Analysis of factors affecting fluctuations in urinary oxygen tension and relationship to obligate anaerobic bacterial growth

PURPOSE: Obligate anaerobes are infrequently detected in routine urine cultures, potentially due to increased urinary oxygen tension (UpO2) following air exposure, which compromises their viability. This study evaluates time-dependent changes in UpO2 and their impact on the viability of obligate anaerobes in urine to improve diagnostic accuracy in suspected anaerobic urinary tract infections (UTIs). METHODS: Urine samples from healthy volunteers were stored in containers and monitored for UpO2 over time. Bacteroides fragilis and Fusobacterium nucleatum were inoculated into urine samples, and bacterial viability was assessed under aerobic and anaerobic conditions at multiple time points. RESULTS: The average UpO2 level immediately after urine collection was 66.9 Torr. No significant correlation was found between UpO2 levels and factors such as age, sex, urine dipstick test results, time of urine collection, or the interval between urinations. UpO2 increased significantly upon air exposure, whereas CO2-filled containers (Kenkiporter II) effectively maintained low oxygen tension. B. fragilis and F. nucleatum did not affect the changes in UpO2. Under aerobic conditions, B. fragilis remained viable for up to 1440 min (24 h), while F. nucleatum showed marked oxygen sensitivity and was undetectable in smear testing after 360 min. CONCLUSION: This study highlights the importance of minimizing oxygen exposure in urine samples. When anaerobic UTIs are suspected, immediate anaerobic culture using appropriate containers should be considered to improve detection rates and avoid false negatives.