Assessment of Virulence of Uropathogenic Escherichia coli Type 1 Fimbrial Mutants in Which the Invertible Element Is Phase-Locked On or Off

Abstract

Type 1 fimbria is a proven virulence factor of uropathogenic Escherichia coli (UPEC), causing urinary tract infections. Expression of the fimbria is regulated at the transcriptional level by a promoter situated on an invertible element, which can exist in one of two different orientations. The orientation of the invertible element that allows the expression of type 1 fimbriae is defined as "on," and the opposite orientation, in which no transcription occurs, is defined as "off." During the course of a urinary tract infection, we have observed that the infecting E. coli population alternates between fimbriated and nonfimbriated states, with the fimbriated on orientation peaking at 24 h. We propose that the ability of the invertible element to switch orientations during infection is itself a virulence trait. To test this hypothesis, nucleotide sequence changes were introduced in the left inverted repeat of the invertible element of UPEC pyelonephritis strain CFT073 that locked the invertible elements permanently in either the on or the off orientation. The virulence of these mutants was assessed in the CBA mouse model of ascending urinary tract infection at 4, 24, 48, and 72 h postinoculation (hpi). We conducted independent challenges, in which bladders of mice were inoculated with either a single mutant or the wild type, and cochallenges, in which a mutant and the wild type were inoculated together to allow direct competition in the urinary tract. In both sets of experimental infections, the locked-off mutant was recovered from the urine, bladder, and kidneys in significantly lower numbers than the wild type at 24 hpi (P < 0.05), demonstrating its attenuation. Conversely, the locked-on mutant was recovered in higher numbers than the wild type at 24 hpi (P < 0.05), showing enhanced virulence of this mutant. No significant differences were seen between the mutants and wild type in the urine or the bladder at 48 or 72 hpi. However, the wild type outcompeted the locked-off mutant in the kidneys during the cochallenge experiment at 72 hpi (P ‫؍‬ 0.009). Overall, these data suggest that the ability of the invertible element controlling type 1 fimbria expression to phase vary contributes significantly to virulence early (24 hpi) in the course of a urinary tract infection by UPEC and most profoundly influences colonization of the bladder.

Expression of flagella is coincident with uropathogenic Escherichia coli ascension to the upper urinary tract

“…Using this technology, fliC expression was easily detectable over background luminescence produced by the promoterless P neg -lux construct. The early decrease observed for fliC expression in the bladder and subsequent peak of fliC expression in the kidneys is intriguing, because it is coincident with the time that UPEC strain CFT073 is known to reach and colonize the kidneys (6,26). Although it has been speculated that flagellum-mediated motility contributes to the movement of infection within the host (1, 2), the data presented in this study provide direct evidence that flagella of UPEC strain CFT073 are expressed at both the time (4-6 hpi) and location (ureters) at which UPEC ascend from the bladder to the kidneys.…”

Integrated regulatory responses of fimB to N -acetylneuraminic (sialic) acid and GlcNAc in Escherichia coli K-12

“…On the other hand, constitutive expression of type 1 fimbriae in uropathogens can increase virulence (32). Temperatures Ͼ37°C, low levels of leucine, high osmolarity, Neu 5 Ac, and GlcNAc all inhibit FimBcatalyzed off-to-on phase variation (21,22,57).…”

“…Thus, particularly in sialidasenegative bacteria like E. coli, Neu 5 Ac could be a key signal within the host milieu (21,31). A mutant containing the invertible element locked in the on orientation is more pathogenic in a mouse model for cystitis, and thus phase variation of fim can affect the host-parasite relationship (32). Here, we investigate the regulatory factors and signals required for the inhibition of FimB recombination in response to sialic acid.…”

ibeA, a virulence factor of avian pathogenic Escherichia coli

“…Virulence determinants common to APEC and ExPEC have been identified. They include the aerobactin iron transport system, the K1 capsule and type 1 and P fimbriae (Bahrani-Mougeot et al, 2002;Dho-Moulin & Fairbrother, 1999;Gunther et al, 2002;Hoffman et al, 1999;Mobley et al, 1993;Pourbakhsh et al, 1997;Torres et al, 2001). Vandemaele and colleagues also found a high level of homology between papG sequences, the P pilus adhesin gene from APEC isolates and papG sequences from mammalian E. coli isolates, including human isolates (Vandemaele et al, 2003;Johnson et al, 1997).…”