Functional Insights From KpfR, a New Transcriptional Regulator of Fimbrial Expression That Is Crucial for Klebsiella pneumoniae Pathogenicity

Abstract

Although originally known as an opportunistic pathogen, Klebsiella pneumoniae has been considered a worldwide health threat nowadays due to the emergence of hypervirulent and antibiotic-resistant strains capable of causing severe infections not only on immunocompromised patients but also on healthy individuals. Fimbriae is an essential virulence factor for K. pneumoniae, especially in urinary tract infections (UTIs), because it allows the pathogen to adhere and invade urothelial cells and to form biofilms on biotic and abiotic surfaces. The importance of fimbriae for K. pneumoniae pathogenicity is highlighted by the large number of fimbrial gene clusters on the bacterium genome, which requires a coordinated and finely adjusted system to control the synthesis of these structures. In this work, we describe KpfR as a new transcriptional repressor of fimbrial expression in K. pneumoniae and discuss its role in the bacterium pathogenicity. K. pneumoniae with disrupted kpfR gene exhibited a hyperfimbriated phenotype with enhanced biofilm formation and greater adhesion to and replication within epithelial host cells. Nonetheless, the mutant strain was attenuated for colonization of the bladder in a murine model of urinary tract infection. These results indicate that KpfR is an important transcriptional repressor that, by negatively controlling the expression of fimbriae, prevents K. pneumoniae from having a hyperfimbriated phenotype and from being recognized and eliminated by the host immune system.

SdiA, a Quorum-Sensing Regulator, Suppresses Fimbriae Expression, Biofilm Formation, and Quorum-Sensing Signaling Molecules Production in Klebsiella pneumoniae

“…SdiA-deficient ATCC 10031 mutant strain was generated using TargeTron Gene Knockout System (Sigma-Aldrich), following a protocol previously standardized by us ( Gomes et al, 2021 ). The TargeTron system produces an RNA-protein complex (RNP) that inserts a modified group II intron of Lactococcus lactis (L1.…”

“…Biofilm formation assays were carried out conducted in 96-well microtiter plates as described previously ( Gomes et al, 2021 ). Saturated cultures of the bacterial strains were harvested by centrifugation and resuspended in LB broth to a final concentration of 10 6 cells/mL.…”

“…Yeast agglutination assays were performed to investigate the expression of type 1 fimbriae by the K. pneumoniae strains. The assays were conducted on Kline concavity slides as described previously, with minor modifications ( Gomes et al, 2021 ). Overnight cultures of the bacterial strains were inoculated (1:100) into fresh LB broth supplemented or not with C8-HSL and cultured until they reached O.D.…”

From Klebsiella pneumoniae Colonization to Dissemination: An Overview of Studies Implementing Murine Models

“…The balance regulation of fimbriae expression is therefore essential for bacterial in vivo colonization of the urinary site. A K. pneumoniae K2 mutant deficient for the KpfR transcriptional repressor of a type 1-like fimbriae that exhibited a hyperfimbriated phenotype colonized the mouse bladder less extensively than the wild-type strain 24 h post-infection and was more rapidly eliminated from the urinary tract [129]. The specific role of the K. pneumoniae type 3 surface adhesin (Mrk) has also been investigated in murine models of urinary tract infection.…”

Current Stage in the Development of Klebsiella pneumoniae Vaccines

“…The fimbriae components encoded by the mrk gene cluster are responsible for the type III fimbrial subunits, which are essential for adhesion and biofilm formation on biotic and abiotic surfaces [101,102]. Other fimbriae clusters have been identified [103], although some of these new clusters are part of the accessory genome, and their distribution is species-dependent [2].…”