Abstract
BackgroundBiofilm formation by enteropathogenic Escherichia coli (EPEC) have been recently described in the prototype typical EPEC E2348/69 strain and in an atypical EPEC O55:H7 strain. In this study, we sought to evaluate biofilm formation in a collection of 126 atypical EPEC strains isolated from 92 diarrheic and 34 nondiarrheic children, belonging to different serotypes. The association of biofilm formation and adhesin-related genes were also investigated.ResultsBiofilm formation occurred in 37 (29%) strains of different serotypes, when the assays were performed at 26°C and 37°C for 24 h. Among these, four strains (A79, A87, A88, and A111) formed a stronger biofilm than did the others. The frequency of biofilm producers was higher among isolates from patients compared with isolates from controls (34.8% vs 14.7%; P = 0.029). An association was found between biofilm formation and expression of type 1 fimbriae and curli (P < 0.05). Unlike the previously described aEPEC O55:H7, one aEPEC O119:HND strain (A111) formed a strong biofilm and pellicle at the air-liquid interface, but did not express curli. Transposon mutagenesis was used to identify biofilm-deficient mutants. Transposon insertion sequences of six mutants revealed similarity with type 1 fimbriae (fimC, fimD, and fimH), diguanylate cyclase, ATP synthase F1, beta subunit (atpD), and the uncharacterized YjiC protein. All these mutants were deficient in biofilm formation ability.ConclusionThis study showed that the ability to adhere to abiotic surfaces and form biofilm is present in an array of aEPEC strains. Moreover, it seems that the ability to form biofilms is associated with the presence of type 1 fimbriae and diguanylate cyclase. Characterization of additional biofilm formation mutants may reveal other mechanisms involved in biofilm formation and bring new insights into aEPEC adhesion and pathogenesis.
Highlights
Biofilm formation by enteropathogenic Escherichia coli (EPEC) have been recently described in the prototype typical EPEC E2348/69 strain and in an atypical EPEC O55:H7 strain
A total of 126 EPEC strains isolated from 92 children with diarrhea and 34 asymptomatic controls were examined for the capacity of biofilm formation
This study showed that the ability to adhere to abiotic surfaces and form biofilm at low temperature is present in an array of atypical” EPEC (aEPEC) strains, and not restricted to a particular set of serotypes
Summary
Biofilm formation by enteropathogenic Escherichia coli (EPEC) have been recently described in the prototype typical EPEC E2348/69 strain and in an atypical EPEC O55:H7 strain. A key characteristic of EPEC strains is the ability to intimately attach to intestinal epithelial cells and form attaching and effacing (AE) lesions. These lesions are characterized by the destruction of the microvilli and the rearrangement of the cytoskeleton, culminating in a pedestal-like structure at the site of bacterial contact [7]. The AE genes are localized to the locus for enterocyte effacement (LEE) and encode intimin, a type III secretion system, secreted proteins (Esp) and the translocated intimin receptor [8,9,10] Another EPEC characteristic is the formation of microcolonies on cell monolayers “in vitro”, a pattern known as localized adherence (LA) [11]. EPEC forms microcolonies on cultured epithelial cells, cultures of pediatric small intestinal tissue, and biopsy samples from EPEC patients [12,13]
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