Question 288

Question:

A 9 year old girl presents with 2 days of sore throat and fevers of 102ºF. Physical exam reveals an erythematous pharynx with a white, creamy exudate covering the left tonsil. Palpation of the neck reveals an extremely tender left submandibular lymph node. Throat cultures were taken and reveal beta-hemolytic colonies on blood agar. Susceptibility analysis show growth is not inhibited by amoxicillin, and erythromycin. Growth is inhibited by bacitracin. Which of the following is the mostly likely causal organism?

Correct Answer: B.  Streptococcus pyogenes

There are multiple organisms that can cause exudative pharyngitis; however, the results of the throat culture determine the final diagnosis. More specifically, Streptococcus pyogenes (choice B) can be correctly identified on culture based upon its characteristics of beta-hemolysis and susceptibility to bacitracin.

Rhinovirus (choice A) and Epstein-Barr virus (choice D) cannot be cultured on blood agar.

Streptococcus agalactiae (choice C) is a beta-hemolytic strep, but it is bacitracin-resistant and therefore not an appropriate answer. A more typical presentation of S. agalactiae is meningitis in newborns.

Candida albicans (choice E) can cause oral thrush; however, it seldom causes pharyngitis in non-immunocompromised individuals. Additionally, it does not grow beta-hemolytic colonies on blood agar.