Decrease in shigellosis-related deaths without Shigella spp.-specific interventions, Asia

Changing trends in the prevalence of Shigella species: emergence of multi-drug resistant Shigella sonnei biotype g in Bangladesh

Shigellosis, caused by Shigella species, is a major public health problem in Bangladesh. To determine the prevalence and distribution of different Shigella species, we analyzed 10,827 Shigella isolates from patients between 2001 and 2011. S. flexneri was the predominant species isolated throughout the period. However, the prevalence of S. flexneri decreased from 65.7% in 2001 to 47% in 2011, whereas the prevalence of S. sonnei increased from 7.2% in 2001 to 25% in 2011. S. boydii and S. dysenteriae accounted for 17.3% and 7.7% of the isolates respectively throughout the period. Of 200 randomly selected S. sonnei isolates for extensive characterization, biotype g strains were predominant (95%) followed by biotype a (5%). Resistance to commonly used antibiotics including trimethoprim-sulfamethoxazole, nalidixic acid, ciprofloxacin, mecillinam and ampicillin was 89.5%, 86.5%, 17%, 10.5%, and 9.5%, respectively. All isolates were susceptible to ceftriaxone, cefotaxime, ceftazidime and imipenem. Ninety-eight percent of the strains had integrons belonging to class 1, 2 or both. The class 1 integron contained only dfrA5 gene, whereas among class 2 integron, 16% contained dhfrAI-sat1-aadA1-orfX gene cassettes and 84% harbored dhfrA1-sat2 gene cassettes. Plasmids of ∼5, ∼1.8 and ∼1.4 MDa in size were found in 92% of the strains, whereas only 33% of the strains carried the 120 MDa plasmid. PFGE analysis showed that strains having different integron patterns belonged to different clusters. These results show a changing trend in the prevalence of Shigella species with the emergence of multidrug resistant S. sonnei. Although S. flexneri continues to be the predominant species albeit with reduced prevalence, S. sonnei has emerged as the second most prevalent species replacing the earlier dominance by S. boydii and S. dysenteriae in Bangladesh.

Antimicrobial resistance of Shigella spp. from humans in Shanghai, China, 2004-2011

A retrospective study conducted on patients with diarrhea in Shanghai, China from 2004-2011, indicated that of 77,600 samples collected, 1,635 (2.1%) tested positive for Shigella. Species isolated included S. sonnei (1,066, 65.1%), S. flexneri (569, 34.7%), and S. boydii (3, 0.2%). Most of the Shigella isolates were found to be resistant to streptomycin (98.7%), trimethoprim (98.0%), ampicillin (92.1%), and nalidixic acid (91.7%). Additionally, many isolates were resistant to tetracycline (86.9%), trimethoprim + sulfamethoxazole (80.1%), sulfisoxazole (76.8%) and gentamicin (55.5%). Approximately 80% of the isolates were resistant to at least eight antimicrobial agents, 14% to at least ten antimicrobials tested and 10 isolates to fourteen antimicrobials, including sulfonamides, fluoroquinolones, tetracyclines, aminoglycosides and β-lactamases. Importantly, co-resistance to fluoroquinolones and the third- and fourth-generation cephalosporins was also identified. The high levels of resistance to antimicrobial agents commonly used in clinical medicine presents a great challenge to treating patients with shigellosis.

Conventional and molecular investigation of Shigella isolates in relation to an outbreak in the area of Isfahan, Iran

BACKGROUND AND OBJECTIVE

Over 165 million cases of shigellosis occur in the world each year, mostly in developing countries. Outbreaks of shigellosis are associated with poor sanitation, natural calamities, contaminated food and crowded living conditions. In late summer 2006, during the final stage of an outbreak of shigellosis at a vast region of Isfahan province, Naein & Ardestan, our laboratory was assigned to investigate the outbreak in order to determine the causative agent.

MATERIALS AND METHODS

A total of 146 rectal swabs which had been collected from the patients by local laboratories on separate days were screened using a battery of conventional and molecular tests.

RESULTS

Thirteen specimens tested positive for Shigella spp. They were identified as S. sonnei (6, 46.1%), S. dysenteriae (4, 30.8%), S. flexneri (2, 15.4%) and Shigella spp (1, 7.7%) by conventional and molecular microbiological tests. According to ribotyping results the isolates were grouped into 3 distinct clusters encompassing the majority of isolates and a single line of descent representing isolate S122 which was nonreactive with any Shigella polyvalent antisera.

CONCLUSION

This diarrheal outbreak appeared to be the result of shigellosis. Despite the fact that Shigella sonnei was the predominant organism isolated from patients, the causative agent of outbreak diarrhea remains obscure, since other Shigella species were also involved. The serologic testing supports this conclusion, as do the molecular patterns of the Shigella isolates. Having considered the time of investigation which was in the late stage of the outbreak, it was very likely that a collection of endemic and epidemic clinical samples was screened resulting in isolation of various Shigella species.

