Why is the polymerase chain reaction (PCR) assay considered more sensitive and specific than the coliforms culture test for detecting microbial contamination?

• A. PCR detects only living bacteria, while culture tests detect both living and dead cells.
• B. Coliforms culture test can detect all types of microorganisms, making it more specific.
• C. PCR amplifies specific DNA sequences, allowing detection of even small amounts of target organisms.
• D. PCR relies on the growth of bacteria on selective media, which increases sensitivity.

Answer: (C)

Verified step by step guidance

1. Step 1: Understand the principle behind PCR. PCR (Polymerase Chain Reaction) amplifies specific DNA sequences of the target microorganism, which means it can detect even very small amounts of DNA present in a sample.
2. Step 2: Recognize that PCR's specificity comes from the use of primers—short DNA sequences designed to bind only to the DNA of the target organism—ensuring that only the desired DNA is amplified.
3. Step 3: Compare this to the coliform culture test, which relies on growing bacteria on selective media. This method depends on viable (living) bacteria being able to grow and form colonies, which can limit sensitivity if bacteria are present in low numbers or are stressed.
4. Step 4: Note that culture tests may not detect bacteria that are viable but non-culturable, or those present in very low numbers, whereas PCR can detect DNA regardless of the bacteria's growth state, increasing sensitivity.
5. Step 5: Conclude that PCR's ability to amplify specific DNA sequences rapidly and detect low levels of target organisms makes it both more sensitive and more specific than traditional culture-based coliform tests.