The pig as translational model of urinary tract infection: recapitulating important aspects of human disease

Urinary tract infection (UTI), in particular cystitis, is a widespread disease in Denmark and the whole world and occurs in all age groups [1]. UTIs constitutes the most common nosocomial infection, the most common cause of sepsis and accounts for approximately 3000 deaths every year in Denmark alone [3, 133]. Community-acquired UTIs are characterized by a high frequency of recurrence, even in otherwise healthy women with no apparent risk factors [1].


A part from epidemiological data, much of what we know about the pathogenesis of UTI comes from experimental studies in cell-culture based assays and murine models of cystitis. In these models, uropathogenic Escherichia coli (UPEC), the most common etiological agent of UTI, has been shown to invade bladder epithelial cells forming intracellular dormant reservoir [134]. In mice, these reservoirs can survive antibiotic treatment and seed re-infections [121]. The intracellular pathogenic cascade has been suggested as a plausible explanation to recurrent UTIs in humans as well. However, despite being extensively demonstrated in mice through the last 20 years, only very few studies has indicated a similar pathogenesis in humans and the hypothesis have struggled to become accepted in clinical societies [134-137]. This may in part be explained by an increasing skepticism towards the translatability of murine models to human disease [4].


To bridge the gap between mice and humans, this Ph.D project aimed to investigate UPEC pathogenesis, including the intracellular pathogenic cascade, in a new large animal model of UTI in pigs. Pigs have been highlighted as excellent models of infectious diseases and share more similarities to humans in terms of genetics, immune physiology and urinary tract anatomy compared to their rodent counterpart [7].


Female domestic pigs (Landrace x Yorkshire, mix) of roughly 40 kg were used here. The pigs were inoculated through a urinary catheter with UPEC to induce cystitis. Pigs were inoculated with varying concentrations of bacteria to determine minimal infectious inoculum, i.e. the susceptibility to infection. Furthermore, by using a mutant lacking the T1F, one of the most well-described virulence factors of UPEC, the influence of this
fimbriae on infectious outcome was assessed in the porcine model. To investigate the intracellular pathogenic cascade, whole-bladders from infected pigs were investigated for the presence of intracellular bacteria following ex vivo and in vivo antibiotic treatment by analyzing splayed bladders with confocal laser scanning microscopy and plating homogenized tissue samples. Lastly, the model was adapted to facilitate studies of catheter-associated UTI (CAUTI), and with this, an efficacy study of a novel antimicrobial catheter was performed.


The results are consolidated in 5 manuscripts (3 published papers, 2 in peer-review) and show that pigs are highly susceptible to UTI, with only a few single bacteria of UPEC capable of successfully infecting this animal. This infectious potential is largely dependent on T1F, as the T1F-deficient mutant was strongly attenuated. Surprisingly, we found no evidence of intracellular persistence upon antibiotic treatment. In the CAUTI
model, we demonstrate proof-of-concept of an antimicrobial bladder catheter that effectively prevented CAUTI in all pigs.


In conclusion, the pig represents a robust model that recapitulates important aspects of human UTI. Thereby, the model is appropriate for studies of UTI pathogenesis as well as pre-clinical efficacy studies of new therapeutic treatments or interventions against UTI. Furthermore, the results of these studies show important differences in UTI pathogenesis between mice and pigs, particular in relation to intracellular persistence and thereby support that results from experiments in mice should be interpreted with caution.