Dynamics of shigellosis epidemics: estimating individual-level transmission and reporting rates from national epidemiologic data sets

Shigellosis, a diarrheal disease, is endemic worldwide and is responsible for approximately 15,000 laboratory-confirmed cases in the United States every year. However, patients with shigellosis often do not seek medical care. To estimate the burden of shigellosis, we extended time-series susceptible-infected-recovered models to infer epidemiologic parameters from underreported case data. We applied the time-series susceptible-infected-recovered-based inference schemes to analyze the largest surveillance data set of Shigella sonnei in the United States from 1967 to 2007 with county-level resolution. The dynamics of shigellosis transmission show strong annual and multiyear cycles, as well as seasonality. By using the schemes, we inferred individual-level parameters of shigellosis infection, including seasonal transmissibilities and basic reproductive number (R0). In addition, this study provides quantitative estimates of the reporting rate, suggesting that the shigellosis burden in the United States may be more than 10 times the number of laboratory-confirmed cases. Although the estimated reporting rate is generally under 20%, and R0 is generally under 1.5, there is a strong negative correlation between estimates of the reporting rate and R0. Such negative correlations are likely to pose identifiability problems in underreported diseases. We discuss complementary approaches that might further disentangle the true reporting rate and R0.

Recent advances in understanding enteric pathogenic Escherichia coli

Although Escherichia coli can be an innocuous resident of the gastrointestinal tract, it also has the pathogenic capacity to cause significant diarrheal and extraintestinal diseases. Pathogenic variants of E. coli (pathovars or pathotypes) cause much morbidity and mortality worldwide. Consequently, pathogenic E. coli is widely studied in humans, animals, food, and the environment. While there are many common features that these pathotypes employ to colonize the intestinal mucosa and cause disease, the course, onset, and complications vary significantly. Outbreaks are common in developed and developing countries, and they sometimes have fatal consequences. Many of these pathotypes are a major public health concern as they have low infectious doses and are transmitted through ubiquitous mediums, including food and water. The seriousness of pathogenic E. coli is exemplified by dedicated national and international surveillance programs that monitor and track outbreaks; unfortunately, this surveillance is often lacking in developing countries. While not all pathotypes carry the same public health profile, they all carry an enormous potential to cause disease and continue to present challenges to human health. This comprehensive review highlights recent advances in our understanding of the intestinal pathotypes of E. coli.

Antibiotics for the treatment of Cholera, Shigella and Cryptosporidium in children

Background

Diarrhea is a major contributor to the burden of morbidity and mortality in children; it accounts for a median of 11% of all deaths among children aged less than 5 years, amounting to approximately 0.8 million deaths per year. Currently there is a dearth of literature exploring the effectiveness of antibiotics for diarrhea due to Cholera, Shigella and cryptosporidiosis in children.

Methods

We reviewed the literature reporting the effect of antibiotics for the treatment of diarrhea due to Cholera, Shigella and Cryptosporidium in children under five years. We used a standardized abstraction and grading format and performed meta-analyses to determine the effect of the treatment with various antibiotics on mortality and rates of clinical and bacteriological/parasitological failure. The CHERG Standard Rules were applied to determine the final effect of treatment with antibiotics on diarrhea morbidity and mortality.

Results

For Cholera; the evidence was weak to recommend any effect on mortality. For Shigella; there was no data on mortality; either all-cause or cause specific, hence we used clinical failure rates as a proxy for Shigella deaths and propose that treatment of Shigella dysentery with antibiotics can result in a 82% reduction in diarrhea mortality due to Shigella. For cryptosporidiosis; there was data on all-cause mortality but the evidence was weak hence we used clinical failure rates as a proxy for mortality to estimate that antimicrobial treatment of diarrhea due to cryptosporidiosis can result in a 54% reduction in mortality.

Conclusions

There is evidence to recommend antibiotic use for reduction of morbidity and mortality due to Cholera, Shigella and Cryptosporidium. We recommend that more clinical trials should be conducted to evaluate the efficacy and safety of first- and second- line drugs currently in use for treatment for diarrhea and dysentery in both developing and developed countries.

Global causes of diarrheal disease mortality in children <5 years of age: a systematic review

Estimation of pathogen-specific causes of child diarrhea deaths is needed to guide vaccine development and other prevention strategies. We did a systematic review of articles published between 1990 and 2011 reporting at least one of 13 pathogens in children <5 years of age hospitalized with diarrhea. We included 2011 rotavirus data from the Rotavirus Surveillance Network coordinated by WHO. We excluded studies conducted during diarrhea outbreaks that did not discriminate between inpatient and outpatient cases, reporting nosocomial infections, those conducted in special populations, not done with adequate methods, and rotavirus studies in countries where the rotavirus vaccine was used. Age-adjusted median proportions for each pathogen were calculated and applied to 712 000 deaths due to diarrhea in children under 5 years for 2011, assuming that those observed among children hospitalized for diarrhea represent those causing child diarrhea deaths. 163 articles and WHO studies done in 31 countries were selected representing 286 inpatient studies. Studies seeking only one pathogen found higher proportions for some pathogens than studies seeking multiple pathogens (e.g. 39% rotavirus in 180 single-pathogen studies vs. 20% in 24 studies with 5–13 pathogens, p<0·0001). The percentage of episodes for which no pathogen could be identified was estimated to be 34%; the total of all age-adjusted percentages for pathogens and no-pathogen cases was 138%. Adjusting all proportions, including unknowns, to add to 100%, we estimated that rotavirus caused 197 000 [Uncertainty range (UR) 110 000–295 000], enteropathogenic E. coli 79 000 (UR 31 000–146 000), calicivirus 71 000 (UR 39 000–113 000), and enterotoxigenic E. coli 42 000 (UR 20 000–76 000) deaths. Rotavirus, calicivirus, enteropathogenic and enterotoxigenic E. coli cause more than half of all diarrheal deaths in children <5 years in the world.

