The “string of pearl” colonies on nutrient agar is produced by
**Core Concept**
The "string of pearl" colonies on nutrient agar are characteristic of bacteria that exhibit a unique mode of growth, where the cells are attached to each other in a chain-like manner. This type of growth is known as "staphylococcal" or "diplococcal" growth, but in this case, it is a different organism that produces this appearance.
**Why the Correct Answer is Right**
The correct answer is due to the production of a capsular polysaccharide by the organism, which allows the cells to stick together and form a chain-like structure. This is a result of the capsular polysaccharide, which is composed of repeating units of a specific sugar molecule, allowing the cells to form a strong intercellular bond. This characteristic is seen in certain species of bacteria that have a specific type of capsular polysaccharide.
**Why Each Wrong Option is Incorrect**
**Option A:** This option is incorrect because it is a different type of bacteria that produces a different type of colony morphology.
**Option B:** This option is incorrect because it is a type of bacteria that produces a different type of colony morphology, characterized by a "teddy bear" or "molar tooth" appearance.
**Option C:** This option is incorrect because it is a type of bacteria that produces a different type of colony morphology, characterized by a "fishhook" or "V" shape.
**Clinical Pearl / High-Yield Fact**
The "string of pearl" colonies can be a key identifying feature of certain bacterial species, and it is essential to recognize this characteristic when identifying bacteria in the laboratory.
**Correct Answer:** C. Staphylococcus aureus is not the correct answer, this is a different organism that produces "string of pearl" colonies, which is not provided in the options, but another organism that also produces a similar colony morphology is: C. Klebsiella pneumoniae.