Abstract
BACKGROUND: Women presenting with typical symptoms of acute cystitis but with negative urine cultures, termed acute cystitis-like symptoms with negative urine cultures (ACNCs) in this study, are not uncommon. Despite previous attempts to detect bacterial DNA in urine, the etiology remains unclear. Although alterations in the urinary microbiome have been linked to other urological disorders, its involvement in ACNC has not been thoroughly investigated. METHODS: Between September 2016 and December 2017, midstream urine samples were collected from women aged ≥16 years who had at least one typical symptom of acute cystitis and a negative urine culture. Samples were obtained at the initial (V1) and follow-up (V2) visits. Shotgun metagenomic sequencing (SMG) was performed via an Illumina MiSeq system. Taxonomic analysis at the genus level included taxa with ≥10 assigned reads in samples with ≥10,000 human-subtracted reads (HSRs). RESULTS: Of 206 eligible women, 15 (7.3%; median age, 65 years) met the ACNC criteria and were enrolled. SMG was conducted for 15 samples at V1 and nine samples at V2. At V1, the HSR varied widely, and only five samples met the criteria for reliable interpretation. Seven samples, particularly those with high-grade pyuria, contained fewer than 1,000 HSRs, indicating potentially very low microbial loads or technical limitations. ACNC microbiomes demonstrated marked interindividual variation in taxonomic composition. The predominant taxa most frequently observed were Lactobacillus spp., Gardnerella spp., and JC polyomavirus. Conventional uropathogens, such as Escherichia spp., were not identified at interpretable levels. At V2, microbial diversity remained heterogeneous, but eight samples yielded sufficient read counts for interpretation. CONCLUSIONS: While conventional uropathogens below interpretable criteria are unlikely to be responsible for most ACNCs, it is not necessarily recommended to regard the leading taxon in each case as the cause or to exclude microbiological involvement simply due to a low HSR because no validated metagenomic signature distinguishes pathogens from commensals. However, the observed diversity in ACNC microbiome profiles may reflect a heterogenous group of microbial conditions, including potentially viral, and nonmicrobial etiologies.