Which group of bacteria is typically the first to colonize the upper respiratory tract in humans?

• A. Streptococci
• B. Escherichia coli
• C. Staphylococci
• D. Pseudomonas aeruginosa

Answer: (A)

Verified step by step guidance

1. Understand the concept of microbial colonization: The upper respiratory tract is normally colonized by a variety of bacteria shortly after birth, and the first colonizers play a crucial role in establishing the microbial community and preventing pathogen invasion.
2. Recall common bacterial groups found in the upper respiratory tract: Streptococci and Staphylococci are common residents, while Escherichia coli and Pseudomonas aeruginosa are more typically associated with the gut and environmental or opportunistic infections, respectively.
3. Focus on the characteristics of Streptococci: These bacteria are gram-positive cocci that are often the first to colonize mucosal surfaces, including the upper respiratory tract, due to their ability to adhere to epithelial cells and thrive in that environment.
4. Compare with Staphylococci: Although Staphylococci are also common colonizers of the skin and nasal passages, they generally colonize after Streptococci have established themselves.
5. Conclude that Streptococci are typically the first group to colonize the upper respiratory tract based on their ecological niche and colonization patterns in humans.