Characterization of a novel murine model of Staphylococcus saprophyticus urinary tract infection reveals roles for Ssp and SdrI in virulence.

Staphylococcus saprophyticus, an obligate human pathogen, is the most common Gram-positive causative agent of urinary tract infection (UTI) in young, healthy women. Despite the clinical importance of S. saprophyticus, little is known about how it causes disease in the urinary tract or how the host responds to the infection. Here we established an in vivo model to study both host and bacterial factors contributing to S. saprophyticus UTI. Using this model, we show that S. saprophyticus preferentially infects C3H/HeN murine kidneys instead of the bladder, a trait observed for multiple clinical isolates. Bacterial persistence in the kidneys was observed in C3H/HeN mice but not in C57BL/6 mice, indicating that host factors strongly contribute to the ability of S. saprophyticus to cause UTI. Using C3H/HeN mice as a model, histologic and immunofluorescence analyses of infected tissues revealed that S. saprophyticus induced epithelial cell shedding in the bladder and an inflammatory response characterized by macrophage and neutrophil infiltration in the bladder and kidneys. The inflammatory response correlated with increased production of proinflammatory cytokines and chemokines in both the bladder and the kidneys. Finally, we observed that the putative S. saprophyticus virulence factors Ssp and SdrI were important for persistence, but not for initial colonization, in the murine urinary tract. Thus, we characterized both host and bacterial factors involved in progression of S. saprophyticus UTI, and we describe a useful model system for studying factors involved in the pathogenesis of this Gram-positive uropathogen.