Question

MacConkey agar questions 4. Would this bacteria be a Gram positive or a Gram negative? How do you know? 5. Does this bacteria ferment lactose? How do you know?

Answer 1

MacConkey agar questions 4. Would this bacteria be a Gram positive or a gram negative? How do you know? MacConkey agar is a selective for Gram- negative bacteria 5. Does this bacteria ferment lactose? How do you know? Lactose fermenting Gram-negative Bacteria produce Pink colonies in the MacConkey agar medium. The image provided is a MacConkey agar plate having colonies of E. Coli. Based on the characteristic morphology, lactose fermenting colonies of E Coli appear in dry, donut shaped and dark pink in color.

Question: 4. Would this bacteria be a Gram positive or a gram negative? How do you know? Answer: The bacterial colony shown in the image is of Gram-negative bacteria (eg. E. Coli) In bacteriology, MacConkey agar is a selective and differential culture medium that isolate Gram-negative bacteria and enteric bacilli. It differentiates various Gram- negative bacteria based on their ability to ferment lactose. MacConkey agar inhibits the growth of Gram-positive bacteria. It contains substances such as Bile salts and crystal violet that inhibit the growth of Gram- positive bacteria, and thus allows to isolate the Gram-negative bacteria within the medium. 5. Question: Does this bacteria ferment lactose? How do you know? Answer: Gram-negative bacteria that have the ability to ferment lactose produce pink colonies, whereas those cannot produce colorless colonies.