answer 1

Answer-

According to the given question-

MacConkey agar medium-

• MacConkey Agar media is a type of both  selective and differential medium used for the isolation of gram negative bacteria such as well as enteric bacilli.
• In this media only those microorganism can survive which can tolerate the salt concentration present in the medium.
• This media contains Lactose, Peptone, Bile salts , Crystal violet, Neutral red,  Sodium chloride, and Agar.
• the presence of Crystal violet and bile salt responsible for inhibiting the growth of gram positive bacteria.
• this media also contains carbohydrate Lactose which is serve as the source of energy. This media is also used for the differentiation of those gram negative bacteria which are capable of fermenting lactose into acids and due to which the pH of the medium decreases below 6.8.
• The lactose fermenting bacteria appeared as pink while those which are not capable of fermenting lactose are appeared colorless.
• Coliform bacteria are non-spore forming, Rod shaped   belongs to the group of Gram-negative bacteria. they are generally found in the digestive tract as well as in the waste of humans. they are also capable of fermenting lactose and produces acid and turn the pH and change the color. so the coliform bacteria can be easily differentiated from the other enteric microorganisms.

(2)  Streptococcus iniae is sphere-shaped belongs to the group of Gram-positive bacteria. Mannitol Salt Agar is also used as  the selective and differential media. Microorganisms that are belongs to  genus Staphylococcus such as Staphylococcus aureus, can tolerate the high salt concentration and also have the capability to ferment  sugar mannitol and produces acid which leads to decrease in pH and changes the medium to yellow.

• we have already described that the MacConkey agar is used for the isolation based on the lactose fermentation gram negative bacteria but the  S. iniae is a gram positive bacteria which can ferment sugar mannitol but not lactose sugar. so the MacConkey agar can not be used for the isolatation of  S. iniae from a complex mixture.