A common member of the normal flora of the upper respiratory tract is which organism?

• A. Corynebacterium jeikeium
• B. Lactobacillus
• C. Staphylococcus epidermidis
• D. Viridans streptococcus

Answer: (D)

The main idea is that the upper respiratory tract hosts a community of normal, resident bacteria, with viridans group streptococci being classic inhabitants of the oral cavity and nasopharynx. These streptococci are part of the usual flora in this region and help populate the mucosal surfaces, often existing harmlessly but capable of causing infections if they enter the bloodstream.

Viridans streptococci are commonly found around the teeth and in the oropharynx, making them a typical example of upper respiratory tract commensals. They are usually alpha-hemolytic and do not rely on optochin sensitivity to define their role in the URT, which matches their well-known presence in the mouth and throat.

The other organisms listed are more characteristic of other sites: Corynebacterium jeikeium tends to be skin and mucosal flora; Lactobacillus is typical of the gastrointestinal and female genital tracts; Staphylococcus epidermidis is predominantly a skin inhabitant and less characteristic of the URT as a stable resident.