A challenging Microbiology Case Study


Case History :

A 24 year old male with a past medical history of recurrent streptococcal pharyngitis presents to the ED with a sore throat and dyspnea. His symptoms included :

1) Left-sided upper neck and lower jaw pain

2) Odynophagia.

3) Tachycardia,

4) Cervical lymphadenopathy,

5) A small left tonsillar abscess.

He has an elevated WBC count but blood cultures, Group A streptococcal and mononucleosis screens were negative.

The patient was admitted for pain management and treated with a combination of IV ampicillin/sulbactam (amp/sulb) and steroids. He improved with treatment and was discharged the following day on oral amoxicillin/clavulanic acid (amox/clav).

Nine days later, the patient re-presented with similar complaints. The tonsillar abscess had increased in size to 2cm. he had significant leukocytosis and a now positive Group A streptococcal screen. 2mL of pus was aspirated from the lesion but no cultures were ordered.

The patient’s status again improved, and he was discharged home again on oral amox/clav.

The patient returned the following day and was placed on IV amp/sulb and admitted for imaging and symptom management. A neck CT with contrast revealed a now 3cm tonsillar abscess with reactive cervical lymphadenopathy . A throat culture was collected; however, no beta-hemolytic streptococci were recovered after 48 hours of incubation. Incision and drainage of the abscess was performed at bedside, recovering an additional 10 mL of purulence that was sent to the microbiology laboratory for aerobic and anaerobic culture. The patient improved on IV amp/sulb and was switched to high dose amox/clav on day 15.


Laboratory Identification :


Gram stain of the aspirated purulence : a mixture of gram positive rods and cocci


The aerobic culture grew a heavy amount of tiny, weakly beta-hemolytic colonies on blood agar. Smears of these colonies revealed Gram-positive coryneform rods. Biochemical testing determined the growth to be catalase-negative and MALDI-TOF MS .

The anaerobic culture grew oral flora.


Kindly identify the isolated  gram positive rod ????


A case Discussion will be next week .

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