Evidence of interspecies O antigen gene cluster transfer between Shigella boydii 15 and Escherichia fergusonii

Oral immunization of Escherichia albertii strain DM104 induces protective immunity against Shigella dysenteriae type 4 in mouse model

The recent rise of antibiotic resistance and lack of an effective vaccine make the scenario of shigellosis alarming in developing countries like Bangladesh. In recent years, our group reported the vaccine efficacy of a non-pathogenic Escherichia albertii strain DM104 in different animal models, where an ocularly administered vaccine in the guinea pig eye model against Shigella dysenteriae type 4 challenge showed high protective efficacy and also induced a high titer of serum IgG against S. dysenteriae type 4 whole cell lysate (WCL) and LPS. In this study, we report further evaluation of the non-invasive and non-toxic environmental strain DM104 as a vaccine candidate against S. dysenteriae type 4 in mice model. Oral immunization of live DM104 bacterial strain demonstrated better protective immunity in mice model by showing 90% protection in mice against live S. dysenteriae type 4 lethal dose challenge and by inducing effective humoral and mucosal immune responses.

Lipopolysaccharide modification in Gram-negative bacteria during chronic infection

The Gram-negative bacterial lipopolysaccharide (LPS) is a major component of the outer membrane that plays a key role in host-pathogen interactions with the innate immune system. During infection, bacteria are exposed to a host environment that is typically dominated by inflammatory cells and soluble factors, including antibiotics, which provide cues about regulation of gene expression. Bacterial adaptive changes including modulation of LPS synthesis and structure are a conserved theme in infections, irrespective of the type or bacteria or the site of infection. In general, these changes result in immune system evasion, persisting inflammation and increased antimicrobial resistance. Here, we review the modifications of LPS structure and biosynthetic pathways that occur upon adaptation of model opportunistic pathogens (Pseudomonas aeruginosa, Burkholderia cepacia complex bacteria, Helicobacter pylori and Salmonella enterica) to chronic infection in respiratory and gastrointestinal sites. We also discuss the molecular mechanisms of these variations and their role in the host-pathogen interaction.

The genomic signatures of Shigella evolution, adaptation and geographical spread

Shigella spp. are some of the key pathogens responsible for the global burden of diarrhoeal disease. These facultative intracellular bacteria belong to the family Enterobacteriaceae, together with other intestinal pathogens, such as Escherichia coli and Salmonella spp. The genus Shigella comprises four different species, each consisting of several serogroups, all of which show phenotypic similarity, including invasive pathogenicity. DNA sequencing suggests that this similarity results from the convergent evolution of different Shigella spp. founders. Here, we review the evolutionary relationships between Shigella spp. and E . coli, and we highlight how the genomic plasticity of these bacteria and their acquisition of a distinctive virulence plasmid have enabled the development of such highly specialized pathogens. Furthermore, we discuss the insights that genotyping and whole-genome sequencing have provided into the phylogenetics and intercontinental spread of Shigella spp.

An environmental Escherichia albertii strain, DM104, induces protective immunity to Shigella dysenteriae in guinea pig eye model

The environmental Escherichia albertii strain DM104, which cross-reacts serologically with Shigella dysenteriae was assessed for pathogenic properties, immunogenicity, and protective efficacy in different animal models to evaluate it as a vaccine candidate against S. dysenteriae, which causes the severe disease, shigellosis. The DM104 isolate was found to be non-invasive and did not produce any entero- or cyto-toxins. The strain also showed negative results in the mouse lethal activity assay. The non-pathogenic DM104 strain gave, however, a high protective efficacy as an ocularly administered vaccine in the guinea pig eye model against S. dysenteriae type 4 challenge. It also induced a high titer of serum IgG against S. dysenteriae type 4 whole cell lysate and lipopolysaccharide. Taken together, all these results indicate a good potential for the use of the DM104 as a live vaccine candidate against shigellosis.

Duplex PCR methods for the molecular detection of Escherichia fergusonii isolates from broiler chickens

Escherichia fergusonii is an emerging pathogen that has been isolated from a wide range of infections in animals and humans. Primers targeting specific genes, including yliE (encoding a conserved hypothetical protein of the cellulose synthase and regulator of cellulose synthase island), EFER_1569 (encoding a hypothetical protein, putative transcriptional activator for multiple antibiotic resistance), and EFER_3126 (encoding a putative triphosphoribosyl-dephospho-coenzyme A [CoA]), were designed for the detection of E. fergusonii by conventional and real-time PCR methods. Primers were screened by in silico PCR against 489 bacterial genomic sequences and by both PCR methods on 55 reference and field strains. Both methods were specific and sensitive for E. fergusonii, showing amplification only for this bacterium. Conventional PCR required a minimum bacterial concentration of approximately 10(2) CFU/ml, while real-time PCR required a minimum of 0.3 pg of DNA for consistent detection. Standard curves showed an efficiency of 98.5%, with an R(2) value of 0.99 for the real-time PCR assay. Cecal and cloacal contents from 580 chickens were sampled from broiler farms located in the Fraser Valley (British Columbia, Canada). Presumptive E. fergusonii isolates were recovered by enrichment and plating on differential and selective media. Of 301 total presumptive isolates, 140 (46.5%) were identified as E. fergusonii by biochemical profiling with the API 20E system and 268 (89.0%) using PCR methods. E. fergusonii detection directly from cecal and cloacal samples without preenrichment was achieved with both PCR methods. Hence, the PCR methods developed in this work significantly improve the detection of E. fergusonii.

Serological cross-reaction between O-antigens of Shigella dysenteriae type 4 and an environmental Escherichia albertii isolate

An environmental freshwater bacterial isolate, DM104, appearing as Shigella-like colonies on selective agar plates was found to show strong and specific serological cross-reactivity with Shigella dysenteriae type 4. Biochemical identification according to the analytical profile index, molecular serotyping by restriction of the amplified O-antigen gene cluster (rfb-RFLP), together with phylogenetic analysis of the 16S rRNA gene and multi-locus sequence analysis, identified the isolate as Escherichia albertii. rfb-RFLP of DM104, revealed a profile different from that of S. dysenteriae type 4. However, western blot analysis of extracted lipopolysaccharides demonstrated strong cross-reactivity with S. dysenteriae type 4 using specific monovalent antisera and a lipopolysaccharide gel banding profile similar to that of S. dysenteriae type 4. The observed O-antigen cross-reaction between an E. albertii isolate and S. dysenteriae extends our knowledge of the extent of O-antigen cross-reaction within the Escherichia/Shigella group of organisms, and offers the possibility of using DM104 and similar cross-reacting strains as shigellosis vaccine candidates.