Stone Culture Positive Veillonella in Analysis of Calcium-Based Stones: A Case Report

Abstract

Background: Calcium-based urinary stones rarely grow bacteria on stone culture. The presence of an anaerobic bacteria is even more uncommon. We present a case of Veillonella growth from a primarily calcium phosphate-based urinary stone culture.

Case Presentation: A 56-year-old Caucasian woman presented with urosepsis and bilateral nephrolithiasis. A nephrostomy tube was emergently placed in the left kidney. After resolution of her urosepsis, she underwent a left percutaneous nephrolithotomy. The stone culture grew Veillonella, a gram-negative anaerobe.

Conclusion: Growth of anaerobic bacteria, such as Veillonella, on stone culture of a calcium-based stone is a rare occurrence; the mechanism of this association remains unexplained.

Introduction

The primary mechanism of calcium-based stone formation is supersaturation of the urine with calcium oxalate and calcium phosphate. However, correction of elevated supersaturation with dietary recommendations and medications at times fails to prevent stone recurrence, indicating that additional factors play a role in stone formation. Although urease-positive bacteria are known to lead to the formation of struvite stones, bacteria may also play a role in calcium-based stone formation. We present a case of percutaneous removal of a calcium phosphate (hydroxy- and carbonate-apatite) stone, the culture of which produced Veillonella, a gram-negative anaerobe.

Case Report

The patient is a 56-year-old woman with a prior history of bilateral nephrolithiasis requiring bilateral percutaneous nephrolithotomy (PCNL) and bilateral shockwave lithotripsy. In April 2020, she presented to the hospital with urosepsis and new onset atrial fibrillation. CT scan revealed a 22 × 16 × 19 mm right lower pole stone; the left kidney was markedly hydronephrotic and contained multiple stones (Fig. 1) along with an obstructed dilated upper pole calix containing small pockets of air consistent with emphysematous pyelitis (Fig. 2). She was started on intravenous antibiotics and underwent emergent left upper pole nephrostomy tube placement; her atrial fibrillation resolved spontaneously as soon as the collection was drained. Urine collected from the left kidney grew Veillonella and Escherichia coli. After antibiotic therapy with ceftriaxone rendered her urine sterile, she underwent a left PCNL using the previous nephrostomy tract. A combined antegrade and retrograde approach was used for the PCNL, as is the routine procedure at our institution. This approach allows for controlled collecting system puncture and tract dilatation under direct observation. The stones were fragmented with the holmium laser (Cook Medical, Inc., Bloomington, IN) and extensively basketed both antegrade and retrograde. Stone analysis showed 30% calcium oxalate monohydrate, 10% calcium oxalate dihydrate, and 60% calcium phosphate (hydroxy- and carbonate-apatite). Urine culture from her kidney at the time of the procedure showed no growth; however, the stone culture grew both E. coli and Veillonella, an anaerobe. An uneventful second-look left ureteroscopy and a right PCNL, utilizing the same approach as the left, were performed two months later. The right stone culture grew Enterococcus faecalis and viridans streptococci but was unfortunately not sent for anaerobic culture.

FIG. 1.

CT scan images showing the stone burden.

FIG. 2.

CT scan showing left upper pole fluid collection and air.

Discussion

Veillonella is an anaerobic gram-negative diplococci normally observed in oral, gastrointestinal, and genital flora.¹ Clinically, Veillonella spp. are commonly associated with bite wounds but are considered to be generally harmless. Veillonella is uncommonly cultured from the urine; indeed, to the best of our knowledge, only two reports exist in the literature that link Veillonella spp. to infections of the urinary tract.^1,2

The majority of calcium stone cultures have no bacterial growth; however, E. coli is the most frequent bacteria associated with calcium-based urolithiasis. A study by Dornbier et al. analyzing the stone culture of 52 nonstruvite stones reported Enterobacteriaceae, Pseudomonas, Streptococcus, Corynebacterium, Haemophilus, Lactobacillus, Bifidobacterium, Proteus, and a solitary instance of Veillonella growth.³

Calcium-based stones have historically been considered noninfectious; however, recent evidence suggests that bacteria may play a role in their formation. Several mechanisms regarding stone formation with associated bacteriuria have been explored. Bacteria such as Klebsiella and E. coli have been observed to aggregate around calcium oxalate crystals.⁴ Also, many bacteria, including Klebsiella and E. coli, produce citrate lyase and thereby may decrease urinary citrate, a known inhibitor of calcium stone formation. In addition, E. coli has been found to increase the expression of stone matrix proteins in the renal tubular epithelium. The ability of anaerobic bacteria in particular to facilitate stone formation has yet to be investigated.

Veillonella spp. are most notable for their lactate fermenting ability, forming propionate, acetic acid, and carbon dioxide and hydrogen gas as a result. They do not metabolize citrate, which is counterintuitive to their potential ability to facilitate stone formation. In addition, Veillonella spp. are nonmotile, convert nitrates to nitrites, and produce indole. It is unknown how any of these characteristics might contribute to stone formation.

Veillonella is susceptible to a wide range of antibiotics, most commonly penicillins and cephalosporins. The two urinary tract infections linked with Veillonella reported in the literature were treated with ampicillin and ceftriaxone, respectively.^1,2 Veillonella has not been associated with emphysematous pyelitis, whereas E. coli is the most common causative pathogen. As such, in our case, E. coli was likely the cause of emphysematous pyelitis.

In general, anaerobic infections in the urinary tract are associated with abscesses rather than urinary tract infections or infection stones. Anaerobic organisms are rarely associated with stone formation, although commonly, stone cultures do not include a search for anaerobic bacteria. Our case indicates that anaerobic culture may warrant inclusion when performing a stone culture.

Conclusion

The presence of the anaerobic bacterium Veillonella in a calcium-based stone appears to be a rare event. The mechanism of stone formation and the frequency of anaerobic bacteria in calcium stone formers has yet to be explored.

Abbreviations Used

CT

computerized tomography

PCNL

percutaneous nephrolithotomy

Disclosure Statement

No competing financial interests exist.

Funding Information

No funding was received for this article.

Cite this article as: Karani R, Imani G, Tapiero S, Clayman RV (2020) Stone culture positive Veillonella in analysis of calcium-based stones: a case report, Journal of Endourology Case Reports 6:4, 396–398, DOI: 10.1089/cren.2020.0140.