Evaluation of biofilm-forming capabilities of urinary Escherichia coli isolates in microtiter plate using two different culture media

Abstract

The ability of uropathogenic <em>E. coli</em> (UPEC) to cause symptomatic UTI is associated with the expression of a variety of virulence factors. Biofilm formation enables UPEC to resist the flow of urine and increases its tolerance to antimicrobials and the host immune response. The measurement of biofilm formation in vitro is affected by the type of culture medium used. The aim of this study was to evaluate biofilm-formation capabilities of UPEC in microtiter plate using two different culture media. A total of 170 isolates of <em>E. coli</em> were isolated from patients with symptomatic UTI in Gorgan, north of Iran. Biofilm formation of the strains was examined in LB and BHI broth with the addition of 1% sucrose. The quantitative analysis of biofilm formation was performed using crystal violet staining followed by spectrophotometry measurement after addition of decoloring solution. The biofilm formation of UPEC isolates in LB broth (20 isolates; 11.8%) was significantly (p <0.001) lower than those grown in BHI broth (105 isolates; 61.8%). All isolates that formed biofilm in LB broth also formed biofilm in BHI broth. Whilst 36 (21.2%) isolates grown in BHI broth formed strong biofilm, only one (0.6%) isolate grown in LB broth exhibited a similar result (P<0.007). Our data suggest that the process of biofilm formation by UPEC is strongly modulated by culture conditions and the method employed. In our study the use of BHI broth supplemented with 1% sucrose proved to be superior to the LB broth and can be employed for measurement of biofilm formation in UPEC.