Answer to December 2018 Photo Quiz

Answer: Sarcina ventriculi. The 16S rRNA sequencing confirmed the isolate as Sarcina ventriculi, with a 99.35% match to the database entry.

Sarcina spp. are large (up to 3 μm in diameter), sphere-shaped, anaerobic, Gram-positive cocci which typically form clusters of tetrads or octets. The genus name Sarcina derives from the New Latin word meaning “bundle.” Two species associated with human infection are Sarcina ventriculi and S. maxima (1). Sarcina is a member of the Clostridiaceae and related to the genus Clostridium; its taxonomy is currently under evaluation and may change in the future (2).

Since its discovery in the stomach of a patient with abdominal bloating and vomiting in 1842, S. ventriculi has been identified primarily on histopathology by surgical pathologists and appears to be increasingly reported in the pathology literature within the past 5 years (1, 3). On the other hand, Sarcina is not even mentioned in many of the routine clinical microbiology textbooks. On histology, the organisms appear as packets of large Gram-positive cocci in tetrads or octets. Although most often detected histologically on gastric biopsy specimens from patients with gastroparesis and other gastrointestinal disorders, Sarcina has also been noted on gastric biopsy specimens from asymptomatic patients (4). It has also been noted on a urine cytology specimen from a child with vesicoureteral reflux and pyuria. The presence of Sarcina in blood has been reported only twice before. The first report was in 1872, but the author failed to state how he confirmed its presence (5). The other report of Sarcina in blood was a case of bacteremia in a patient with congenital chloride diarrhea; however, the authors describe recovery from blood without indicating the culture method (6). The differential diagnosis on histology includes other Gram-positive cocci which can form tetrads, such as Micrococcus, but micrococci are smaller (approximately 0.5 μm in diameter). If the organism is cultivated in the clinical microbiology laboratory, the differential may include yeast, given its large size, its budding appearance, and its poor uptake of Gram stain; however, its obligate anaerobic growth identifies this as an anaerobic bacterium.

This patient's urine culture was positive for E. coli. Both blood and urine E. coli isolates were susceptible to all antimicrobials tested, including levofloxacin. The patient improved with a 14-day course of levofloxacin. It is not certain whether Sarcina played a pathogenic role in bloodstream infection in this patient. This anaerobe would not be cultivatable from routine aerobic urine culture. We believe that the source of Sarcina may have been either gastrointestinal or urogenital, given the history of vomiting and structural kidney abnormalities.

See https://doi.org/10.1128/JCM.01334-17 in this issue for photo quiz case presentation.