RESUMO
E. coli is implicated in many biomaterial related infections. Typically, these infections are associated with biofilm formation. Cells in biofilm display phenotypic traits that are dramatically different from those of their free-floating planktonic counterparts and are more resistant to antimicrobial agents. Consequently, biofilm - related infections are inherently challenging to treat and difficult to fully eradicate with normal treatment regimens. The aim of this work is to study E. coli biofilm formation and antimicrobial susceptibility of biofilm forming strains in the planktonic and biofilm states by broth and agar dilution methods according to NCCLs. Out of 102 catheterized patient's urine samples and 58 mid-stream urine samples, 91 [56.9%] E. coli strains were isolated, 46 of them [50.5%] were capable to form biofilm by Congo-red method and 43 [47.3%] were positive biofilm producers according to the quantitative spectrophotometric assay. Most biofilm producing strains were isolated from catheterized patients [67.6%]. No significant agreement was found between E. coli planktonic and biofilm positive isolates pertaining to their antimicrobial susceptibility. There was also a clear difference in antibiotic susceptibility seen between planktonic and biofilm populations of the same strain in both MIC50 and MIC90 which were in planktonic isolates much lower than those required to inhibit positive biofilm producers. In conclusion, this study indicated that there was a significant percentage of E. coli able to grow within biofilm, especially strains isolated from catheterized patients. E. coli biofilm positive strains were highly resistant to the antimicrobials in comparison to their planktonic counterparts. Accordingly, specimens collected from catheters should be tested for antibiotic susceptibility by special methods. Also, modification of the biomaterial surface to reduce biofilm formation or irrigation with antiseptic and antiadhesive materials is highly recommended