Pathogen-specific alterations in intestinal microbiota precede urinary tract infections in preterm infants: a longitudinal case-control study.

Urinary tract infections (UTIs) are among the most common late-onset infections in preterm infants, characterized by nonspecific symptoms and a pathogenic spectrum that diverges from that of term infants and older children, which present unique diagnostic and therapeutic challenges. Existing data on the role of gut microbiota in UTI pathogenesis in this demographic are limited. This study aims to investigate alterations in gut microbiota and fecal calprotectin levels and their association with the development of UTIs in hospitalized preterm infants. A longitudinal case-control study was conducted involving preterm infants admitted between January 2018 and October 2020. Fecal samples were collected weekly and analyzed for microbial profiles and calprotectin levels. Propensity score matching, accounting for key perinatal factors including age and antibiotic use, was utilized to match samples from UTI-diagnosed infants to those from non-UTI counterparts. Among the 151 preterm infants studied, 53 were diagnosed with a UTI, predominantly caused by Enterobacteriaceae (79.3%) and Enterococcaceae (19.0%). Infants with UTIs showed a significantly higher abundance of these families compared to non-UTI infants, for both Gram-negative and positive pathogens, respectively. Notably, there was a significant pre-UTI increase in the abundance of pathogen-specific taxa in infants later diagnosed with UTIs, offering high predictive value for early detection. Shotgun metagenomic sequencing further confirmed the dominance of specific pathogenic species pre-UTI and revealed altered virulence factor profiles associated with Klebsiella aerogenes and Escherichia coli infections. Additionally, a decline in fecal calprotectin levels was observed preceding UTI onset, particularly in cases involving Enterobacteriaceae. The observed pathogen-specific alterations in the gut microbiota preceding UTI onset offer novel insight into the UTI pathogenesis and promising early biomarkers for UTIs in preterm infants, potentially enhancing the timely management of this common infection. However, further validation in larger cohorts is essential to confirm these findings.