Response of Extraintestinal Pathogenic Escherichia coli to Human Serum Reveals a Protective Role for Rcs-Regulated Exopolysaccharide Colanic Acid

Miajlović, Helen; Cooke, Niamh M.; Moran, Gary P.; Rogers, Thomas R.; Smith, Stephen G.

doi:10.1128/iai.00800-13

Cited by 51 publications

(71 citation statements)

References 63 publications

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“…First, we determined the serum susceptibility of E. coli strain CFT073. Our results show that CFT073 is not strictly serum resistant as previously reported (6,8,9,31,32). Rather, only a fraction of cells survived serum treatment (Fig.…”

Section: Discussionsupporting

confidence: 71%

“…The CFT073 strain was isolated from the blood of a patient with acute pyelonephritis, so it is representative of UPEC strains that can cause bacteremia (25). CFT073 has been reported to be serum resistant (6,8,9,31,32). However, the experimental conditions for defining serum resistance are not standardized; the growth phase of the harvested bacteria, bacterial cell density, serum concentration, and incubation time can influence the number of cells that survive in the presence of serum (11)(12)(13)(14)33).…”

Section: Subpopulation Of Cft073 Cells Is Tolerant To Human Serummentioning

confidence: 99%

“…Pathogens often resist recognition and subsequent complement activation owing to their surface capsular polysaccharide, which masks underlying structures and by itself activates complement poorly (5)(6)(7). In addition, secretion of the exopolysaccharide colanic acid protects UPEC from complement-mediated killing (8). Modification of lipopolysaccharide (LPS) is also important for complement evasion (9,10).…”

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Phenotypic Heterogeneity Enables Uropathogenic Escherichia coli To Evade Killing by Antibiotics and Serum Complement

et al. 2015

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Uropathogenic strains of Escherichia coli (UPEC) are the major cause of bacteremic urinary tract infections. Survival in the bloodstream is associated with different mechanisms that help to resist serum complement-mediated killing. While the phenotypic heterogeneity of bacteria has been shown to influence antibiotic tolerance, the possibility that it makes cells refractory to killing by the immune system has not been experimentally tested. In the present study we sought to determine whether the heterogeneity of bacterial cultures is relevant to bacterial targeting by the serum complement system. We monitored cell divisions in the UPEC strain CFT073 with fluorescent reporter protein. T he immune system has several pathways for recognizing and killing pathogenic bacteria. However, some pathogenic bacteria can maintain infection in mammalian hosts despite inflammation, specific antimicrobial mechanisms, and a robust adaptive immune response and can therefore give rise to persistent infection (1). Uropathogenic Escherichia coli (UPEC) causes recurrent urinary tract infections that can progress from the lower to the upper urinary tract and can lead to the dissemination of bacteria into the bloodstream.The complement system is part of the defense against invading pathogens, with an essential role in both innate and adaptive immunity (2). It is composed of more than 40 plasma and membrane proteins. It can be activated via three distinct routes: the classical (antibody dependent), lectin, and alternative pathways. Activation of complement cascades leads to the formation of the key component C3b on the bacterial surface, which stimulates phagocytosis. Late complement components (C5 to C9 proteins) are also activated via C3b, resulting in the formation of the membrane attack complex (MAC) causing cell lysis (2). The primary source of complement is blood, but complement proteins are also synthesized by a variety of other cell types and tissues (3).Bacterial resistance to serum complement killing depends on the presence or absence of antigenic outer membrane proteins (4). Pathogens often resist recognition and subsequent complement activation owing to their surface capsular polysaccharide, which masks underlying structures and by itself activates complement poorly (5-7). In addition, secretion of the exopolysaccharide colanic acid protects UPEC from complement-mediated killing (8). Modification of lipopolysaccharide (LPS) is also important for complement evasion (9, 10). It has been shown that serum sensitivity depends on the bacterial growth phase; cells are more readily killed by serum during early logarithmic phase (11)(12)(13)(14). However, there are examples showing that exponential-phase cells are more resistant to complement-mediated killing than stationary-phase cells (15,16). That phenomenon is largely explained by the growth-phase-dependent expression of antigens, capsule, and LPS modification (14, 15). Cell size can also be an important determinant of complement-mediated killing, since larger or aggregated cells ...

