Cultivation and molecular characterization of Foley catheterized urine, clean catch urine, and vaginal swabs from pregnant women prior to delivery

The bladder and urine have historically been considered sterile, especially in the context of clinical assessment. Yet, enhanced culture techniques and advances in DNA sequencing surveys have revealed a low microbial biomass microbiota in the bladders of most healthy individuals. Yet very few studies have investigated the urinary microbiota of pregnant women, who are at increased risk of urinary tract infections (UTIs) that can lead to pregnancy complications such as spontaneous preterm birth. To better understand the potential role of a bladder microbiota during pregnancy, we characterized the urinary microbiota of 25 pregnant women (delivering at or beyond 36 weeks gestation) by comparing the bacterial profiles of their paired catheter urine, clean catch urine, and vaginal swabs through both cultivation and molecular microbiological survey methods. For culture, three bacterial taxa were detected in at least 20% of all urine samples (Lactobacillus species, coagulase negative Staphylococcus species, and Ureaplasma urealyticum). All three taxa were detected less frequently in Foley catheter urine than in clean catch urine. Ureaplasma urealyticum was the most frequently recovered bacterium in Foley catheter urine (13/25 women). It was also identified as being more relatively abundant in Foley catheter urine than in the vagina through 16S rRNA gene surveys. Other lower abundance Gram-positive anaerobic cocci (i.e., Finegoldia and Anaerococcus) were also more relatively abundant in Foley catheter urine than clean catch urine or vaginal swabs. However, all sample types had high relative abundances of Lactobacillus and Gardnerella species. Overall, this suggests that, although vaginal microbiota contamination cannot be completely avoided, Foley catheterized urine is effective at characterizing the low abundance bladder microbiota, including Ureaplasma, Finegoldia, and Anaerococcus species. This warrants their further consideration as commensal members of the bladder microbiome during pregnancy.