Detection of Microbial Colonization of the Urinary Tract

Preoperative routine urine culturing might not represent relevant pathogens in patients with indwelling stents because stent cultures diverge from urine cultures in up to 50% of all patients. Even if microorganisms in biofilms may not provoke urinary tract infections, they might become relevant pathogens of bacteraemia and urosepsis during endoscopic urinary tract surgery.

Zumstein et al. [1] searched for methods other than standard preoperative urine cultures to identify bacteria with the aim to facilitate early identification of involved bacteria and guide the optimal treatment of postoperative urosepsis. Therefore, they compared the findings of different specimens, time points and detection methods for bacteria in 94 patients with ureteral stents undergoing secondary ureterorenoscopy. Urine and blood samples were taken one day before stenting and secondary intervention with ureterorenoscopic stone removal. Analysis of bacteria was done by determination of the number of colony forming units by plating and bacteria equivalents through qPCR of the 16S rRNA gene after removal of human DNA from the samples using the MolYsis™ Complete5 DNA extraction kit (Molzym, Germany).

A major finding was that the different assays poorly correlated with each other with little prediction of biofilm analysis by preoperative urine culture. 16S qPCR revealed that even in patients with negative routine urine cultures, non-cultivatable bacteria may be present, which could become relevant during surgery or any procedure leading to disruption of biofilms. The data raises doubt as regards the clinical relevance of preoperative identification of enterococci, staphylococci and streptococci. Consequently, the authors suggest that the timing of oral antibiotic prophylaxis might need to be reconsidered.