Resumo

The ability of 154 atypical enteropathogenic Escherichia coli strains isolated from children with or without diarrhea to form biofilm on polystyrene plates was studied. The presence and the expression of adhesins associated with biofilm formation were also examined. Biofilm production was assessed in 96-well microtiter plates at 26oC or 37oC for 24 h using three different media, namely, Luri-Bertani (LB), LB without salt (LBNS), and Dulbecco´s modified Eagle´s medium (DMEM. Expression of type 1 fimbriae was examined by mannose-sensitive hemagglutination (MSHA) assay. Curli expression was assessed on Congo red agar plates. The presence of adhesin-related gene sequences was determined by PCR. Biofilm formation occurred in 38 (24.7%) atypical EPEC strains belonging to EPEC and non-EPEC serogroups, when the assays were performed at 26oC or 37oC for 24 h. Thirteen strains were classified as strong biofilm producers and the remaining 25 strains were classified as weak biofilm producers. The fimH sequence was present in 28 (73.7%) strains, but only 20 of those expressed type 1 fimbriae as detected by mannose-sensitive hemagglutination(MSHA) assay. The gene sequences related to curli (csgA and crl) were identified in 12 (31.6%) strains, and 8 of these strains expressed curli as evidenced by characteristic red-colored colonies formed on Congo red agar plates. The gene sequences related to the autotransporter proteins AIDA-I, Ag43, Cah, Eha, and Sab occurred in 9 (23.7%), 10 (26.3%), 5 (13.1%), 3 (7.9%), and 6 (15.8%), respectively. In conclusion, this is the first study investigating biofilm formation in a large collection of atypical EPEC strains, and this ability seems to be associated with the presence of different factors such as type I fimbria, curli, and autotransporter proteins. Fapesp