Which statement is true about E.coli on a MAC plate?

The correct statement about E. coli on a MacConkey (MAC) plate is that it is a lactose fermenter and will appear pink. MacConkey agar is a selective and differential culture medium used to isolate gram-negative bacteria and differentiate them based on lactose fermentation. E. coli ferments lactose, resulting in the production of acid, which changes the pH indicator in the medium and leads to the formation of pink colonies.

This characteristic is critical for identifying E. coli among other gram-negative organisms. The pink coloration indicates that lactose has been fermented, distinguishing E. coli from non-lactose fermenters, which typically produce colorless colonies on the same medium. Understanding the fermentation properties of E. coli on MacConkey agar assists laboratory personnel in diagnosing infections accurately and reporting results effectively.