Microbiological Characteristics of Infection-Related Urolithiasis: Comparative Analysis of Renal Pelvic Urine and Stone Cultures

Background. Infection-related urolithiasis is characterized by persistent microbial colonization and a high risk of recurrence, largely due to biofilm formation and the presence of bacteria within stone structures. Standard diagnostic approaches based on urine cultures may not fully reflect the underlying infectious process. Objective. To investigate the microbiological characteristics of infection-related urolithiasis by comparing bacteriological findings in renal pelvic urine and stone fragments obtained during percutaneous nephrolithotripsy (PCNL), and to assess their clinical significance. Materials and Methods. This study included 268 patients with infection-related urolithiasis who underwent PCNL. Bacteriological analysis of renal pelvic urine and intraoperatively obtained stone fragments was performed using standard culture techniques. Clinically significant bacteriuria was defined as ≥10⁴ CFU/mL. The distribution of microorganisms, concordance between urine and stone cultures, and intergroup comparability were evaluated using appropriate statistical methods. Results. Microbial colonization of stone fragments was detected in 61.2% of patients, while renal pelvic urine cultures were positive in 51.5% of cases. The most frequently isolated pathogens were Escherichia coli, Proteus mirabilis, and Enterococcus faecalis. Complete concordance of sterility between urine and stone cultures was observed in 37.3% of patients, whereas simultaneous infection of both materials was identified in 39.2%. In 16.4% of cases, stones were infected despite sterile urine, indicating the presence of hidden microbial reservoirs. No significant differences were found between study groups in baseline microbiological characteristics (p > 0.05). Conclusion. Infection-related urolithiasis is associated with a high prevalence of microbial colonization and frequent discordance between urine and stone cultures, highlighting the role of calculi as reservoirs of persistent infection and emphasizing the importance of comprehensive intraoperative microbiological assessment.

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