Urinary Tract Infections

Approximately half of all girls and women and some boys and men will experience at least one urinary tract infection (UTI) during their lifetime. UTI are the most common hospital-associated infection, and can lead to death in critically ill patients. Effective therapy is based on antibiotics, but bacterial resistance is an ongoing issue for management of UTI.

An unexpected source of antibiotic resistance among bacterial uropathogens may be the general stress response. This pathway is activated by a number of environmental stressors, including antibiotics, starvation, and disinfectants. In collaboration with A.C. Matin's laboratory, we are examining the in vivo mechanisms by which the general stress response imbues bacteria with resistance to specific antibiotics.

Below is video footage from our Journal of Visualized Experiments article on the mouse transurethral catetherization-based UTI model:

Note: If you are having trouble viewing the video please update your Flash Player. If this is not the problem, please visit the article on the JoVE website.

We are also interested in urinary tract co-infections, an understudied area of UTI biology. Urinary tract co-infections can be polymicrobial, in which more than one bacterial uropathogen have taken hold in host urinary tract tissues. Other urinary tract co-infections can be cross-kingdom, wherein eukaryotic uropathogens (i.e., Candida species or Schistosoma haematobium) have infected the same host urinary tracts as their bacterial brethren. In all of these settings, it is plausible that the interactions among multiple uropathogens and their hosts result in unique pathobiology.

For instance, numerous studies have observed that people with urogenital schistosomiasis (infection by Schistosoma haematobium worms) have higher rates of bacterial UTI than expected. It is unclear whether this purported association is a true biological link, or merely detection bias. The association between urogenital schistosomiasis and bacterial UTI susceptibility could be subject to detection bias; since people with S. haematobium infection often have urinary symptoms such as hematuria, they may come to urologic attention and undergo bacterial urine cultures more frequently than people without urogenital schistosomiasis.

Even if there is a true biological connection between urogenital schistosomiasis and susceptibility to bacterial UTI, the associated mechanisms are not understood. Hypothesized mechanisms include urinary stasis from fibrotic obstruction and host immunomodulation by the parasite. We published the first mouse model of S. haematobium-bacterial uropathogen co-infection (Hsieh et al., Infection and Immunity, 2014). In this model, a single bladder exposure to S. haematobium eggs triggers granuloma formation that can be seen by ultrasound and histology of bladder sections. This resembles human bladder schistosomiasis:

Adapted from Hsieh et al., Infection and Immunity, 2014

Co-exposure of the mouse bladder to S. haematobium eggs and bacterial uropathogens also triggered production, a cytokine classically associated with schistosomiasis:

Bladder cytokines were measured by Luminex assays after 2 days of UTI89 infection. Co-exposed (S. haematobium eggs and uropathogenic E. coli strain UTI89) mice are denoted by closed circles, mono-infected mice (UTI89 only) by open circles. (n=4/group). Adapted from Hsieh et al., Infection and Immunity, 2014

Importantly, we found that a single exposure to parasite eggs also makes BALB/c mice susceptible to bacterial UTI when they are otherwise resistant:

3000 S. haematobium eggs (Sh+UTI89; closed circles) or control vehicle (UTI89; open circles) were injected into the bladder walls of mice (A-C). 7 days later, all mice were transurethrally inoculated with 10E8 cfu UTI89. (A-B) Urine was collected for bacterial counts 1, 4, and 7 days post-UTI89 infection. Data shown were compiled from four independent experiments. (C) Urine bacterial titers in co-exposed mice were measured weekly (n=5). Bacterial cfu differences between groups were compared using Mann-Whitney U tests. *p<0.05, **, p<0.01, ***, p<0.001; horizontal bars (A-C) indicate median values. Adapted from Hsieh et al., Infection and Immunity, 2014

On occasion filamentous-appearing E. coli cells can be seen in the vicinity of eggs (ovoid objects below) within bladder granulomata:

Given the prominence of bladder IL-4 expression after exposure to S. haematobium eggs, we next asked whether this cytokine plays a role in susceptibility to bacterial UTI. Indeed, we found that ablation of IL-4 receptor alpha (IL-4Rα) signaling and neutralization of IL-4 restored the baseline resistance of BALB/c to bacterial UTI despite prior exposure to S. haematobium eggs:

Urine bacterial titers were determined in co-exposed wild type ("WT"), IL4Rα−/−, or 11B11 antibody-treated wild type mice 1 and 7 days post-UTI89 infection. Data were compiled from two to four independent experiments. Adapted from Hsieh et al., Infection and Immunity, 2014

