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  • Blackwell Science Ltd  (4)
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  • 1
    ISSN: 1365-2958
    Source: Blackwell Publishing Journal Backfiles 1879-2005
    Topics: Biology , Medicine
    Notes: Enteroaggregative Escherichia coli (EAEC) forms thick biofilms on the intestinal mucosa. Here, we show that most EAEC strains form a biofilm on glass or plastic surfaces when grown in cell culture medium with high sugar and osmolarity. Biofilm-forming ability in two prototype EAEC strains required aggregative adherence fimbriae (AAF), although many other EAEC strains that do not express AAF also developed biofilms under these conditions. Ten thousand transposon mutants of EAEC strain 042 were isolated, and 100 were found to be deficient in biofilm formation. Of these, 93 were either deficient in in vitro growth or mapped to genes known to be required for AAF/II expression. Of the seven remaining insertions, five mapped to one of two unsuspected loci. Two insertions involved the E. coli chromosomal fis gene, a DNA-binding protein that is involved in growth phase-dependent regulation. Using reverse transcription–polymerase chain reaction (RT–PCR), we determined that the effect of fis was at the level of transcription of the AAF/II activator aggR. Biofilm formation also required the product of the yafK gene, which is predicted to encode a secreted 28 kDa protein. The yafK product is required for transcription of AAF/II-encoding genes. Our data do not suggest a role for type 1 fimbriae or motility in biofilm formation. EAEC appears to form a novel biofilm, which may be mediated solely by AAF and may reflect its interactions with the intestinal mucosa.
    Type of Medium: Electronic Resource
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  • 2
    ISSN: 1365-2958
    Source: Blackwell Publishing Journal Backfiles 1879-2005
    Topics: Biology , Medicine
    Notes: Urinary tract infection (UTI) is a very common extraintestinal infection, and Escherichia coli is by far the most common causative organism. Uropathogenic E. coli possess traits that distinguish them from commensal strains of E. coli, such as secretion systems that allow virulence factors to be targeted to extracytoplasmic compartments. One of at least five characterized secretion mechanisms is the autotransporter system, which involves translocation of a protein across the inner membrane, presumably via the sec system, and across the outer membrane through a β-barrel porin structure formed by the carboxy-terminus autotransporter domain. We identified a 107 kDa protein that was expressed significantly more often by E. coli strains associated with the clinical syndrome of acute pyelonephritis than by faecal strains (P = 0.029). We isolated the protein from E. coli CFT073, a strain cultured from the blood and urine of a patient with acute pyelonephritis. The N-terminal amino acid sequence showed highest similarity to two known SPATE (serine protease autotransporters of Enterobacteriaceae) proteins, Pet and EspC. Using a 509 bp probe from the 5′ region of pet, 10 cosmid clones of an E. coli CFT073 gene library were positive for hybridization. From one cosmid clone, a 7.5 kb EcoRI restriction fragment, which reacted strongly with the probe, was shown to include the entire 3885 bp gene. The predicted 142 kDa protein product possesses the three domains that are typical of SPATE autotransporters: an unusually long signal sequence of 49 amino acids; a 107 kDa passenger domain containing a consensus serine protease active site (GDSGSG); and a C-terminal autotransporter domain of 30 kDa. The protein exhibited serine protease activity and displayed cytopathic activity on VERO primary kidney, HK-2 bladder and HEp-2 cell lines; the name Sat (secreted autotransporter toxin) was derived from these properties. In addition, Sat antibodies were present in the serum of mice infected with E. coli CFT073. Based upon its association with pathogenic isolates, its cytopathic phenotype and its ability to elicit a strong antibody response after infection, we postulate that Sat represents a novel virulence determinant of uropathogenic E. coli.
    Type of Medium: Electronic Resource
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  • 3
    Electronic Resource
    Electronic Resource
    Oxford BSL : Blackwell Science Ltd
    Molecular microbiology 33 (1999), S. 0 
    ISSN: 1365-2958
    Source: Blackwell Publishing Journal Backfiles 1879-2005
    Topics: Biology , Medicine
    Notes: The expression of most bacterial genes is controlled at the level of transcription via promoter control mechanisms that permit a graded response. However, an increasing number of bacterial genes are found to exhibit an ‘all-or-none’ control mechanism that adapts the bacterium to more than one environment. One such mechanism is phase variation, traditionally defined as the high-frequency ON↔OFF switching of phenotype expression. Phase variation events are usually random, but may be modulated by environmental conditions. The mechanisms of phase variation events and their significance within the microbial community are discussed here.
    Type of Medium: Electronic Resource
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  • 4
    Electronic Resource
    Electronic Resource
    Oxford BSL : Blackwell Science Ltd
    Molecular microbiology 33 (1999), S. 0 
    ISSN: 1365-2958
    Source: Blackwell Publishing Journal Backfiles 1879-2005
    Topics: Biology , Medicine
    Type of Medium: Electronic Resource
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