File:Klebsiella pneumoniae Mucoid Colonies on MacConkey Medium.jpg

English: Klebsiella pneumoniae is a type of bacteria that can cause various infections, including pneumonia, urinary tract infections, and bloodstream infections. When cultured on a MacConkey agar medium, certain characteristics of the bacteria, including colony morphology, can be observed. MacConkey agar is a selective and differential medium used to grow and differentiate gram-negative bacteria, particularly members of the family Enterobacteriaceae, which includes Klebsiella pneumoniae. Here's how mucoid colonies of Klebsiella pneumoniae might appear on MacConkey agar:Colony Shape and Size: Mucoid colonies of Klebsiella pneumoniae tend to be larger in size compared to other bacterial colonies on the medium. They often appear as raised, rounded colonies.Color: Mucoid colonies of Klebsiella pneumoniae on MacConkey agar typically have a pink to dark pink coloration. The color change is due to the pH indicator in the medium, which changes color when lactose fermentation occurs.Mucoid Appearance: The term "mucoid" refers to the appearance of the colony's surface. Mucoid colonies are often slimy, moist, and somewhat glistening. This mucoid appearance is due to the production of a thick capsule around the bacterial cells, which is a characteristic feature of Klebsiella pneumoniae. Lactose Fermentation: Klebsiella pneumoniae is a lactose-fermenting bacterium, which means it can break down lactose sugar into acidic byproducts. This leads to the change in color of the medium, as mentioned earlier. The lactose fermentation can create a slightly acidic environment, turning the pH indicator in the agar pink.Selective Properties of MacConkey Agar: MacConkey agar contains bile salts and crystal violet, which inhibit the growth of gram-positive bacteria. As a result, it selects for the growth of gram-negative bacteria, including Klebsiella pneumoniae.