Answer:
The correct answer is option - adhesins.
Explanation:
Appendages of bacteria or microbial virulence factor adhesins that help in adhesion or attachment to host cells or surfaces of hosts. These are essential microbial virulence factors to bind with the host respiratory tissues.
bronchitis, pneumonia and other microbes cause respiratory infection and for this adherence is the most essential step that is regulated by adhesins.
Thus, the correct answer is adhesins.