Uropathogenic Escherichia coli can cause cystitis at extremely low inocula in a pig model

Abstract

Urinary tract infection (UTI) is one of the most common bacterial infections worldwide. Experimental models that accurately reflect the high susceptibility to UTI in humans have, however, been lacking. This situation has limited detailed research into the early bladder colonization by uropathogens and the early innate defence mechanisms elicited to prevent this. We recently presented a model of urinary tract infection in pigs, animals that are naturally susceptible to UTI and have greater similarity to the physiology and anatomy of the human urinary tract than traditional rodent UTI models. In the current study, we used the pig model to investigate the minimal infectious inoculum of uropathogenic Escherichia coli , the most common cause of urinary tract infection. We show that in this animal a few individual bacteria that come into contact with the urothelium can give rise to fulminant cystitis, indicating the high infectious potential of uropathogenic E. coli .

Clean-catching urine from pigs: A method for collecting quality specimens for urinalysis and microbiological culturing in a laboratory environment

“…23 As a result of the high incidence of UPEC-associated UTIs, UPEC is the predominant model species used in experimental UTI studies and, to our knowledge, the only uropathogen species used in porcine UTI studies. 9,10,21,24 Therefore, in studies of UPEC or other members of the Enterobacteriaceae family, using selective blue agar is an excellent approach to minimize contamination when clean-catching urine specimens. When urine specimens from clean-catch were plated on a universal medium, 5% blood agar, bacterial contaminants were frequently detected (98% of samples) and occasionally appeared in relatively high numbers (13% of samples at 10 3 CFU · ml –1 ), suggesting that universal growth media can be a challenge if working with Gram-positive uropathogenic model organisms, such as Enterococcus faecalis or Staphylococcus saprophyticus , that is, bacterial species that are not culturable on selective blue agar.…”

“…Therefore, the potential influence of the experimental inoculation on the course on infection is difficult to assess; however, in a previous study we showed that inoculation with a non-pathogenic Pseudomonas aeruginosa using the same protocol did not result in any detectable bacteria 24 h after inoculation, suggesting that the experimental infection procedure does not lead to bladder colonization. 9 Since the main objective of this study was to develop a protocol for clean-catching urine specimens and to evaluate the quality in terms of contamination, we find it justified to use control specimens from the same animals before they are subjected to experimental inoculation. This also reduces the number of animals needed.…”

“…4 Pigs, on the other hand, have been highlighted as excellent models of human UTI because pigs (i) are more similar to humans in terms of anatomy and physiology of the kidneys and urinary tract, 5,6 (ii) share considerably more immunological parameters with humans compared with mice 7 and (iii) are the natural host of human uropathogens and highly susceptible to UTI. 8,9 Last, the size of the porcine bladder, which reflects that of humans, facilitates reliable collection of urine samples to monitor urinary bacterial titres and, thus, the course of disease. However, until now, urine specimens have been collected by either bladder catheterization or sterile bladder aspiration, which are both procedures that require the need for anaesthesia.…”

“…However, until now, urine specimens have been collected by either bladder catheterization or sterile bladder aspiration, which are both procedures that require the need for anaesthesia. [9][10][11][12] Although well-established protocols for shortterm anaesthesia exist, they often involve various combinations of opioids, benzodiazepines and alpha-2-agonists, which are associated with adverse effects such as obstipation, nausea, extended recovery, drug interactions or unwanted alterations in the animal's physiology that can interfere with the outcome of the study. [13][14][15] Therefore, the need for anaesthesia is a major limitation as it is not only stressful for the animal and increases procedural costs, but also limits the frequency of which urine specimens can be collected as daily anaesthesia for many days in a row is undesirable due to the concern for the animal's welfare.…”

Urinary bladder catheterisation of female pigs: Influence of bladder content and Escherichia coli urinary tract infection on procedural outcome

“…13 The authors have carried out extensive work with a porcine model of experimental urinary tract infection (UTI), in which catheterisation has been a fundamental procedure. 2,3,[17][18][19] It has also been the methodological step associated with most uncertainty, as catheterisation in some animals occasionally would take considerable time (up to an hour), similar to reports from others. 14 Consequently, controlled inoculation or timely urine sampling would occasionally be delayed because the catheter was difficult to insert, thus contributing to potential bias.…”