Toxin ProducingEscherichia coliStrains Research Articles

Acquisition of plasmids from Shiga toxin-producingEscherichia colistrains had low or neutral fitness cost on commensalE. coli.

Although it has been hypothesized that the acquisition of plasmids-especially those bearing virulence factors and antimicrobial resistance genes-increases the energetic burden and reduces the fitness of a bacterium in general, some results have challenged this view, showing little or no effect on fitness after plasmid acquisition, which may lead to change in the view that there are evolutionary barriers for a wide spread of such plasmids among bacteria. Here, to evaluate the fitness impact of plasmid-encoded antibiotic resistance and virulence genes, plasmids from O26:H11, O111:H8, and O118:H16 Shiga toxin-producing Escherichia coli (STEC) human and bovine isolates were transferred to the non-virulent E. coli HS and K-12 MG1655 strains. Sequencing and PCR were used to characterize plasmids, and to identify the presence of antimicrobial resistance and/or virulence genes. The fitness impact of plasmids encoding virulence and antimicrobial resistance upon bacterial hosts was determined by pairwise growth competition. Plasmid profile analysis showed that STEC strains carried one or more high and low molecular weight plasmids belonging to the B/O, F, I, K, P, Q, and/or X incompatibility groups encoding virulence genes (SPATE-encodinggenes) and/or antimicrobial resistance genes (aadA1, strAB, tetA, and/or tetB). Competition experiments demonstrated that the biological cost of carriage of these plasmids by the commensal E. coli strain HS or the laboratory strain E. coli K-12 MG1655 was low or non-existent, ranging from - 4.7 to 5.2% per generation. This suggests that there are few biological barriers-or, alternatively, it suggests that there are biological barriers that we were not able to measure in this competition model-against the spread of plasmid encoding virulence and resistance genes from STEC to other, less pathogenic E. coli strains. Thus, our results, in opposition to a common view, suggest that the acquisition of plasmids does not significantly affect the bacteria fitness and, therefore, the theorized plasmid burden would not be a significant barrier for plasmid spread.

Hybrid genome assemblies of four Shiga toxin-producing Escherichia coli strains containing a complete locus of enterocyte effacement and an O-Island 122.

This study describes the hybrid genome assemblies of four Shiga toxin-producing Escherichia coli strains isolated from the recto-anal junction of slaughter-age Irish sheep. In silico serotyping and genome analysis determined that each of the strains harbored a Shiga-toxin subtype, a complete locus of enterocyte effacement, and a rare O-island 122.

Whole-Genome Sequencing Applied to the Molecular Epidemiology of Shiga Toxin-Producing Escherichia coli O157:H7 in Argentina.

Shiga toxin-producing Escherichia coli strains are worldwide associated with sporadic human infections and outbreaks. In this work, we report the availability of high-quality draft whole-genome sequences for 19 O157:H7 strains isolated in Argentina.

Adhesin-Encoding Genes from Shiga Toxin-Producing Escherichia coli Are More Prevalent in Atypical than in Typical Enteropathogenic E. coli

Four of six adhesin-encoding genes (lpfA, paa, iha, and toxB) from Shiga toxin-producing Escherichia coli strains were detected in typical and atypical enteropathogenic E. coli (EPEC) strains of various serotypes. Although the most prevalent gene was lpfA in both groups, paa was the only potential diarrhea-associated gene in atypical EPEC.

Protective Immunization of Mice with an Active-Site Mutant of Subtilase Cytotoxin of Shiga Toxin-Producing Escherichia coli

We have recently described a novel AB(5) cytotoxin produced by certain Shiga toxin-producing Escherichia coli strains. The A subunit of this toxin is a subtilase-like serine protease, while the B pentamer mediates binding to host cell glycolipid receptors. The subtilase cytotoxin is lethal for mice, causing extensive microvascular thrombosis as well as necrosis in the brain, kidneys, and liver. In the present study, we have immunized mice with a purified derivative of the toxin with a Ser272 --> Ala mutation in the A subunit which abolishes cytotoxicity. This elicited strong antibody responses, as judged by enzyme-linked immunosorbent assay, which conferred protection against intraperitoneal challenge with purified toxin. Immunized mice were also protected from weight loss resulting from oral challenge with an E. coli K-12 clone expressing the active toxin.

Structural analysis of phage-borne stx genes and their flanking sequences in shiga toxin-producing Escherichia coli and Shigella dysenteriae type 1 strains.

The stx-flanking regions of 49 Shiga toxin-producing Escherichia coli strains and nine Shigella dysenteriae serotype 1 strains containing either stx, stx(1), stx(2), or stx(2) variant genes, were examined. We analyzed these regions by PCR using a set of primers with one primer specific for the respective stx gene and a second primer complementary to sequences of Stx phages H-19B and 933W. We further characterized the amplification products by restriction endonuclease digestion and nucleotide sequencing. PCR products of stx(1)-containing E. coli strains of serogroups O157, O26, and 0103 showed the same lengths and similar restriction patterns. However, we failed to amplify the 3' stx-flanking region in stx(1)-harboring E. coli O111:H(-) strains. Stx2-producing E. coli strains revealed amplification products of different lengths and restriction patterns, suggesting greater heterogeneity than in stx(1)-positive strains. We also obtained specific PCR products for two Stx2c-producing and seven Stx2f-producing E. coli strains when they were subjected to PCR analysis. In nine S. dysenteriae type 1 strains, H-19B- and 933W-specific primers amplified only the 3' stx-flanking region. The results of our study demonstrate that the stx genes of all strains investigated are continuous with phage sequences. Whereas almost all strains except E. coli O111:H(-) strains were associated with a S-like gene, association with Q could not be demonstrated in nine S. dysenteriae type 1 strains and three E. coli strains. Furthermore, we showed that the organization of the stx-flanking regions is similar in all strains investigated, whereas fine-structure analysis showed subtle differences among the sequences examined. Our results support the hypothesis that stx genes in E. coli and S. dysenteriae are generally phage-borne.

Immunization of mice with live oral vaccine based on aSalmonella enterica(sv Typhimurium)aroAstrain expressing theEscherichia coliO111 O antigen

Shiga toxin-producingEscherichia colistrains of serogroup O111 are the most frequently isolated non-O157 strains causing outbreaks of gastroenteritis with haemolytic uraemic syndrome (HUS). O antigen is a major antigen in Gram-negative bacteria, and it has been shown that O111 is a protective antigen. AttenuatedSalmonella entericasv TyphimuriumaroAstrain STM-1 was used as a live carrier to express theE. coliO111 O antigen. Mice immunized intraperitoneally produced serum immunoglobulin G, and mice immunized orally produced serum immunoglobulin G and secretory immunoglobulin A in the intestine againstE. coliO111 cells as determined by enzyme-linked immunosorbent assays.