In a previous study, induction of the serotype O157:H7 SOS response decreased expression in the clinical isolate PA20 at 30°C but strongly induced genes in the horizontally transferred-DNA regions (HTR), including many known virulence regulators. To determine the role of HTR regulators in the control of and curli, specific regulators were plasmid-expressed in the wild-type and mutant strains of PA20 and its biofilm-forming derivative, 20R2R. At 30°C, plasmid over-expression of the O157:H7 group 3 homolog, , strongly repressed PA20 transcription (>7-fold) while the group 1 homologs, and , resulted in smaller reductions (<2.
View Article and Find Full Text PDFThe high frequency of prophage insertions in the mlrA gene of clinical serotype O157:H7 isolates renders such strains deficient in csgD-dependent biofilm formation but prophage induction may restore certain mlrA properties. In this study we used transcriptomics to study the effect of high and low sulfamethoxazole-trimethoprim (SMX-TM) concentrations on prophage induction, biofilm regulation, and virulence gene expression in strain PA20 under environmental conditions following 5-hour and 12-hour exposures in broth or on agar. SMX-TM at a sub-lethal concentration induced strong RecA expression resulting in concentration- and time-dependent major transcriptional shifts with emphasis on up-regulation of genes within horizontally-transferred chromosomal regions (HTR).
View Article and Find Full Text PDFserotype O157:H7 strain B6914-MS1 is an isolate from the Centers for Disease Control and Prevention that is missing both Shiga toxin genes and has been used extensively in applied research studies. Here we report the genome sequence of strain B6914-ARS, a B6914-MS1 clone that has unique biofilm properties.
View Article and Find Full Text PDFExpression of the major biofilm components of E. coli, curli fimbriae and cellulose, requires the CsgD transcription factor. A complex regulatory network allows environmental control of csgD transcription and biofilm formation.
View Article and Find Full Text PDFEscherichia coli serotype O157:H7 strain PA20 is a Pennsylvania Department of Health clinical isolate. It has been used to study biofilm formation in O157:H7 clinical isolates, where the high incidence of prophage insertions in the mlrA transcription factor disrupts traditional csgD biofilm regulation. Here, we report the complete PA20 genome sequence.
View Article and Find Full Text PDFThe genome sequence of Escherichia coli serotype O157:H7 EDL933, a ground beef isolate from a 1983 hemorrhagic colitis outbreak, is a standard reference for comparative genomic studies of Shiga toxin-producing E. coli strains. Here, we report the genome sequence of a patient stool isolate from that outbreak, strain EDL932.
View Article and Find Full Text PDFProphage insertions in Escherichia coli O157:H7 mlrA contribute to the low expression of curli fimbriae and biofilm observed in many clinical isolates. Varying levels of CsgD-dependent curli/biofilm expression are restored to strains bearing prophage insertions in mlrA by mutation of regulatory genes affecting csgD Our previous study identified strong biofilm- and curli-producing variants in O157:H7 cultures that had lost the mlrA-imbedded prophage characteristic of the parent population, suggesting prophage excision as a mechanism for restoring biofilm properties. In this study, we compared genomic, transcriptomic and phenotypic properties of parent strain PA20 (stx1, stx2) and its prophage-cured variant, 20R2R (stx2), and confirmed the mechanism underlying the differences in biofilm formation.
View Article and Find Full Text PDFHigh variability in the expression of csgD-dependent, biofilm-forming and adhesive properties is common among Shiga toxin-producing Escherichia coli. Although many strains of serotype O157:H7 form little biofilm, conversion to stronger biofilm phenotypes has been observed. In this study, we screened different strains of serotype O157:H7 for the emergence of strong Congo-red (CR) affinity/biofilm-forming properties and investigated the underlying genetic mechanisms.
View Article and Find Full Text PDFBiofilm formation in most Escherichia coli strains is dependent on curli fimbriae and cellulose, and the production of both varies widely among pathogenic strains. Curli and cellulose production by colonies growing on agar are often identified by their affinity for Congo red dye (CR). However, media composition and incubation temperature can affect dye affinity and impose limitations on red phenotype detection by this method.
View Article and Find Full Text PDFThe biofilm life style helps bacteria resist oxidative stress, desiccation, antibiotic treatment, and starvation. Biofilm formation involves a complex regulatory gene network controlled by various environmental signals. It was previously shown that prophage insertions in mlrA and heterogeneous mutations in rpoS constituted major obstacles limiting biofilm formation and the expression of extracellular curli fibers in strains of Escherichia coli serotype O157:H7.
View Article and Find Full Text PDFBiofilm formation in Escherichia coli is a tightly controlled process requiring the expression of adhesive curli fibres and certain polysaccharides such as cellulose. The transcriptional regulator CsgD is central to biofilm formation, controlling the expression of the curli structural and export proteins and the diguanylate cyclase adrA, which indirectly activates cellulose production. CsgD itself is highly regulated by two sigma factors (RpoS and RpoD), multiple DNA-binding proteins, small regulatory RNAs and several GGDEF/EAL proteins acting through c-di-GMP.
View Article and Find Full Text PDFIn many Escherichia coli serotype O157 : H7 strains, defences against peroxide damage include the peroxiredoxin AhpCF and three catalases: KatG (catalase/peroxidase), KatE (catalase) and the plasmid-encoded KatP (catalase/peroxidase). AhpC and KatG basal expression is maintained by RpoS, and AhpC, KatG and KatP are all induced by OxyR/σ(70) in exponential phase. KatE is regulated by RpoS during stationary growth and is independent of OxyR.
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