The shf Gene of a Shigella flexneri Homologue on the Virulent Plasmid pAA2 of Enteroaggregative Escherichia coli 042 Is Required for Firm Biofilm Formation

Abstract

Enteroaggregative Escherichia coli (EAEC) is an increasingly important cause of diarrhea in both developing and industrialized countries, and is characterized by strong biofilm formation on the intestinal mucosa. Sequencing of the virulent plasmid pAA2 of the prototype EAEC 042 revealed a cluster of three open reading frames (ORFs; shf, capU, and virK) ca. 93% identical to a similar cluster located in Shigella flexneri. The function of the first ORF Shf protein is not known, but the closest well-characterized homologue is the IcaB protein of Staphylococcus epidermidis, which plays a crucial role in exopolysaccharide modification in bacterial biofilm formation. To investigate the role of this cluster in the virulence of EAEC, we mutated three genes at this locus. All the mutants maintained the aggregative phenotype in the liquid phase. However, the insertional mutant of shf formed a less abundant biofilm in a microtiter plate assay than did the wild type, while the capU mutant and the virK mutant did not. The complementation of the shf mutant with this cluster restored the thick biofilm similar to that of the wild type. The shf transcriptional level decreased in the transcriptional regulator aggR mutant and was restored when the mutant was complemented with aggR. These results suggest that the shf gene is required for the firm biofilm formation of EAEC 042, and transcription of the shf gene is dependent on AggR.

The Heat-Resistant Agglutinin Family Includes a Novel Adhesin from Enteroaggregative Escherichia coli Strain 60A

“…To date, most studies of EAEC adherence have focused on structural adhesins known as aggregative adherence fimbriae. However, recent research has shown that EAEC strains also harbor an expanding repertoire of nonstructural outer membrane proteins that contribute to colonization (1,4,14,28).One such outer membrane protein is heat-resistant agglutinin 1 (Hra1), an accessory adhesin that we recently characterized in EAEC strain 042 (1). The hra1 gene (along with its 90% identical allelic variant hek, reported from uropathogenic E. coli and neonatal meningitic E. coli [11,39]) is predicted to encode a 29-kDa precursor, which is processed to a 25-kDa outer membrane protein.…”

“…To date, most studies of EAEC adherence have focused on structural adhesins known as aggregative adherence fimbriae. However, recent research has shown that EAEC strains also harbor an expanding repertoire of nonstructural outer membrane proteins that contribute to colonization (1,4,14,28).…”

Public health risks associated with Enteroaggregative Escherichia coli (EAEC) as a food‐borne pathogen

“…Other studies suggest that the Shf protein-encoding gene (shf) is required for strong biofilm formation of EAEC serotype O42, and that transcription of the shf gene is dependent on AggR (Fujiyama et al, 2008). There is considerable heterogeneity in putative virulence genes of EAEC isolates from diarrhoeic children in India and biofilm formation appears to be associated with multiple genes (Wani et al, 2012).…”

Caracterização da proteína dispersina em amostras de Escherichia coli não pertencentes ao patótipo de E. coli enteroagregativa.

“…Tais genes codificam a toxina termoestável EAST-1, a proteína Shf, envolvida na formação de biofilme, o usher da fímbria AAF/III e uma proteína envolvida na biossíntese de yersiniabactina, respectivamente (BERNIER et al, 2003;CZECZULIN et al, 1999;FUJIYAMA et al, 2008;SAVARINO et al, 1993).…”

“…Monteiro-Neto et al (2003) descreveram uma proteína de 58 kDa (Ap58) que, na amostra 236 do sorotipo O111:H12, apresentava as mesmas funções descritas por Debroy et al (1995). O gene que codifica a Ap58 foi localizado no cromossomo da amostra protótipo (MONTEIRO-NETO et al, 2003).No plasmídeo pAA, também estão localizados os genes aggR, que codifica um regulador de virulência (NATARO et al, 1994), pet, que codifica uma enterotoxina autotransportadora (ESLAVA et al, 1998), shf, envolvido na formação de biofilme em EAEC 042 (FUJIYAMA et al, 2008) e aatA, que codifica uma proteína de membrana externa que faz parte de um complexo transportador de proteínas (NISHI et al, 2003). O fragmento sonda EAEC (CVD432) desenvolvido por Baudry et al (1990), corresponde a uma porção deste último gene.…”