Development of a Vaccine against Escherichia coli Urinary Tract Infections

Abstract

Urinary tract infection (UTI) is the second most common infection in humans after those involving the respiratory tract. This results not only in huge annual economic costs, but in decreased workforce productivity and high patient morbidity. Most infections are caused by uropathogenic Escherichia coli (UPEC). Antibiotic treatment is generally effective for eradication of the infecting strain; however, documentation of increasing antibiotic resistance, allergic reaction to certain pharmaceuticals, alteration of normal gut flora, and failure to prevent recurrent infections represent significant barriers to treatment. As a result, approaches to prevent UTI such as vaccination represent a gap that must be addressed. Our laboratory has made progress toward development of a preventive vaccine against UPEC. The long-term research goal is to prevent UTIs in women with recurrent UTIs. Our objective has been to identify the optimal combination of protective antigens for inclusion in an effective UTI vaccine, optimal adjuvant, optimal dose, and optimal route of delivery. We hypothesized that a multi-subunit vaccine elicits antibody that protects against experimental challenge with UPEC strains. We have systematically identified four antigens that can individually protect experimentally infected mice from colonization of the bladder and/or kidneys by UPEC when administered intranasally with cholera toxin (CT) as an adjuvant. To advance the vaccine for utility in humans, we will group the individual antigens, all associated with iron acquisition (IreA, Hma, IutA, FyuA), into an effective combination to establish a multi-subunit vaccine. We demonstrated for all four vaccine antigens that antigen-specific serum IgG represents a strong correlate of protection in vaccinated mice. High antibody titers correlate with low colony forming units (CFUs) of UPEC following transurethral challenge of vaccinated mice. However, the contribution of cell-mediated immunity cannot be ruled out and must be investigated experimentally. We have demonstrated that antibodies bind to the surface of UPEC expressing the antigens. Sera from women with and without histories of UTI have been tested for antibody levels to vaccine antigens. Our results validate iron acquisition as a target for vaccination against UTI.

Keywords: E. coli; antibody response; urinary tract infection; vaccine.

Figure 1

High levels of in vivo expression of UPEC iron acquisition genes. E. coli isolates were collected from the urine of eight women with active UTI. Heat map indicates normalized microarray signal intensities for genes encoding UPEC iron acquisition systems. For reference, the overall most (rpsK, +) and least (pheM, −) expressed genes are shown in the bottom panels, representing average signal intensities of 15.82 and 3.88, respectively [26].

Figure 2

CBA/J mice were intranasally vaccinated with a primary dose of 100 µg purified protein crosslinked to 10 µg CT followed by two booster vaccinations with 25 µg protein. One week following the final boost, animals were transurethrally challenged with 1 × 10⁸ CFU of E. coli CFT073 or 536 and colonization was measured 48 h after challenge. Red bar is median value.

Figure 3

Correlation between vaccine-specific serum IgG titers and reduced bacterial counts in mice immunized with FyuA. Kidney CFUs from immunized and E. coli-challenged mice are plotted against their respective vaccine-specific serum IgG levels as measured by indirect ELISA, where absorbance at 450 nm reflects the relative quantity of vaccine-specific serum IgG. Dotted line indicates the limit of detection (100 CFU/g kidney tissue) for the immunization assay.