Microbiology Case Study: A 15 Year Old Male with Endocarditis

Case History

A 15 year old male with a past medical history significant for Tetralogy of Fallot (congenital heart defect), multiple valve replacements, chronic kidney disease, and prior Bartonella endocarditis. He presented with a “flu-like” illness including muscle aches, fevers, fatigue, and night sweats. His symptoms slowly dissipated after about three days. However, he had labs drawn including multiple blood culture sets which were all positive for growth.

Laboratory Findings

Gram stain showed gram positive bacilli and culture plates grew two morphologies of slow growing gray, granular and opaque colonies.This organism was identified by MALDI-TOF as Corynebacterium pseudodiphtheriticum.

Image 1. Gram stain with gram positive bacilli .
Image 2. Culture with small, grayish colonies with granular appearance and opaque centers (growth at day 2).


The genus Corynebacterium comprises a collection of irregular-formed, rod-shaped or coccoid bacteria that are non-motile, catalase-positive, and non-spore-forming.

Corynebacterium pseudodiphtheriticum (previously designated as Corynebacterium hofmannii) is a nonlipophilic, nonfermentive, urease- and nitrate-positive Corynebacterium species.1 C. pseudodiphtheriticum is part of the usual oropharyngeal bacterial flora, including the nares and throat. It appears to play a role in preventing colonization of oropharyngeal epithelia by pathogenic bacteria.

Most commonly, C. pseduodiptheriticum is a pathogen of the respiratory tract with cases of nosocomial and community-acquired pneumonia, bronchitis, tracheitis, pharyngitis, and rhinosinusitis. Endocarditis is the second most common infection site, although very rare. Cases of urinary tract and wound infections have also been reported.

Treatment is usually with penicillin alone or in combination with aminoglycosides. Antibiotic susceptibility profiling of C. pseudodiphtheriticum isolates showed that resistance to oxacillin, erythromycin, clindamycin, and macrolides are common.1


  1. Burkovski A. Corynebacterium pseudodiphtheriticum: Putative probiotic, opportunistic infector, emerging pathogen. Virulence. 2015;6(7):673–674. doi:10.1080/21505594.2015.1067747

-Nicole Mendelson, MD is a 1st year Anatomic and Clinical Pathology resident at the University of Vermont Medical Center.

-Christi Wojewoda, MD, is the Director of Clinical Microbiology at the University of Vermont Medical Center and an Associate Professor at the University of Vermont.

2 thoughts on “Microbiology Case Study: A 15 Year Old Male with Endocarditis”

Leave a Reply

Fill in your details below or click an icon to log in:

WordPress.com Logo

You are commenting using your WordPress.com account. Log Out /  Change )

Facebook photo

You are commenting using your Facebook account. Log Out /  Change )

Connecting to %s

This site uses Akismet to reduce spam. Learn how your comment data is processed.

%d bloggers like this: