Abstract
Urinary tracts infection (UTI) caused by uropathogenic Escherichia coli (UPEC) is a common infectious disease. With the shortage of new antimicrobial agents, the increase in UPEC resistance to commonly used drugs, such as fluoroquinolones and β-lactams including carbapenems is a critical issue. UPEC invades urinary tract cells, where it aggregates, and subsequently, forms biofilm-like multicellular colonies termed intracellular bacterial communities (IBCs). This process allows the bacteria to establish infections and so may be a good potential target for new drugs to treat infections. Here, we show that deletion of the tolB gene, encoding a protein of the Tol-Pal system that was originally characterized as a protein complex for colicin uptake and maintenance of the outer membrane, decreases the level of bacterial internalization into and aggregation within cultured bladder epithelial cells and also inhibits the colonization of mice urinary tracts. The tolB mutant also exhibited defective motility because of impaired flagellum syntheses. The fliC and motA mutants, which are non-motile strains, also exhibited lower levels of bacterial internalization and aggregation than their wild-type parent. Additional deletion of tolB in the fliC mutant did not further decrease these, suggesting that the attenuated virulence of the tolB mutant is a result of defective motility. The tolA, tolQ, tolR, and pal mutants that lack other members of the Tol-Pal system also exhibited lower levels of motility and aggregation within bladder epithelial cells compared to their wild-type parent. These combined results suggest another role of the Tol-Pal system, i.e., that it is responsible for optimal internalization, aggregation followed by IBC formation within urinary tract cells, and bacterial motility.
Highlights
Urinary tract infection (UTI) is one of the most common infectious diseases
We identified a clone in a transposon library that we constructed in our previous work, that had a transposon inserted into its tolB gene and that exhibited a lower degree of attachment to 96-well polystyrene plates than the wild-type parent when cultured in LB medium
The tolB gene contributes to survival within macrophages and fatal infection of mice by Salmonella enterica serovar Typhimurium and the rot of plant leaves by the plant pathogen, Erwinia chrysanthemi while the pal gene and its product in E. coli and Haemophilus ducreyi aid in the induction of inflammation resulting in death by sepsis in mice, and pustule formation in humans, respectively (Bowe et al, 1998; Fortney et al, 2000; Hellman et al, 2002; Dubuisson et al, 2005)
Summary
When UPEC initially enters a urinary tract, the bacteria adhere to and invade the host bladder epithelial cells, where they aggregate and form biofilm-like multicellular microbial colonies termed intracellular bacterial communities (IBCs). Bacterial adherence to, internalization into and aggregation within bladder epithelial cells followed by IBCs formation are key processes in determining whether infection becomes refractory to treatment. Type 1 fimbriae are encoded by fim genes and are major fimbriae of this bacterium. They are required for initial attachment to and internalization into bladder epithelial cells, while motility contributes to bacterial fitness and migration to infection sites as the bacteria colonize the bladder (Martinez et al, 2000; Lane et al, 2005; Wright et al, 2005; Wright et al, 2007)
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