Phenotypic Heterogeneity in Expression of the K1 Polysaccharide Capsule of Uropathogenic Escherichia coli and Downregulation of the Capsule Genes during Growth in Urine

Abstract

Uropathogenic Escherichia coli (UPEC) is the major causative agent of uncomplicated urinary tract infections (UTI). The K1 capsule on the surface of UPEC strains is a key virulence factor, and its expression may be important in the onset and progression of UTI. In order to understand capsule expression in more detail, we analyzed its expression in the UPEC strain UTI89 during growth in rich medium (LB medium) and urine and during infection of a bladder epithelial cell line. Comparison of capsule gene transcription using a chromosomal gfp reporter fusion showed a significant reduction in transcription during growth in urine compared to that during growth in LB medium. When examined at the single-cell level, following growth in both media, capsule gene expression appears to be heterogeneous, with two distinct green fluorescent protein (GFP)-expressing populations. Using anti-K1 antibody, we showed that this heterogeneity in gene expression results in two populations of encapsulated and unencapsulated cells. We demonstrated that the capsule hinders attachment to and invasion of epithelial cells and that the unencapsulated cells within the population preferentially adhere to and invade bladder epithelial cells. We found that once internalized, UTI89 starts to produce capsule to aid in its intracellular survival and spread. We propose that this observed phenotypic diversity in capsule expression is a fitness strategy used by the bacterium to deal with the constantly changing environment of the urinary tract.

The Basics of Bacteriuria: Strategies of Microbes for Persistence in Urine

“…Nitrite in mildly acidified urine inhibits the growth of some uropathogens (Carlsson et al, 2001 ), and other abundant proteins such as Tamm-Horsfall glycoprotein are antimicrobial (Raffi et al, 2005 ; Säemann et al, 2005 ). Recently, the antimicrobial properties of urine were shown to include specific inhibition of both expression and function of UPEC type 1 pili (Greene et al, 2015 ), and downregulation of capsule genes (King et al, 2015 ). Individualistic urinary chemical features can also affect the antimicrobial properties of some antimicrobial urinary proteins such as siderocalin (Shields-Cutler et al, 2015 ).…”

AutA and AutR, Two Novel Global Transcriptional Regulators, Facilitate Avian Pathogenic Escherichia coli Infection

“…King et al . showed the phenotypic heterogeneity in the expression of K1 capsule during UPEC strain UTI89 adaptive response, when UTI89 withstands changeable environment of the urinary tract and undertakes intracellular survival 17 . King et al .…”

“…King et al . proposed that there might be unidentified regulators that can alter expression of K1 capsule under host-induced stimuli in vivo 17 . In this study, we confirmed that typical APEC strain DE205B also changed K1 capsule expression under different infection conditions.…”

“…K1 capsule of APEC/ExPEC is involved in survival and replication within non-phagocytosis cells, intracellular macrophage survival for disrupting host (phagocytosis) response modulation, and serum resistance to complement-mediated killing 12 13 14 15 . Interestingly, K1 capsule mutants of APEC/ExPEC appear to have higher adhesion rates during adherence on non-phagocytosis cells, but have lower intracellular survival within host cells, implying that presence of polysaccharide capsule might shield the virulence roles of short bacterial adhesins 15 16 17 .…”

Siderophore biosynthesis coordinately modulated the virulence-associated interactive metabolome of uropathogenic Escherichia coli and human urine

“…Moreover, the composition of human urine has a noticeable influence on the virulence of UPEC 10 11 . Generally, chemical exchange primarily accounts for metabolic interaction of UPEC and human urine and can be characterized as the “interactive metabolome”, which includes the utilized metabolome (metabolic cost) and excreted metabolome (metabolic donation) triggered by the interaction between UPEC and cultured human urine, by which the strains are capable of maintaining pathogenic growth in women’s bladders as the fundamental driver for causing infection 45 46 47 48 49 . In this study, we employed a combination of metabolomics and genetics 4 5 6 to discover and characterize the individualized interactive metabolome between UPEC and human urine that should be significantly differentiated from that between non-UPEC and human urine when the defined strains are cultured in pooled human urine.…”