Roles of Putative Type II Secretion and Type IV Pilus Systems in the Virulence of Uropathogenic Escherichia coli

Ritwij Kulkarni,E Susan Slechta,Bijaya K Dhakal,Zachary Kurtz,David G Thanassi,Matthew A Mulvey,Dagmar Beier

doi:10.1371/journal.pone.0004752

Abstract

BackgroundType II secretion systems (T2SS) and the evolutionarily related type IV pili (T4P) are important virulence determinants in many Gram-negative bacterial pathogens. However, the roles of T2SS and T4P in the virulence of extraintestinal pathogenic Escherichia coli have not been determined.Methodology/Principal FindingsTo investigate the functions of putative T2SS and T4P gene clusters present in the model uropathogenic E. coli (UPEC) strains UTI89 and CFT073, we deleted the secretin gene present in each cluster. The secretin forms a channel in the outer membrane that is essential for the function of T2S and T4P systems. We compared the secretin deletion mutants with their wild type counterparts using tissue culture assays and the CBA/J mouse model of ascending urinary tract infection. No deficiencies were observed with any of the mutants in adherence, invasion or replication in human bladder or kidney cell lines, but UTI89 ΔhofQ and UTI89 ΔgspD exhibited approximately 2-fold defects in fluxing out of bladder epithelial cells. In the mouse infection model, each of the knockout mutants was able to establish successful infections in the bladder and kidneys by day one post-infection. However, UTI89 ΔhofQ and a CFT073 ΔhofQ ΔyheF double mutant both exhibited defects in colonizing the kidneys by day seven post-infection.Conclusions/SignificanceBased on our results, we propose that the putative T4P and T2S systems are virulence determinants of UPEC important for persistence in the urinary tract, particularly in renal tissues.

Highlights

Escherichia coli are a diverse group of Gram-negative bacteria that can be divided into three major subgroups: commensals in the intestinal tract of warm-blooded mammals, agents of intestinal infections such as hemmorhagic colitis and hemolytic-uremic syndrome, and extra-intestinal pathogenic E. coli (ExPEC) [1]
T2SS and T4P gene clusters in CFT073 and UTI89 uropathogenic E. coli (UPEC) strain CFT073 is a well characterized strain isolated from the blood of a woman suffering from pyelonephritis [35], whereas UTI89 is a UPEC strain isolated from a cystitis patient [36]
We begin to address this question by constructing deletion mutations to disable putative T2SS and T4P gene clusters present in the genomes of the model UPEC strains UTI89 and CFT073

Summary

Introduction

Escherichia coli are a diverse group of Gram-negative bacteria that can be divided into three major subgroups: commensals in the intestinal tract of warm-blooded mammals, agents of intestinal infections such as hemmorhagic colitis and hemolytic-uremic syndrome, and extra-intestinal pathogenic E. coli (ExPEC) [1]. ExPEC are causative agents of a range of diseases, including urinary tract infections (UTIs), nosocomial pneumonia, neonatal meningitis, and neonatal sepsis. The success of UPEC as pathogens can be attributed to their panoply of virulence factors These include a variety of toxins, such as cytotoxic and necrotizing factor 1 (CNF1), hemolysin (hlyA), and secreted autotransporter toxin (Sat), and a diverse range of adhesins, including type 1 and P pili. The adhesins present at the tips of type 1 and P pili, FimH and PapG, respectively, aid UPEC in adhering to the bladder and kidney epithelial cells of the host [9,10]. A variety of structurally and functionally different virulence factors work to aid the pathogenesis of UPEC in the host urinary tract. The roles of T2SS and T4P in the virulence of extraintestinal pathogenic Escherichia coli have not been determined

Methods

Results

Conclusion