RESUMEN
AIM: The presented study was to compare in vitro biofilm production by bacterial strains from chronic/recurrent and from acute non-complicated UTIs. The activity of gentamicin and colistin on biofilm form of these strains has also been detected, with goal to predict the gentamicin and colistin therapeutic efficacy in the antimicrobial treatment of patients with a suspected presence of biofilm in urinary tract. MATERIAL AND METHODS: The group of 40 bacterial strains repeatedly isolated from patients with chronic or recurrent UTIs was compared with the group of 40 strains from acute UTIs. Both groups contained comparable number of strains of Escherichia coli, Klebsiella spp., Proteus mirabilis and Pseudomonas aeruginosa. Biofilm production was assessed by method in polystyrene microtiter plate. The MIC and MBC values of gentamicin and colistin were detected by broth microdilution assay. The minimal biofilm inhibitory (MBIC) and biofilm eradication concentrations (MBEC) were tested by microdilution method. Non-inactivated biofilm-associated bacteria were detected after overnight incubation in broth medium free of antimicrobials. The statistical analysis of results was performed by Fisher's exact test and by Student's t-test. RESULTS: Biofilm was produced by 90% strains from chronic UTIs, but only by 52% of strains from acute UTIs (p = 0.0004). In the biofilm producing strains, the MBIC values of gentamicin reached from four to 256 mg/L, the MBIC levels of colistin from two to 64 mg/L. The minimal biofilm eradicating concentrations were even higher: for gentamicin from eight to > 512 mg/L, and for colistin from 32 to > 512 mg/L. The differences between MIC and MBIC/MBEC levels were statistically highly significant (p < 0.0001). Presumably, the therapeutic success of parenterally applied gentamicin or colistin on biofilm-related urinary tract infections would be, without respect to the high concentration of gentamicin or colistin achievable in urine during parenteral application, rather unpredictable. Local intravesical instillation would allow for achieving higher gentamicin and colistin concentrations; however, there is need for interpretation criteria for MBEC values concerning therapy, as well as for clinical studies allowing for application of those values to predict clinical success of therapy. CONCLUSIONS: Laboratory detection of biofilm production and evaluation of the MBIC/MBEC values of antimicrobials for strains producing biofilm might be a valuable complement to the microbiologic diagnostics of chronic and recurrent UTIs. It might provide valuable information for more reliable individualised therapy and so decrease the risk of emergence and selection of multiresistant strains during repeated and non-eradicating therapy of chronic and recurrent UTIs.