# Uropathogenic Escherichia coli Biofilms: Antibiotic Pressure and Interaction with Human Neutrophils

## TL;DR

This study explores how antibiotics affect UPEC biofilm formation and their interaction with human neutrophils, revealing increased antibiotic resistance and harmful effects on immune cells.

## Contribution

The study reveals that sub-MICs of ciprofloxicol can stimulate UPEC biofilm growth and alter bacterial morphology.

## Key findings

- MBEC values were higher than MBC for all tested antibiotics, showing increased resistance in biofilms.
- Sub-MIC ciprofloxacin increased biofilm biomass and induced filamentous bacterial morphology.
- Biofilm-embedded bacteria reduced neutrophil viability mainly through necrosis.

## Abstract

Uropathogenic Escherichia coli (UPEC) is a primary cause of urinary tract infections (UTIs), with recurrent cases often linked to its ability to form biofilms. This study investigated the effects of various antibiotics on UPEC biofilm formation and the subsequent interaction of these biofilms/their supernatants with human neutrophils. We determined the minimum inhibitory concentrations (MIC), minimum bactericidal concentrations (MBC), and biofilm eradication concentrations (MBEC) for ampicillin, gentamicin, chloramphenicol, ciprofloxacin, and levofloxacin. Our results showed an increase in MBEC compared to MBC for all tested antibiotics, confirming the enhanced antibiotic resistance of bacteria in biofilm. We found that sub-MICs of ciprofloxacin, which moderately inhibited planktonic growth, actually stimulated an increase in biofilm biomass. This antibiotic-induced biofilm growth was accompanied by changes in bacterial morphology, including the formation of elongated, filamentous cells, an adaptive stress response. Biofilm-embedded bacteria, but not their supernatants, significantly reduced neutrophil viability, primarily by inducing neutrophil necrosis. The presence of ciprofloxacin during biofilm formation did not fundamentally alter interactions with neutrophils. These findings highlight the importance of studying effects of antibiotic pressure on biofilm formation, underscoring the challenges in antibiotic treatment of UTIs.