Isolation, characterization and comparative genomics of bacteriophage SfIV: a novel serotype converting phage from Shigella flexneri

BACKGROUND Shigella flexneri is the major cause of shigellosis in the developing countries. The O-antigen component of the lipopolysaccharide is one of the key virulence determinants required for the pathogenesis of S. flexneri. The glucosyltransferase and/or acetyltransferase genes responsible for the modification of the O-antigen are encoded by temperate serotype converting bacteriophage present in the S. flexneri genome. Several serotype converting phages have previously been isolated and characterized, however, attempts to isolate a serotype converting phage which encodes the modification genes of serotypes 4a strain have not been successful. RESULTS In this study, a novel temperate serotype converting bacteriophage SfIV was isolated. Lysogenisation of phage SfIV converted serotype Y strain to serotype 4a. Electron microscopy indicated that SfIV belongs to Myoviridae family. The 39,758 bp genome of phage SfIV encompasses 54 open reading frames (orfs). Protein level comparison of SfIV with other serotype converting phages of S. flexneri revealed that SfIV is similar to phage SfII and SfV. The comparative analysis also revealed that SfIV phage contained five proteins which were not found in any other phages of S. flexneri. These proteins were: a tail fiber assembly protein, two hypothetical proteins with no clear function, and two other unknown proteins which were encoded by orfs present on a moron, that presumably got introduced in SfIV genome from another species via a transposon. These unique proteins of SfIV may play a role in the pathogenesis of the host. CONCLUSIONS This study reports the isolation and complete genome sequence analysis of bacteriophage SfIV. The SfIV phage has a host range significantly different from the other phages of Shigella. Comparative genome analysis identified several proteins unique to SfIV, which may potentially be involved in the survival and pathogenesis of its host. These findings will further our understanding on the evolution of these phages, and will also facilitate studies on development of new phage vectors and therapeutic agents to control infections caused by S. flexneri

A novel glucosyltransferase involved in O-antigen modification of Shigella flexneri serotype 1c

The O antigen of serotype 1c differs from the unmodified O antigen of serotype Y by the addition of a disaccharide (two glucosyl groups) to the tetrasaccharide repeating unit. It was shown here that addition of the first glucosyl group is mediated by th

Shigella flexneri serotype 1c derived from serotype 1a by acquisition of gtrIC gene cluster via a bacteriophage

BACKGROUND: Shigella spp. are the primary causative agents of bacillary dysentery. Since its emergence in the late 1980s, the S. flexneri serotype 1c remains poorly understood, particularly with regard to its origin and genetic evolution. This article provides a molecular insight into this novel serotype and the gtrIC gene cluster that determines its unique immune recognition. RESULTS: A PCR of the gtrIC cluster showed that serotype 1c isolates from different geographical origins were genetically conserved. An analysis of sequences flanking the gtrIC cluster revealed remnants of a prophage genome, in particular integrase and tRNAPro genes. Meanwhile, Southern blot analyses on serotype 1c, 1a and 1b strains indicated that all the tested serotype 1c strains may have had a common origin that has since remained distinct from the closely related 1a and 1b serotypes. The identification of prophage genes upstream of the gtrIC cluster is consistent with the notion of bacteriophage-mediated integration of the gtrIC cluster into a pre-existing serotype. CONCLUSIONS: This is the first study to show that serotype 1c isolates from different geographical origins share an identical pattern of genetic arrangement, suggesting that serotype 1c strains may have originated from a single parental strain. Analysis of the sequence around the gtrIC cluster revealed a new site for the integration of the serotype converting phages of S. flexneri. Understanding the origin of new pathogenic serotypes and the molecular basis of serotype conversion in S. flexneri would provide information for developing cross-reactive Shigella vaccines

Differential Host Immune Responses to Epidemic and Endemic Strains of Shigella dysenteriae Type 1

