Intestinal colonization by the foodborne pathogen Escherichia coli O157:H7 leads to serious disease symptoms, including hemolytic uremic syndrome (HUS) and hemorrhagic colitis (HC). Synthesis of one or more Shiga toxins (Stx) is essential for HUS and HC development. The genes encoding Stx, including Stx2a, are found within a lambdoid prophage integrated in the E. coli O157:H7 chromosome. Enhanced Stx2a expression was reported when specific non-pathogenic E. coli strains were co-cultured with E. coli O157:H7, and it was hypothesized that this phenotype required the non-pathogenic E. coli to be sensitive to stx-converting phage infection. We tested this hypothesis by generating phage resistant non-pathogenic E. coli strains where bamA (an essential gene and Stx phage receptor) was replaced with an ortholog from other species. Such heterologous gene replacement abolished the ability of the laboratory strain E. coli C600 to enhance toxin production when co-cultured with E. coli O157:H7 strain PA2, which belongs to the hypervirulent clade 8. The extracellular loops of BamA (loop 4, 6, 7) were further shown to be important for infection by stx2a-converting phages. However, similar gene replacement in another commensal E. coli, designated 1.1954, revealed a bamA-independent mechanism for toxin amplification. Toxin enhancement by 1.1954 was not the result of phage infection through an alternative receptor (LamB or FadL), lysogen formation by stx2a-converting phages, or the production of a secreted molecule. Collectively, these data suggest that non-pathogenic E. coli can enhance toxin production through at least two mechanisms.

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Escherichia 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.

Shigella species are a major cause of gastroenteritis worldwide, and Shigella sonnei is the most common species isolated within the United States. Previous surveillance work in Pennsylvania documented increased antimicrobial resistance (AMR) in S. sonnei associated with reported illnesses. The present study examined a subset of these isolates by whole genome sequencing (WGS) to determine the relationship between domestic and international isolates, to identify genes that may be useful for identifying specific Global Lineages of S. sonnei and to test the accuracy of WGS for predicting AMR phenotype. A collection of 22 antimicrobial-resistant isolates from patients infected within the United States or while travelling internationally between 2009 and 2014 was chosen for WGS. Phylogenetic analysis revealed both international and domestic isolates were one of two previously defined Global Lineages of S. sonnei , designated Lineage II and Lineage III. Twelve of 17 alleles tested distinguish these two lineages. Lastly, genome analysis was used to identify AMR determinants. Genotypic analysis was concordant with phenotypic resistance for six of eight antibiotic classes. For aminoglycosides and trimethoprim, resistance genes were identified in two and three phenotypically sensitive isolates, respectively. This article contains data hosted by Microreact .

word count: 315 15 Text word count: 5028 16 17 Abstract 24Escherichia coli O157:H7 is a foodborne pathogen, implicated in various multi-state 25 outbreaks. It encodes Shiga toxin on a prophage, and Shiga toxin production is linked to phage 26induction. An E. coli strain, designated 0.1229, was identified that amplified Stx2a production 27 when co-cultured with E. coli O157:H7 strain PA2. Growth of PA2 in 0.1229 cell-free 28 supernatants had a similar effect, even when supernatants were heated to 100°C for 10 min, but 29 not after treatment with Proteinase K. The secreted molecule was shown to use TolC for export 30 and the TonB system for import. The genes sufficient for production of this molecule were 31 localized to a 5.2 kb region of a 12.8 kb plasmid. This region was annotated, identifying 32 hypothetical proteins, a predicted ABC transporter, and a cupin superfamily protein. These genes 33were identified and shown to be functional in two other E. coli strains, and bioinformatic 34 analyses identified related gene clusters in similar and distinct bacterial species. These data 35 collectively suggest E. coli 0.1229 and other E. coli produce a microcin that induces the SOS 36 response in target bacteria. Besides adding to the limited number of microcins known to be 37 produced by E. coli, this study provides an additional mechanism by which stx2a expression is 38 increased in response to the gut microflora. 39 40