Abstract
Pathogens are exposed to a multitude of harmful conditions imposed by the environment of the host. Bacterial responses against these stresses are pivotal for successful host colonization and pathogenesis. In the case of many E. coli strains, type 1 fimbriae (pili) are an important colonization factor that can contribute to diseases such as urinary tract infections and neonatal meningitis. Production of type 1 fimbriae in E. coli is dependent on an invertible promoter element, fimS, which serves as a phase variation switch determining whether or not a bacterial cell will produce type 1 fimbriae. In this review, we present aspects of signaling and stress involved in mediating regulation of type 1 fimbriae in extraintestinal E. coli; in particular, how certain regulatory mechanisms, some of which are linked to stress response, can influence production of fimbriae and influence bacterial colonization and infection. We suggest that regulation of type 1 fimbriae is potentially linked to environmental stress responses, providing a perspective for how environmental cues in the host and bacterial stress response during infection both play an important role in regulating extraintestinal pathogenic E. coli colonization and virulence.
Highlights
The survival of microorganisms is highly dependent on their ability to adapt to a frequently changing environment and to respond to a variety of environmental cues.When important environmental changes occur, bacteria need to rapidly respond and adjust through complex transcriptional or post-transcriptional regulatory mechanisms [1].Regarding bacterial pathogens, this adaptation is an important feature for survival and proliferation during colonization in different host anatomical niches that may represent distinct microenvironments
The specific contribution that this small RNA plays in the regulation of type 1 fimbriae is currently unknown (Table 2) but studies are in progress to determine the pathways and the mechanisms of how ryfA acts on fim switching [52]
E. coli strains have developed intricate regulatory pathways in order to acquire specificity in their adaptation to environmental conditions and that can affect control of type 1 fimbriae expression which is mediated by the orientation of an invertible ON/OFF promoter-containing switch
Summary
The survival of microorganisms is highly dependent on their ability to adapt to a frequently changing environment and to respond to a variety of environmental cues. The genomewide transcriptional response of ExPEC during colonization of the host has provided insight into genes and virulence factors that may contribute to adaptation, such as iron and heme import systems, toxins, adhesins, lipopolysaccharides, invasins, capsules, and antibiotic resistance genes. These genes are encoded on mobile genetic elements, such as bacteriophages, transposons, plasmids, or in specific regions called Pathogenicity Islands, which are frequently found in ExPEC [8,11]. One of the most important virulence factors of pathogenic E. coli is type 1 fimbriae This fimbrial adhesin can mediate bacterial attachment to and invasion of host cells and is subject to regulation through phase variation by a variety of environmental signals. The following sections will present the current state of knowledge for general and specific regulators of stress known in ExPEC and the impact of type 1 fimbriae regulation
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