In the course of characterizing the leukocytic infiltrate of bladders in our model, we found that numbers of NKT cells were decreased in co-exposed versus bacterial mono-infected bladders:

Flow cytometric analyses of single cell suspensions isolated from bacterial mono-infected and co-exposed bladders demonstrated the presence of NKT cells (DX5+CD3+). Co-exposed mice are denoted by "Sh+UTI89" (closed circles), mono-infected mice by "UTI89" (open circles). Adapted from Hsieh et al., Infection and Immunity, 2014

 Given that schistosome-induced, non-NKT cell leukocyte infiltration may dilute NKT cell numbers in the bladders of co-exposed mice without exerting a specific functional effect on these cells, we next examined NKT cell biology on a per-cell basis. Invariant NKT (iNKT) cells from co-exposed mice expressed less interferon-γ (IFN-γ) per cell compared to those from mice infected with UTI alone:

Intracellular cytokine staining of bladder iNKT cells from mono- and co-exposed mice (n=6/group). Data from two independent experiments are shown and separated by vertical dotted line. Adapted from Hsieh et al., Infection and Immunity, 2014

 Since NKT cell activation appeared to be compromised, we then examined the biology of CD1d, a crucial antigen-presenting molecule for NKT cells, and any associated links with IL-4. Accordingly, we found that co-exposure resulted in lower CD1d expression in bladder antigen-presenting cells (APC) than in bacterial UTI alone in an IL-4Rα-dependent fashion:

CD1d expression on CD11c+CD3-B220- DC cells and F4/80+CD11b+SiglecF- macrophages was analyzed in mono-infected ("WT UTI89", open circles), co-exposed ("WT Sh+UTI89", closed circles) wild type and co-exposed IL4Rα−/− ("IL4Rα−/− Sh+UTI89", open triangles) mice. Data are representative of one of two independent experiments. "MFI" denotes median fluorescence intensity. Treatment groups were compared using ANOVA followed by post hoc pairwise comparisons. *p<0.05, **, p<0.01, ***, p<0.001, ****, p<0.0005; horizontal bars indicate median values. Adapted from Hsieh et al., Infection and Immunity, 2014

Finally, co-exposed mice were protected from prolonged bacterial infection by administration of alpha-galactosylceramide, an iNKT cell agonist:

Effect of α-GalCer on UTI89 clearance in co-exposed mice. Co-exposed mice were given intraperitoneal α-GalCer (2 μg, "Sh+UTI89+α-GalCer") on Day 0, 2, and 5 (or no α-GalCer) after UTI89 infection. Urine bacterial titers were examined at 1 and 7 days post-UTI89 infection. Data were compiled from two to four independent experiments. *p<0.05, **, p<0.01, ***, p<0.001; horizontal bars indicate median values. "MFI" denotes median fluorescence intensity. Co-exposed mice are denoted by "Sh+UTI89" (closed circles). Student's t tests were used to compare values between treatment groups. Adapted from Hsieh et al., Infection and Immunity, 2014

Given that S. mansoni eggs produce copious amounts of the interleukin-4 inducing principle of S. mansoni eggs (IPSE), our theoretical model is that S. haematobium eggs, like their S. mansoni counterparts, induce basophil and/or T cell production of IL-4. We believe IL-4 acts upon bladder APC (macrophages and DC) to decrease their expression of CD1d and MHC Class II. In turn, this results in suboptimal bladder NKT cell activation for promoting clearance of bacterial urinary tract infection, a decreased IFN-γ:IL-4 ratio among bladder iNKT cells in particular, and prolonged bacteriuria:

These findings underscore the potential benefits of first clearing helminth infections prior to treating bacterial co-infections in affected individuals. In addition, our data indicate that, in some people with helminth infection and antibiotic-refractory or –resistant bacterial co-infections, NKT cell-directed therapies may be non-antibiotic-based alternatives.

We are also working with Sheryl Justice and Patrick Seed to better understand how bacterial uropathogens may avoid and subvert the host immune system through strategies such as formation of intracellular bacterial communities. Finally, we are collaborating with Lynette Cegelski's group to study the biofilm biology of UTI.

If you are a student, resident, or post-doctoral fellow interested in participating in this research as a member of the Hsieh laboratory, please visit our Opportunities page.


Footer Links: