Roles of the ZnuACB and ZupT transporters were assessed in -and 48-fold reductions, respectively). In addition, in single-strain infection experiments, the ⌬znu and ⌬znu ⌬zupT mutants were reduced in the kidneys (P ‫؍‬ 0.0012 and P < 0.0001, respectively). Complementation of the CFT073 ⌬znu ⌬zupT mutant with the znuACB genes restored growth in Zn-deficient medium and bacterial numbers in the bladder and kidneys. The loss of the zinc transport systems decreased both motility and resistance to hydrogen peroxide, which could be restored by supplementation with zinc. Overall, the results indicate that Znu and ZupT are required for growth in zinc limited-conditions, that Znu is the predominant zinc transporter, and that the loss of Znu and ZupT has a cumulative effect on fitness during UTI, which may in part be due to reduced resistance to oxidative stress and motility.

Escherichia coli can cause extraintestinal infections in humans and animals. The hlyF gene is epidemiologically associated with virulent strains of avian pathogenic E. coli and human neonatal meningitis-associated E. coli. We demonstrated that culture supernatants of E. coli expressing HlyF induced autophagy in eukaryotic cells. This phenotype coincided with an enhanced production of outer membrane vesicles (OMVs) by bacteria expressing HlyF. The HlyF protein displays a predicted catalytic domain of the short-chain dehydrogenase/reductase superfamily. This conserved domain was involved the ability of HlyF to promote the production of OMVs. The increased production of OMVs was associated with the release of toxins. hlyF was shown to be expressed during extraintestinal infection and to play a role in the virulence of extraintestinal pathogenic E. coli in a chicken model of colibacillosis. This is the first evidence that pathogenic bacteria produce a virulence factor directly involved in the production of OMVs.

The pstSCAB-phoU operon encodes the phosphate-specific transport system (Pst). Loss of Pst constitutively activates the Pho regulon and decreases bacterial virulence. However, specific mechanisms underlying decreased bacterial virulence through inactivation of Pst are poorly understood. In uropathogenic Escherichia coli (UPEC) strain CFT073, inactivation of pst decreased urinary tract colonization in CBA/J mice. The pst mutant was deficient in production of type 1 fimbriae and showed decreased expression of the fimA structural gene which correlated with differential expression of the fimB, fimE, ipuA, and ipbA genes, encoding recombinases, mediating inversion of the fim promoter. The role of fim downregulation in attenuation of the pst mutant was confirmed using a fim phase-locked-on derivative, which demonstrated a significant gain in virulence. In addition, the pst mutant was less able to invade human bladder epithelial cells. Since type 1 fimbriae contribute to UPEC virulence by promoting colonization and invasion of bladder cells, the reduced bladder colonization by the pst mutant is predominantly attributed to downregulation of these fimbriae. Elucidation of mechanisms mediating the control of type 1 fimbriae through activation of the Pho regulon in UPEC may open new avenues for therapeutics or prophylactics against urinary tract infections. Pathogenic Escherichia coli comprises a diversity of strains associated with both intestinal and extraintestinal infections (39). Urinary tract infections (UTIs) are one of the most common bacterial infections, and uropathogenic E. coli (UPEC) is the predominant causal agent, representing up to 85% of communityacquired UTIs (28). In addition to causing UTIs, extraintestinal pathogenic E. coli (ExPEC) is an important pathogen associated with neonatal meningitis and septicemia in humans, as well as systemic infections in poultry and livestock (60, 61). Many virulence factors associated with UPEC strains are important for establishing infection, and these include adhesins, toxins, iron acquisition systems, and capsular antigens (53).An important aspect of bacterial virulence is the capacity to rapidly adapt to changes and stresses encountered during infection of the host, since changes in the host environment may serve as cues mediating regulation of expression of key virulence factors during infection (25,47). One of the mechanisms by which bacteria respond to environmental signals is through two-component signal transduction systems (TCSs). TCSs are composed of an inner-membrane histidine kinase sensor protein and cytoplasmic response regulator (81). TCSs are important for bacterial adaptation and virulence (6, 12), and a number of TCSs have been identified to be important for pathogenic E. coli, e.g., BarA-UvrY, PhoPQ, and QseBC (4, 31, 41, 56).The Pho regulon is controlled by the PhoBR TCS, in which PhoR is the sensor histidine kinase and PhoB the response regulator. PhoBR responds to phosphate limitation, i.e., when the extracellular phosphate concentration falls belo...