Which of the following are typically the first microbes to colonize the upper respiratory tract in humans?

• A. Streptococcus species
• B. Clostridium botulinum
• C. Escherichia coli
• D. Mycobacterium tuberculosis

Answer: (A)

Verified step by step guidance

1. Understand the concept of microbial colonization: The first microbes to colonize a body site are usually those that are well-adapted to the environment and can thrive in the conditions present there.
2. Consider the environment of the upper respiratory tract: It is exposed to air, has mucous membranes, and is a site where many microbes can attach and grow without causing immediate harm.
3. Evaluate each option based on typical habitat and pathogenicity: Clostridium botulinum is primarily found in soil and is not a common colonizer of the respiratory tract; Escherichia coli is mainly found in the intestinal tract; Mycobacterium tuberculosis is a pathogen that infects the lungs but is not a normal colonizer.
4. Recognize that Streptococcus species are part of the normal flora of the upper respiratory tract and are commonly the first colonizers after birth, establishing a stable microbial community.
5. Conclude that Streptococcus species are typically the first microbes to colonize the upper respiratory tract due to their adaptation to this environment and their role as normal flora.