Role of EspFU protein in atypical enteropathogenic Escherichia coli.

Atypical enteropathogenic Escherichia coli (aEPEC) is one of the most important pathogen causing diarrhea disease worldwide. The hallmark of aEPEC pathogenesis is the ability to cause attaching and effacing (A/E) lesions on intestinal epithelium, a property triggered by proteins encoded on a pathogenicity island called locus of enterocyte effacement (LEE). While some aEPEC require tyrosine phosphorylation (Y-P) of Tir to trigger actin assembling, certain strains whose Tir is not tyrosine phosphorylated utilize the T3SS effector Tir-cytoskeleton coupling protein (TccP/TccP2) for efficient actin polymerization. In the present study, we evaluated the prevalence, production, and functions played by the EspFU protein on important aspects of aEPEC pathogenesis, such as interaction with epithelial cells and intestinal colonization. The tccP and/or tccP2 genes were detected in 45.8% of the aEPEC strains, with a predominance of tccP2 allele. Most of these strains carried tirY-P, suggesting that can trigger actin polymerization using both Tir tyrosine phosphorylation and TccP/TccP2 pathways. aEPEC strains carrying tccP or tccP2 were significantly associated to phylogroups E and B1, respectively. We also observed a differential production of TccP/TccP2 among the strains, regardless genotypes and phylogeny. Deletion of espFU from aEPEC BA320 (serotype O55:H7) significantly decreased bacterial adherence and impaired the ability to induce actin rearrangement in HeLa cells after 6 h of infection. Also, the espFU mutant showed lower colonization levels compared to the wild-type strain in a murine infection model. Analysis of the kinetics of pedestal formation showed EspFU-expressing strains were more adherent and induced actin rearrangement more rapidly than Tir-phosphorylated (TirY-P) producing aEPEC. Importantly, bacterial adherence and pedestal formation driven by EspFU downregulated the LEE expression, and also induced changes in the epithelial transcriptional response, specifically by activating pro-inflammatory genes such as NKFB, IL6 and IL8. In summary, our data suggest that EspFU protein is widely and phylogenetically distributed among aEPEC strains, and play an important role on bacterial attachment and intestinal colonization. Moreover, aEPEC could induce inflammation in a EspFU-dependent manner. (AU)