The Periplasmic Trehalase Affects Type 1 Fimbria Production and Virulence of Extraintestinal PathogenicEscherichia coliStrain MT78

ABSTRACTExtraintestinal pathogenicEscherichia coli(ExPEC) is responsible for various infections outside the gastrointestinal tract in humans and other animals. ExPEC strain MT78 is invasive to various nonphagocytic cells and highly virulentin vivo. To identify genes required for invasion of nonphagocytic cells by this strain, we applied signature-tagged mutagenesis to generate a library of mutants and tested them for invasion of avian fibroblasts. Mutants showing reduced cellular invasion included those with insertions in thefimoperon, encoding type 1 fimbriae. Another attenuated mutant showed a disruption in thetreAgene, which encodes a periplasmic trehalase. The substrate of TreA, trehalose, can be metabolized and used as a carbon source or can serve as an osmoprotectant under conditions of osmotic stress inE. coliK-12. We generated and characterized mutant MT78ΔtreA. In contrast to the wild type, MT78ΔtreAwas able to grow under osmotic stress caused by 0.6 M urea but not in minimal M9 medium with trehalose as the only carbon source. It presented decreased association and invasion of avian fibroblasts, decreased yeast agglutination titer, and impaired type 1 fimbria production. In a murine model of urinary tract infection, MT78ΔtreAwas less able to colonize the bladder. All phenotypes were rescued in the complemented mutant. Our results show that thetreAgene is needed for optimal production of type 1 fimbriae in ExPEC strain MT78 and that loss oftreAsignificantly reduces its cell invasion capacity and colonization of the bladder in a murine model of urinary tract infection.

Genome Sequence of Avian Escherichia coli Strain IHIT25637, an Extraintestinal Pathogenic E. coli Strain of ST131 Encoding Colistin Resistance Determinant MCR-1

Sequence type 131 (ST131) is one of the predominant Escherichia coli lineages among extraintestinal pathogenic E. coli (ExPEC) that causes a variety of diseases in humans and animals and frequently shows multidrug resistance. Here, we report the first genome sequence of an ST131-ExPEC strain from poultry carrying the plasmid-encoded colistin resistance gene mcr-1 .

TolC Promotes ExPEC Biofilm Formation and Curli Production in Response to Medium Osmolarity

While a high osmolarity medium activates Cpx signaling and causes CpxR to represscsgDexpression, and efflux protein TolC protein plays an important role in biofilm formation inEscherichia coli,whether TolC also responds to an osmolarity change to regulate biofilm formation in extraintestinal pathogenicE. coli(ExPEC) remains unknown. In this study, we constructedΔtolCmutant and complement ExPEC strains to investigate the role of TolC in the retention of biofilm formation and curli production capability under different osmotic conditions. TheΔtolCmutant showed significantly decreased biofilm formation and lost the ability to produce curli fimbriae compared to its parent ExPEC strain PPECC42 when cultured in M9 medium or 1/2 M9 medium of increased osmolarity with NaCl or sucrose at 28°C. However, biofilm formation and curli production levels were restored to wild-type levels in theΔtolCmutant in 1/2 M9 medium. We propose for the first time that TolC protein is able to form biofilm even under high osmotic stress. Our findings reveal an interplay between the role of TolC in ExPEC biofilm formation and the osmolarity of the surrounding environment, thus providing guidance for the development of a treatment for ExPEC biofilm formation.