Which of the following is a gram negative rod associated with respiratory infections?

Haemophilus influenzae is a gram-negative rod that is indeed associated with respiratory infections. This bacterium commonly resides in the upper respiratory tract and can cause a variety of illnesses, particularly in children and individuals with compromised immune systems. It is known for causing conditions such as pneumonia, bronchitis, and sinusitis.

Understanding the characteristics of Haemophilus influenzae helps clarify its pathogenic potential in respiratory infections—its ability to adhere to respiratory mucosa and evade host defenses contributes to its role as a significant pathogen. Additionally, it is one of the organisms that can lead to serious complications like epiglottitis and meningitis, particularly before the advent of effective vaccination strategies.

In contrast, the other organisms mentioned do not fit this specific profile as well. For instance, Shigella primarily causes gastrointestinal infections, Clostridium includes species that are mostly associated with anaerobic infections, and Staphylococcus aureus, while it can cause respiratory infections, is classified as a gram-positive cocci rather than a gram-negative rod.