20 research outputs found

    Genetic Dissection of an Exogenously Induced Biofilm in Laboratory and Clinical Isolates of E. coli

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    Microbial biofilms are a dominant feature of many human infections. However, developing effective strategies for controlling biofilms requires an understanding of the underlying biology well beyond what currently exists. Using a novel strategy, we have induced formation of a robust biofilm in Escherichia coli by utilizing an exogenous source of poly-N-acetylglucosamine (PNAG) polymer, a major virulence factor of many pathogens. Through microarray profiling of competitive selections, carried out in both transposon insertion and over-expression libraries, we have revealed the genetic basis of PNAG-based biofilm formation. Our observations reveal the dominance of electrostatic interactions between PNAG and surface structures such as lipopolysaccharides. We show that regulatory modulation of these surface structures has significant impact on biofilm formation behavior of the cell. Furthermore, the majority of clinical isolates which produced PNAG also showed the capacity to respond to the exogenously produced version of the polymer

    Complement-mediated lipopolysaccharide release and outer membrane damage in Escherichia coli J5: requirement for C9

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    Lipopolysaccharides (LPS) are major antigenic components of the outer membrane of Gram-negative bacteria and can stimulate activation of the complement system. Such activation leads to formation of the complement membrane attack complex (MAC) on the cell walls, LPS release and, in serum-sensitive strains, to cell death. In this study, Escherichia coli J5 strains, which incorporate exogenous galactose exclusively into LPS, were used to generate target strains with different LPS chemotypes, and the LPS of the strains was labelled with tritium ((3)H-LPS). The ability of normal human serum (NHS) and human complement-deficient sera to release LPS was subsequently monitored. NHS-induced release of 64–95Β·7% of (3)H-LPS within 30 min; overall, no significant difference was observed between release of LPS from E. coli J5 strains with different LPS chemotypes. In functional assays, maximum LPS release had occurred by 30 min and before maximum bacterial killing. Electron microscopy revealed NHS-induced outer-membrane disruption in the form of blebs at 15 min; at this time-point the inner membrane remained intact. Background LPS release and no bactericidal activity were detected in heat-inactivated serum or human sera deficient in C6, C7 or C8. The C9-deficient (C9D) serum had low bactericidal activity and failed to induce LPS release; however, addition of purified human C9 reconstituted its ability to release LPS. This study demonstrated the need for functional C9 molecules for LPS-releasing activities in serum-sensitive E. coli J5 strains
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