Which of the following is the most definitive means of identifying a microorganism in microbiology?

• A. Gram staining
• B. Observation of colony morphology on agar plates
• C. Genetic sequencing of the organism's DNA
• D. Measuring growth in liquid culture

Answer: (C)

Verified step by step guidance

1. Step 1: Understand the purpose of each method listed for identifying microorganisms. Gram staining differentiates bacteria based on cell wall properties, providing a broad classification into Gram-positive or Gram-negative groups.
2. Step 2: Recognize that observation of colony morphology on agar plates gives visual clues about the microorganism's characteristics, such as shape, color, and texture, but these features can be similar among different species.
3. Step 3: Consider measuring growth in liquid culture, which indicates the ability of the microorganism to multiply under certain conditions but does not provide specific identification information.
4. Step 4: Learn that genetic sequencing of the organism's DNA analyzes the exact nucleotide sequence, allowing precise identification at the species or even strain level by comparing sequences to known databases.
5. Step 5: Conclude that among the options, genetic sequencing is the most definitive method because it provides detailed molecular information that surpasses the resolution of staining, morphology, or growth characteristics.