Context-Dependent Requirements for FimH and Other Canonical Virulence Factors in Gut Colonization by Extraintestinal Pathogenic Escherichia coli.

Extraintestinal pathogenic Escherichia coli (ExPEC) acts as a commensal within the mammalian gut but can induce pathology upon dissemination to other host environments such as the urinary tract and bloodstream. ExPEC genomes are likely shaped by evolutionary forces encountered within the gut, where the bacteria spend much of their time, provoking the question of how their extraintestinal virulence traits arose. The principle of coincidental evolution, in which a gene that evolved in one niche happens to be advantageous in another, has been used to argue that ExPEC virulence factors originated in response to selective pressures within the gut ecosystem. As a test of this hypothesis, the fitness of ExPEC mutants lacking canonical virulence factors was assessed within the intact murine gut in the absence of antibiotic treatment. We found that most of the tested factors, including cytotoxic necrotizing factor type 1 (CNF1), Usp, colibactin, flagella, and plasmid pUTI89, were dispensable for gut colonization. The deletion of genes encoding the adhesin PapG or the toxin HlyA had transient effects but did not interfere with longer-term persistence. In contrast, a mutant missing the type 1 pilus-associated adhesin FimH displayed somewhat reduced persistence within the gut. However, this phenotype varied dependent on the presence of specific competing strains and was partially attributable to aberrant flagellin expression in the absence of fimH These data indicate that FimH and other key ExPEC-associated factors are not strictly required for gut colonization, suggesting that the development of extraintestinal virulence traits is not driven solely by selective pressures within the gut.

Cell Printing in Complex Hydrogel Scaffolds.

Advancements in the microfabrication of soft materials have enabled the creation of increasingly sophisticated functional synthetic tissue structures for a myriad of tissue engineering applications. A challenge facing the field is mimicking the complex microarchitecture necessary to recapitulate proper morphology and function of many endogenous tissue constructs. This paper describes the creation of PEGDA hydrogel microenvironments (microgels) that maintain a high level of viability at single cell patterning scales and can be integrated into composite scaffolds with tunable modulus. PEGDA was stereolithographically patterned using a digital micromirror device to print single cell microgels at progressively decreasing length scales. The effect of feature size on cell viability was assessed and inert gas purging was introduced to preserve viability. A composite PEGDA scaffold created by this technique was mechanically tested and found to enable dynamic adjustability of the modulus. Together this approach advances the ability to microfabricate tissues that better mimic native constructs on cellular and subcellular length scales.