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Section: Discussionsupporting

confidence: 71%

Section: Subpopulation Of Cft073 Cells Is Tolerant To Human Serummentioning

confidence: 99%

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Phenotypic Heterogeneity Enables Uropathogenic Escherichia coli To Evade Killing by Antibiotics and Serum Complement

et al. 2015

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“…The mutant was especially deficient in colonizing the heart tissue, the lung, and the spleen, leading the authors to infer that this was "direct evidence for an association of colanic acid with virulence and fitness" (46). CA also reportedly imparts serum resistance to extraintestinal pathogenic E. coli (ExPEC) (45,(47)(48)(49). For example, only 3% of an ExPEC ⌬wcaDE mutant and Ͻ20% of an rcsB mutant survived exposure to human serum (48), and a strain lacking any of three CA genes (wcaF, wcaH, or wcaI) was more sensitive to serum killing (47).…”

Section: Figmentioning

confidence: 99%

“…CA also reportedly imparts serum resistance to extraintestinal pathogenic E. coli (ExPEC) (45,(47)(48)(49). For example, only 3% of an ExPEC ⌬wcaDE mutant and Ͻ20% of an rcsB mutant survived exposure to human serum (48), and a strain lacking any of three CA genes (wcaF, wcaH, or wcaI) was more sensitive to serum killing (47). Finally, wcaD and wcaE mutants of enterohemorrhagic E. coli (EHEC) strain O157:H7 grow less well under acidic conditions, at high temperatures, or in simulated stomach acid, suggesting that CA protects EHEC against these conditions (50,51).…”

Section: Figmentioning

confidence: 99%

Colanic Acid Intermediates Prevent De Novo Shape Recovery of Escherichia coli Spheroplasts, Calling into Question Biological Roles Previously Attributed to Colanic Acid

Ranjit

Young

2016

J Bacteriol

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After losing their protective peptidoglycan, bacterial spheroplasts can resynthesize a cell wall to recreate their normal shape. In Escherichia coli, this process requires the Rcs response. In its absence, spheroplasts do not revert to rod shapes but instead form enlarged spheroids and lyse. Here, we investigated the reason for this Rcs requirement. Rcs-deficient spheroids exhibited breaks and bulges in their periplasmic spaces and failed to synthesize a complete peptidoglycan cell wall, indicating that the bacterial envelope was defective. To determine the Rcs-dependent gene(s) required for shape recovery, we tested spheroplasts lacking selected RcsB-regulated genes and found that colanic acid (CA) biosynthesis appeared to be involved. Surprisingly, though, extracellular CA was not required for recovery. Instead, lysis was caused by mutations that interrupted CA biosynthesis downstream of the initial glycosyl transferase, WcaJ. Deleting wcaJ prevented lysis of spheroplasts lacking ensuing steps in the pathway, and providing WcaJ in trans to a mutant lacking the entire CA operon triggered spheroplast enlargement and lysis. Thus, CA is not required for spheroplast recovery. Instead, CA intermediates accumulate as dead-end products which inhibit recovery of wallless cells. The results strongly imply that CA may not be required for the survival E. coli L-forms. More broadly, these findings mandate that previous conclusions about the role of colanic acid in biofilm formation or virulence must be reevaluated. IMPORTANCEWall-less bacteria can resynthesize their walls and recreate a normal shape, which in Escherichia coli requires the Rcs response. While attempting to identify the Rcs-dependent gene required for shape recovery, we found that colanic acid (CA) biosynthesis appeared to be involved. Surprisingly, though, cell death was caused by mutations that interrupted CA biosynthesis downstream of the initial step in the pathway, creating dead-end compounds that inhibited recovery of wall-less cells. When testing for the biological role of CA, most previous experiments used mutants that would accumulate these deadly intermediates, meaning that all prior conclusions must be reexamined to determine if the results were caused by these lethal side effects instead of accurately reflecting the biological purpose of CA itself. Bacterial cell shape is determined by coordinated and dynamic interactions among cytoskeletal elements, peptidoglycan synthesis, and cell division (as reviewed in references 1 and 2), and the wall and some of its morphological characteristics contribute to cell survival in suboptimal or hostile environments (3). For example, the host immune system elaborates several antibacterial factors, including lysozyme, cationic antimicrobial peptides, and protein complexes, which target the cell envelope and trigger bacterial lysis (4-6). In particular, lysozyme removes the peptidoglycan wall and leads to cell rupture. However, such cells may not lyse if they are immersed in an osmotically protective medi...

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Pathogenesis of Kingella kingae Disease

Porsch

Rempe

2016

Advances in Understanding Kingella Kingae

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Response of Extraintestinal Pathogenic Escherichia coli to Human Serum Reveals a Protective Role for Rcs-Regulated Exopolysaccharide Colanic Acid

Cited by 51 publications

References 63 publications

Phenotypic Heterogeneity Enables Uropathogenic Escherichia coli To Evade Killing by Antibiotics and Serum Complement

Phenotypic Heterogeneity Enables Uropathogenic Escherichia coli To Evade Killing by Antibiotics and Serum Complement

Colanic Acid Intermediates Prevent De Novo Shape Recovery of Escherichia coli Spheroplasts, Calling into Question Biological Roles Previously Attributed to Colanic Acid

Pathogenesis of Kingella kingae Disease

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