Filamentation by Escherichia coli subverts innate defenses during urinary tract infection - PubMed (original) (raw)

Filamentation by Escherichia coli subverts innate defenses during urinary tract infection

Sheryl S Justice et al. Proc Natl Acad Sci U S A. 2006.

Abstract

To establish disease, an infecting organism must overcome a vast array of host defenses. During cystitis, uropathogenic Escherichia coli (UPEC) subvert innate defenses by invading superficial umbrella cells and rapidly increasing in numbers to form intracellular bacterial communities (IBCs). In the late stages of the IBC pathway, filamentous and bacillary UPEC detach from the biofilm-like IBC, fluxing out of this safe haven to colonize the surrounding epithelium and initiate subsequent generations of IBCs, and eventually they establish a quiescent intracellular reservoir. Filamentous UPEC are not observed during acute infection in mice lacking functional Toll-like receptor 4 (TLR4), suggesting that the filamentous phenotype arises in response to host innate immunity. We investigated SulA, a cell division inhibitor associated with the SOS response, to gain insight into the role of filamentous UPEC in pathogenesis. A transcriptional reporter from P(sulA) revealed spatial and temporal differences in expression within IBCs, and it was active in the majority of filamentous UPEC. Although UTI89 and UTI89 DeltasulA both formed first-generation IBCs equally well, UTI89 DeltasulA was sharply attenuated in formation of second-generation IBCs and establishment of the quiescent intracellular reservoir. The virulence of UTI89 DeltasulA was restored in TLR4-deficient mice, suggesting that filamentation facilitates the transition to additional rounds of IBC formation by subverting innate immune responses. These findings demonstrate that transient SulA-mediated inhibition of cell division is essential for UPEC virulence in the murine model of cystitis.

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Conflict of interest statement

The authors declare no conflict of interest.

Figures

Fig. 1.

Microscopic examination of IBC formation and UPEC filamentation. Female 7- to 9-week old C3H/HeN (a_–_e) or C3H/HeJ (f) mouse strains were infected with 107 cfu of UTI89/pCOMGFP (a and c) or UTI89 Δ_sulA_/pCOMGFP (b, d, and f) or UTI89 (e; red) plus UTI89 Δ_sulA_/pCOMGFP (e; green) by transurethral catheterization. Bladders were harvested at 6 h (a and b), 16 h (e), or 24 h (c, d, and f) postinfection, and they were prepared as described in Materials and Methods for visualization by confocal laser scanning fluorescent microscopy with three-dimensional reconstruction or as an optical slice (d). (Scale bars: 30 μm.)

Fig. 2.

Virulence of UTI89 Δ_sulA_. Female C3H/HeN (a) or C3H/HeJ (b) mice were transurethrally inoculated with 107 UTI89 (◀), UTI89 Δ_sulA_ (▶), or UTI89 Δlon (♦). Bladders were harvested at 6 h, 16 h, 24 h, 48 h, or 2 weeks postinfection and homogenized, and viable bacteria were enumerated as cfu per bladder. Each graph is representative of three independent experiments. The statistical significance was assayed by using the Mann–Whitney test (ns, not significant; ∗, P = 0.03; ∗∗, P = 0.004; nd, not determined).

Fig. 3.

Expression of sulA in vivo. Female C3H/HeN (a_–_d) or C3H/HeJ (e and f) mice were transurethrally inoculated with 107 UTI89 attB::P_sulA_-gfp. Bladders were harvested at 4 h (a), 6 h (b), or 16 (c_–_f), and they were prepared as described in Materials and Methods for visualization by laser scanning fluorescent microscopy. They were visualized with three-dimensional reconstruction (a_–_d) or as an optical slice (e and f). (Scale bars: a, b, e, and f, 50 μm; c and d, 30 μm.)

Fig. 4.

PMN phagocytosis in vitro. Human and mouse PMNs were incubated with UTI89 under inducing conditions for 20 min, and they were visualized by using phase microscopy (a, b, e, and f) or fluorescent microscopy (c and d). (a) Opsonized, uninduced UTI89 with human PMNs. (b) Opsonized induced UTI89 P_lac_::sulA. (c and d) MMC-induced UTI89 with mouse PMNs. (e) Uninduced UTI89 with human PMNs. (f) MMC-induced UTI89 with human PMNs. (Scale bars: a_–_d, 30 μm; e and f, 50 μm.)

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Filamentation by Escherichia coli subverts innate defenses during urinary tract infection - PubMed (original) (raw)