A 4-month-old female infant was admitted to the hospital with a history of prolonged diarrhea and severe failure to thrive. The patient's diarrhea started when she was 2 months old which prompted hospitalization a month later for further investigation. Discontinuation of enteral feeding resulted in resolution of her diarrhea, and total parenteral nutrition was continued via a central venous catheter (CVC).

After 10 days, she developed fever. Physical examination was unremarkable except for a black discoloration of the tongue (Fig. 1). Empirical antibiotic treatment was provided with ceftriaxone. However, early report of a gram-positive growth in blood cultures at 48 h prompted addition of vancomycin to the treatment regimen. This growth was later identified as Kocuria (Micrococcus) kristinae, which was detected in two separate aerobic blood cultures. The patient showed a dramatic response to vancomycin treatment, and blood cultures obtained 48 h later from the indwelling CVC and from a peripheral vein were negative. The black discoloration of the tongue completely resolved a week after initiation of vancomycin treatment (Fig. 2), and combination antibiotic therapy was discontinued after a total of 14 days. To the best of our knowledge, this is the first reported case in the English literature of K. kristinae bacteremia as a cause of black hairy tongue.

Fig. 1
figure 1

Black discoloration of the dorsal tongue

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Fig. 2
figure 2

Discoloration resolution after treatment

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