Shigella dysenteriae type 1 causes devastating epidemics in developing countries with high case-fatality rates in all age-groups. The aim of the study was to compare host immune responses to epidemic (T2218) and endemic strains of S. dysenteriae type 1. Shigellacidal activity of serum from rabbits immunized with epidemic or endemic strains, S. dysenteriae type 1-infected patients, and healthy adult controls from Shigella endemic and non-endemic regions was measured. Immunogenic cross-reactivity of antibodies against Shigella antigens was evaluated by Western blot analysis. Oxidative burst and phagocytic responses of monocytes and neutrophils to selected S. dysenteriae type 1 strains were assessed by flow cytometry. Rabbit antisera against epidemic strain were less effective in killing heterologous bacteria compared to endemic antisera (p=0.0002). Patients showed an increased serum shigellacidal response after two weeks of onset of diarrhoea compared to the acute stage (3-4 days after onset) against their respective homologous strains; the response against T2218 and heterologous endemic S. dysenteriae type 1 strains was not significant. The serum shigellacidal response against all the S. dysenteriae type 1 strains was similar among healthy controls from endemic and non-endemic regions and was comparable with the acute stage response by patients. Compared to endemic strains of S. dysenteriae type 1, T2218 was significantly resistant to phagocytosis by both monocytes and neutrophils. No obvious differences were obtained in the induction of oxidative burst activity and cathelicidin-mediated killing. Cross-reactivity of antibody against antigens present in the epidemic and endemic strains showed some differences in protein/peptide complexity and intensity by Western blot analysis. In summary, epidemic T2218 strain was more resistant to antibody-mediated defenses, namely phagocytosis and shigellacidal activity, compared to endemic S. dysenteriae type 1 strains. Part of this variation may be attributed to the differential complexity of protein/peptide antigens

<i>Campylobacter jejuni</i> HS:23 and Guillain-Barré Syndrome, Bangladesh

To the Editor: Guillain-Barré syndrome (GBS) is an acute peripheral neuropathy triggered by a preceding infectious illness. Gastroenteritis caused by Campylobacter jejuni is the most frequently reported antecedent event. In Japan, South Africa, China, and Mexico, Campylobacter strains with certain Penner heat-stable (HS) serotypes, including HS:19 and HS:41, are overrepresented among isolates from GBS case-patients, compared with isolates from enteritis case-patients. Several studies indicate that C. jejuni HS:19 and HS:41 have a clonal population structure and suggest that these serotypes might have unique virulence properties that are intricately linked to development of GBS. However, data from the United Kingdom and the Netherlands suggest that such virulence properties may not be restricted to specific HS serotypes because many other serotypes can be cultured from patients with GBS (5). We report a non-HS:19 and non-HS:41 C. jejuni serotype and sequence type (ST)–3219 that are overrepresented among isolates from GBS patients in Bangladesh. [...

<i>Campylobacter jejuni</i> HS:23 and Guillain-Barré Syndrome, Bangladesh

To the Editor: Guillain-Barré syndrome (GBS) is an acute peripheral neuropathy triggered by a preceding infectious illness. Gastroenteritis caused by Campylobacter jejuni is the most frequently reported antecedent event. In Japan, South Africa, China, and Mexico, Campylobacter strains with certain Penner heat-stable (HS) serotypes, including HS:19 and HS:41, are overrepresented among isolates from GBS case-patients, compared with isolates from enteritis case-patients. Several studies indicate that C. jejuni HS:19 and HS:41 have a clonal population structure and suggest that these serotypes might have unique virulence properties that are intricately linked to development of GBS. However, data from the United Kingdom and the Netherlands suggest that such virulence properties may not be restricted to specific HS serotypes because many other serotypes can be cultured from patients with GBS (5). We report a non-HS:19 and non-HS:41 C. jejuni serotype and sequence type (ST)–3219 that are overrepresented among isolates from GBS patients in Bangladesh. [...

Differential Host Immune Responses to Epidemic and Endemic Strains of Shigella dysenteriae Type 1

Shigella dysenteriae type 1 causes devastating epidemics in developing countries with high case-fatality rates in all age-groups. The aim of the study was to compare host immune responses to epidemic (T2218) and endemic strains of S. dysenteriae type 1. Shigellacidal activity of serum from rabbits immunized with epidemic or endemic strains, S. dysenteriae type 1-infected patients, and healthy adult controls from Shigellaendemic and non-endemic regions was measured. Immunogenic cross-reactivity of antibodies against Shigella antigens was evaluated by Western blot analysis. Oxidative burst and phagocytic responses of monocytes and neutrophils to selected S. dysenteriae type 1 strains were assessed by flow cytometry. Rabbit antisera against epidemic strain were less effective in killing heterologous bacteria compared to endemic antisera (p=0.0002). Patients showed an increased serum shigellacidal response after two weeks of onset of diarrhoea compared to the acute stage (3-4 days after onset) against their respective homologous strains; the response against T2218 and heterologous endemic S. dysenteriae type 1 strains was not significant. The serum shigellacidal response against all the S. dysenteriae type 1 strains was similar among healthy controls from endemic and non-endemic regions and was comparable with the acute stage response by patients. Compared to endemic strains of S. dysenteriae type 1, T2218 was significantly resistant to phagocytosis by both monocytes and neutrophils. No obvious differences were obtained in the induction of oxidative burst activity and cathelicidin-mediated killing. Cross-reactivity of antibody against antigens present in the epidemic and endemic strains showed some differences in protein/peptide complexity and intensity by Western blot analysis. In summary, epidemic T2218 strain was more resistant to antibody-mediated defenses, namely phagocytosis and shigellacidal activity, compared to endemic S. dysenteriae type 1 strains. Part of this variation may be attributed to the differential complexity of protein/peptide antigens

