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Case 3 Answer

Gina comes to your office with a sore throat. Vital signs: temperature 102 degrees C, pulse 95 bpm, respirations 23/min, blood pressure 120/85. Erythema and edema are noted on and around the tonsils with a purulent exudate present on the tonsils. No cough was noted. Anterior cervical lymph nodes are enlarged. Gina’s throat was swabbed and sent to the microbiology lab. Lab results: Gram-positive cocci, catalase negative, Beta-hemolysis on blood agar, sensitive to bacitracin. Which of the following is the most likely cause of Gina’s sore throat?

1. Corynebacterium diphtheriae - causes diphtheria but would have a pseudomembrane and the organism is a gram positive rod; nonhemolytic on blood agar
2. Mycoplasma hominis- does not grow on blood agar plates
3. Streptococcus pneumoniae - is a gram positive alpha hemolytic coccus sensitive to optochin
4. Streptococcus pyogenes - this organism is the most common cause of bacterial pharyngitis*
5. Staphylococcus aureus - a gram positive catalase positive coccus; either non-hemolytic or beta-hemolytic

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Site Last Revised 11/12/13
Neal Chamberlain, PhD. A. T. Still University of Health Sciences/Kirksville College of Osteopathic Medicine.

Take Care and Think Microbiologically!