Escherichia coli type-1 fimbriae are critical to overcome initial bottlenecks of infection upon low-dose inoculation in a porcine model of cystitis

Abstract

Most uropathogenic Escherichia coli (UPEC) express type-1 fimbriae (T1F), a key virulence factor for urinary tract infection (UTI) in mice. Evidence that conclusively associates this pilus with uropathogenesis in humans has, however, been difficult to obtain. We used an experimental porcine model of cystitis to assess the role of T1F in larger mammals more closely related to humans. Thirty-one pigs were infected with UPEC strain UTI89 or its T1F deficient mutant, UTI89ΔfimH, at inoculum titres of 102 to 108 colony forming units per millilitre. Urine and blood samples were collected and analysed 7 and 14 days post-inoculation, and whole bladders were removed at day 14 and analysed for uroepithelium-associated UPEC. All animals were consistently infected and reached high urine titres independent of inoculum titre. UTI89ΔfimH successfully colonized the bladders of 1/6 pigs compared to 6/6 for the wild-type strain. Intracellular UPEC were detectable in low numbers in whole bladder explants. In conclusion, low doses of UPEC are able to establish robust infections in pigs, similar to what is presumed in humans. T1F are critical for UPEC to surpass initial bottlenecks during infection but may be dispensable once infection is established. While supporting the conclusions from mice studies regarding a general importance of T1F in successfully infecting the host, the porcine UTI models’ natural high, more human-like, susceptibility to infection, allowed us to demonstrate a pivotal role of T1F in initial establishment of infection upon a realistic low-inoculum introduction of UPEC in the bladder.

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

“…Pigs are receiving increasing attention as biomedical models for vaccine research and pharmacological studies in many fields of human health, but have only recently been used in cystitis research [13]. This study, as well as previous work with the model, demonstrates the potential of using pigs as an appropriate UTI model [9]. In particular, the high susceptibility to infection is critical, as potential vaccine efficacy, host response functions or pathogen virulence factors may be masked by an exaggerated inoculum that outreaches that of a natural infection.…”

“…ml −1 . Three LY pigs were lightly sedated as previously described [9], and catheterized with a ch. 10 foley catheter (Rüsch) to empty the bladder, after which 100 ml of the inoculum was instilled into the bladder for a final inoculum of approximately 10 3 total bacteria [9].…”

“…Two breeds of female pigs were used, Landrace x Yorkshire (crossbreed) (LY) of 40 kg (n=5) and Göttingen Minipigs (GM) of 15 kg (n=2). The model in general has been described previously [5,7,9]. Bacterial inoculum was prepared by preincubating the reference UPEC cystitis strain UTI89 in lysogeny broth (LB) to induce type pili expression, similar to murine UTI models [10].…”

“…Three LY pigs were lightly sedated as previously described [9], and catheterized with a ch. 10 foley catheter (Rüsch) to empty the bladder, after which 100 ml of the inoculum was instilled into the bladder for a final inoculum of approximately 10 3 total bacteria [9]. After 5 min, care was taken to empty the bladder completely by repositioning the catheter multiple times with the animals in supine and side positions to remove the inoculum and minimize residual urine.…”

Escherichia marmotae—a Human Pathogen Easily Misidentified as Escherichia coli

“…Further, all Es. marmotae contained csgB/D/E/F/G , which are genes facilitating production of extracellular curli proteins involved in matrixes promoting cellular adhesion and biofilm formation ( 20 ) as well as fimA/B/C/D/E/F/G/H/I encoding type 1 fimbriae associated with urinary tract infection ( 21 ). They also harbor ompA , which encodes the outer membrane protein A associated with several pathogenic properties, including evasion of host defense systems during intracellular migration in neonatal meningitis and inactivation of the complement system ( 22 ).…”