The aggregate-forming pili (AFP) mediates the aggregative adherence of a hybrid-pathogenic Escherichia coli (UPEC/EAEC) isolated from a urinary tract infection

Abstract

Enteroaggregative Escherichia coli (EAEC) comprises an important diarrheagenic pathotype, while uropathogenic E. coli (UPEC) is the most important agent of urinary tract infection (UTI). Recently, EAEC virulence factors have been detected in E. coli strains causing UTI, showing the importance of these hybrid-pathogenic strains. Previously, we detected an E. coli strain isolated from UTI (UPEC-46) presenting characteristics of EAEC, e.g ., the aggregative adherence (AA) pattern and EAEC-associated genes ( aatA, aap , and pet ). In this current study, we analyzed the whole genomic sequence of UPEC-46 and characterized some phenotypic traits. The AA phenotype was observed in cell lineages of urinary and intestinal origin. The production of curli, cellulose, bacteriocins, and Pet toxin was detected. Additionally, UPEC-46 was not capable of forming biofilm using different culture media and human urine. The genome sequence analysis showed that this strain belongs to serotype O166:H12, ST10, and phylogroup A, harbors the tet, aadA , and dfrA / sul resistance genes, and is phylogenetically more related to EAEC strains isolated from human feces. UPEC-46 harbors three plasmids. Plasmid p46-1 (~135 kb) carries some EAEC marker genes and those encoding the aggregate-forming pili (AFP) and its regulator ( afpR ). A mutation in afpA (encoding the AFP major pilin) led to the loss of pilin production and assembly, and notably, a strongly reduced adhesion to epithelial cells. In summary, the genetic background and phenotypic traits analyzed suggest that UPEC-46 is a hybrid strain (UPEC/EAEC) and highlights the importance of AFP adhesin in the adherence to colorectal and bladder cell lines.

Role of aggregate-forming pilus (AFP) in adherence and colonization of both intestinal and urinary tracts

“…Adherence assays were performed according to Schüroff et al [ 7 ], using different human cells lines: cervical carcinoma (HeLa; ATCC CCL-2), colorectal adenocarcinoma (HT-29; ATCC HTB-38), and urinary bladder carcinoma (5637; ATCC HTB-9).…”

“…In a recent study, we described the geno- and phenotypic characteristics of one E. coli strain (UPEC-46) isolated from a case of UTI [ 7 ]. This strain was classified as a hybrid-pathogenic UPEC/EAEC, as it was isolated from an extraintestinal infection, harboured EAEC virulence markers and was phylogenetically associated to EAEC strains [ 7 ]. Moreover, the aggregate-forming pili (AFP) were essential for establishing the AA pattern expressed by this strain in different cell lines [ 7 ].…”

“…AFP was initially described in a Shiga-toxigenic E. coli (STEC)/EAEC strain as a type IV pilus sharing a similar genetic organization with the bundle-forming pilus (BFP) present in enteropathogenic E. coli (EPEC) [ 10 ]. Following the first description, AFP-encoding genes were also found in EAEC strains isolated from healthy subjects and patients with diarrhea [ 7 , 11 ]. The ultrastructure of AFP was observed by transmission electron microscopy (TEM) using a specific anti-AFP serum, and it differed from BFP, presenting fimbrial structures not assembled in bundles [ 7 ].…”

“…Following the first description, AFP-encoding genes were also found in EAEC strains isolated from healthy subjects and patients with diarrhea [ 7 , 11 ]. The ultrastructure of AFP was observed by transmission electron microscopy (TEM) using a specific anti-AFP serum, and it differed from BFP, presenting fimbrial structures not assembled in bundles [ 7 ]. AFP has also been associated with bacterial autoaggregation, adherence to bladder and colorectal epithelial cells and cytotoxicity towards epithelial cells in stx -positive E. coli [ 7 , 10 ].…”

“…The ultrastructure of AFP was observed by transmission electron microscopy (TEM) using a specific anti-AFP serum, and it differed from BFP, presenting fimbrial structures not assembled in bundles [ 7 ]. AFP has also been associated with bacterial autoaggregation, adherence to bladder and colorectal epithelial cells and cytotoxicity towards epithelial cells in stx -positive E. coli [ 7 , 10 ]. However, the role of AFP in intestinal colonization and uropathogenesis remains unclear.…”