Which microorganism forms colonies that appear embedded in agar, resembling a "fried egg"?

Mycoplasma pneumoniae is known for its unique colonial morphology when grown in specific laboratory conditions. It forms colonies that can be described as resembling a "fried egg" due to their irregular outer edges and a central depression, giving them a distinctive appearance that sets them apart from other bacteria. This characteristic is a direct result of their lack of a cell wall, which affects how they grow and interact with the agar surface.

In contrast, Mycobacterium kansasii typically forms more traditional colonies with a rough texture and does not share the same distinct "fried egg" appearance. Clostridium difficile usually produces colonies that are more opaque and can sometimes have a drippy or irregular form, while Ureaplasma urealyticum, similar to Mycoplasma, can have atypical growth patterns, but does not typically produce the characteristic fried egg morphology. This unique colonial trait of Mycoplasma pneumoniae is a key identifying feature used in laboratory settings for its identification.