Calculous pyelonephritis caused by biofilm-forming Staphylococcus epidermidis: a case report

Staphylococcus epidermidis rarely causes urinary tract infections (UTIs) compared to gram-negative rods; however, biofilms formed on urinary calculi or debris can persist and lead to refractory infection. Here, we report a case of S. epidermidis-induced pyelonephritis with bacteremia in a patient referred for evaluation of a mass in the left renal pelvis. The patient presented to the emergency department with fever and left flank pain and was admitted with suspected pyelonephritis. He had a history of chronic pyuria and intermittent fever suggestive of bacteremia. Blood and urine cultures yielded S. epidermidis, which had previously been detected in the urine. Although his clinical parameters initially improved after emergency ureteral stent placement and intravenous antimicrobial therapy, the infection proved intractable. Therefore, left nephroureterectomy was performed to remove the calculus, control the persistent infection, and exclude the possibility of malignancy. Scanning electron microscopy of the harvested calculus revealed a dense biofilm on and surrounding the stone. In vitro phenotypic analysis demonstrated that one of two clinical isolates from the patient exhibited a markedly stronger biofilm-forming capacity, supporting the conclusion that a biofilm-mediated process limited antimicrobial efficacy. This case underscores that although UTIs by S. epidermidis are uncommon, they can be severe and persistent due to biofilm formation on urinary calculus with mass-like lesion. When S. epidermidis is detected in both blood and urine from patients with nephrolithiasis, clinicians should suspect biofilm-associated infection, evaluate the obstructing material, and consider early source control in addition to antibiotic therapy to prevent treatment failure and improve outcomes.