Background and purpose: Staphylococcus saprophyticus is a frequent cause of both uncomplicated and complicated urinary tract infections (UTI) in young females and has recently been established as the most prominent gram-positive uropathogen. Although the effects of subinhibitory concentrations of antimicrobials on numerous other pathogenic bacteria have been studied, little is known regarding how S saprophyticus responds under such conditions.
Materials and methods: In this study, we investigated the effects of subminimum inhibitory concentrations (MIC) of ciprofloxacin (CIP) on S saprophyticus attachment to glass microscope slides, ureteral stent material, and T24 bladder cells, as well as its effects on S saprophyticus-induced proinflammatory cytokine expression in bladder cells.
Results: Adherence to glass microscope slides, ureteral stent material, and bladder cell monolayers were all significantly increased in the presence of sub-MIC levels of CIP. While the S saprophyticus challenge of T24 bladder cell monolayers significantly upregulated both interleukin (IL)-6 and IL-8 expression, sub-MIC CIP abrogated these effects, returning their secretion to control levels.
Conclusions: Our results demonstrate that exposure to sub-MIC CIP increases S saprophyticus adherence to both abiotic and biotic surfaces including urinary device material and cultured bladder cells. In addition, low levels of this antimicrobial downregulate S saprophyticus-stimulated proinflammatory cytokine secretion in the bladder. These changes may make S saprophyticus more effective at colonizing the urinary tract and highlights the need for clinicians to consider the impact of subinhibitory concentrations of antimicrobials on bacteria when designing treatment strategies to manage UTI.