Purpose The
treatment of
urinary tract infections (UTI) with
antibiotics is commonly used, but
recurrence and
antibiotic resistance have been growing and concerning clinicians. We studied whether the rapid onset of a protective
biofilm may be responsible for the lack of
effectiveness of
antibiotics against selected
bacteria . Materials and
Methods Two established
uropathogenic Escherichia coli strains , UTI89 and CFT073, and two
Pseudomonas aeruginosa strains , PA01 and
Boston -41501, were studied to establish a reliable
biofilm formation process.
Bacterial growth (BG) was determined by optical density at 600 nm (OD 600) using a spectrophotometer, while
biofilm formation (BF) using
crystal violet staining was measured at OD 550. Next, these bacterial
strains were treated with clinically relevant
antibiotics ,
ciprofloxacin HCl (200 ng/mL and 2 μg/mL),
nitrofurantoin (20 μg/mL and 40 μg/mL) and
ampicillin (50 μg/mL) at
time points of 0 (T0) or after 6 hours of
culture (T6). All measurements, including controls (
bacteria -1%
DMSO ), were done in triplicates and repeated three times for consistency. Results The tested
antibiotics effectively inhibited both BG and BF when administered at T0 for UPEC
strains , but not when the
antibiotic administration started 6 hours later. For
Pseudomonas strains , only
Ciprofloxacin was able to significantly inhibit
bacterial growth at T0 but only at the higher concentration of 2 μg/mL for T6. Conclusion When established UPEC and
Pseudomonas bacteria were allowed to
culture for 6 hours before initialization of
treatment , the
therapeutic effect of selected
antibiotics was greatly suppressed when compared to immediate
treatment , probably as a result of the protective
nature of the
biofilm . .