Campylobacter jejuni HS:23 and Guillain-Barré Syndrome, Bangladesh

To the Editor: Guillain-Barré syndrome (GBS) is an acute peripheral neuropathy triggered by a preceding infectious illness. Gastroenteritis caused by Campylobacter jejuni is the most frequently reported antecedent event. In Japan, South Africa, China, and Mexico, Campylobacter strains with certain Penner heat-stable (HS) serotypes, including HS:19 and HS:41, are overrepresented among isolates from GBS case-patients, compared with isolates from enteritis case-patients. Several studies indicate that C. jejuni HS:19 and HS:41 have a clonal population structure and suggest that these serotypes might have unique virulence properties that are intricately linked to development of GBS. However, data from the United Kingdom and the Netherlands suggest that such virulence properties may not be restricted to specific HS serotypes because many other serotypes can be cultured from patients with GBS (5). We report a non-HS:19 and non-HS:41 C. jejuni serotype and sequence type (ST)–3219 that are overrepresented among isolates from GBS patients in Bangladesh. [...

A Multicentre Study of Shigella Diarrhoea in Six Asian Countries: Disease Burden, Clinical Manifestations, and Microbiology

BACKGROUND: The burden of shigellosis is greatest in resource-poor countries. Although this diarrheal disease has been thought to cause considerable morbidity and mortality in excess of 1,000,000 deaths globally per year, little recent data are available to guide intervention strategies in Asia. We conducted a prospective, population-based study in six Asian countries to gain a better understanding of the current disease burden, clinical manifestations, and microbiology of shigellosis in Asia. METHODS AND FINDINGS: Over 600,000 persons of all ages residing in Bangladesh, China, Pakistan, Indonesia, Vietnam, and Thailand were included in the surveillance. Shigella was isolated from 2,927 (5%) of 56,958 diarrhoea episodes detected between 2000 and 2004. The overall incidence of treated shigellosis was 2.1 episodes per 1,000 residents per year in all ages and 13.2/1,000/y in children under 60 months old. Shigellosis incidence increased after age 40 years. S. flexneri was the most frequently isolated Shigella species (1,976/2,927 [68%]) in all sites except in Thailand, where S. sonnei was most frequently detected (124/146 [85%]). S. flexneri serotypes were highly heterogeneous in their distribution from site to site, and even from year to year. PCR detected ipaH, the gene encoding invasion plasmid antigen H in 33% of a sample of culture-negative stool specimens. The majority of S. flexneri isolates in each site were resistant to amoxicillin and cotrimoxazole. Ciprofloxacin-resistant S. flexneri isolates were identified in China (18/305 [6%]), Pakistan (8/242 [3%]), and Vietnam (5/282 [2%]). CONCLUSIONS: Shigella appears to be more ubiquitous in Asian impoverished populations than previously thought, and antibiotic-resistant strains of different species and serotypes have emerged. Focusing on prevention of shigellosis could exert an immediate benefit first by substantially reducing the overall diarrhoea burden in the region and second by preventing the spread of panresistant Shigella strains. The heterogeneous distribution of Shigella species and serotypes suggest that multivalent or cross-protective Shigella vaccines will be needed to prevent shigellosis in Asia

Clonality, virulence and antimicrobial resistance of enteroaggregative Escherichia coli from Bangladesh

Enteroaggregative E. coli (EAEC) is a global cause of gastrointestinal infection yet little is known about the virulence or antimicrobial resistance (AMR) of EAEC in regions of the world where diarrhoeal disease is most common. In Bangladesh diarrhoeal disease is one of the leading causes of mortality and extensive case control studies have linked specific EAEC clonal complexes with pathogenic potential