Biofilm formation by Escherichia coli isolated from patients with urinary tract infections.

Aims: The significance of biofilm formation for the clinical picture of urinary tract infections (UTI) is largely unknown. We wanted to find out whether Escherichia coli (E. coli) strains isolated from UTI patients differ in their ability to form biofilms and whether this ability is associated with the clinical presentation of UTI.
Material and Methods: 70 E. coli strains were isolated from patients with cystitis (43 strains), pyelonephritis (11 strains) and urosepsis (16 strains) and biofilm formation was assessed on polystyrene microtiter plates by measuring the optical density (OD) of the attached material after 72 h of incubation and crystal violet staining of the bacteria. The formation of organized biofilm structures and the viability of the attached bacteria were verified by scanning electron microscopy and confocal scanning laser microscopy in a subsample of 22 strains.
Results: 31% of the E. coli strains formed a biofilm. The strains isolated from patients with pyelonephritis had higher ODs than those from patients with cystitis (difference of the means 0.19, 95% confidence limits (CL) 0.06 - 0.32, p = 0.02). The E. coli strains susceptible to antibiotics had higher ODs than the resistant strains (difference of the means 0.21, 95% CL 0.03 - 0.27, p = 0.016).
Conclusions: The ability of bacteria to persist and grow in a biofilm seems to be one of the important factors in both the resistance to antibiotics and the severity of urinary tract inflammation.