Comparison of clinical and laboratory characteristics of intestinal amebiasis with shigellosis among patients visiting a large urban diarrheal disease hospital in Bangladesh

Between 1993 and 2011, a total of 371 intestinal amebiasis (IA), caused by Entamoeba histolytica cases were compared with 1,113 shigellosis (randomly selected) patients of icddr,b, excluding co-infections (rotavirus and Vibrio cholerae) in two age stratums: 0-14 years of age and ≥ 15 years of age. The number of IA and shigellosis cases gradually reduced over the study period. In multivariate analysis, individuals 0-14 years of age, slum dwellers (odds ratio [OR] 3.51; 95% confidence interval [CI] 1.69-7.24; P < 0.001), red blood cell (0.44 [0.24-0.86] 0.016), fecal leukocytes (0.17 [0.07-0.33] < 0.001), and alkaline stool (0.16 [0.07-0.36] < 0.001) were independently associated with IA; and among individuals ≥ 15 years of age, living in the slum area (1.88 [1.12-3.14] 0.016), watery stool (2.21 [1.37-3.55] 0.001), use of antimicrobials before visiting hospital (0.67 [0.46-0.99] 0.047), red blood cell (0.45 [0.22-0.94] 0.036), and fecal leukocytes (0.21 [0.12-0.35] < 0.001) in stool were independently associated with IA. Socio-demographic and clinical characteristics of IA and shigellosis varied distantly from each other.

Identification and characterization of a novel Shigella flexneri serotype Yv in China

Shigella flexneri is the major cause of bacterial shigellosis in developing countries. S. flexneri is divided into at least 19 serotypes, the majority of which are modifications of the same basic O-antigen by glucosylation and/or O-acetylation of its sugar residues by phage encoded serotype-converting genes. Recently, a plasmid encoded phosphoethanolamine (PEtN) modification of the O-antigen has been reported, which is responsible for the presence of the MASF IV-1 determinant and results in conversion of traditional serotypes X, 4a and Y to novel serotypes Xv, 4av and Yv, respectively. In this study, we characterized 19 serotype Yv strains isolated in China. A variant of the O-antigen phosphoethanolamine transferase gene opt (formerly called lpt-O) carried by a pSFxv_2-like plasmid was found in serotype Yv strains, which specifies the phosphorylation pattern on the O-antigen of this serotype. For the majority of the O-antigen units, the PEtN modification occurs on Rha^III, while for a minority, modifications occur on both Rha^II and Rha^III. Serotype-specific gene detection and PFGE analysis suggested that these serotype Yv isolates were originated from serotypes Y, Xv and 2a by acquisition of an opt-carrying plasmid and/or inactivation of serotype-specific gene gtrII or gtrX. These data, combined with those of serotypes Xv and 4av reported earlier, demonstrate that the plasmid-encoded PEtN modification is an important serotype conversion mechanism in S. flexneri, in addition to glucosylation and O-acetylation.

Using complete genome comparisons to identify sequences whose presence accurately predicts clinically important phenotypes

In clinical settings it is often important to know not just the identity of a microorganism, but also the danger posed by that particular strain. For instance, Escherichia coli can range from being a harmless commensal to being a very dangerous enterohemorrhagic (EHEC) strain. Determining pathogenic phenotypes can be both time consuming and expensive. Here we propose a simple, rapid, and inexpensive method of predicting pathogenic phenotypes on the basis of the presence or absence of short homologous DNA segments in an isolate. Our method compares completely sequenced genomes without the necessity of genome alignments in order to identify the presence or absence of the segments to produce an automatic alignment of the binary string that describes each genome. Analysis of the segment alignment allows identification of those segments whose presence strongly predicts a phenotype. Clinical application of the method requires nothing more that PCR amplification of each of the set of predictive segments. Here we apply the method to identifying EHEC strains of E. coli and to distinguishing E. coli from Shigella. We show in silico that with as few as 8 predictive sequences, if even three of those predictive sequences are amplified the probability of being EHEC or Shigella is >0.99. The method is thus very robust to the occasional amplification failure for spurious reasons. Experimentally, we apply the method to screening a set of 98 isolates to distinguishing E. coli from Shigella, and EHEC from non-EHEC E. coli strains and show that all isolates are correctly identified.

Recent progress towards development of a Shigella vaccine

The burden of dysentery due to shigellosis among children in the developing world is still a major concern. A safe and efficacious vaccine against this disease is a priority, since no licensed vaccine is available. This review provides an update of vaccine achievements focusing on subunit vaccine strategies and the forthcoming strategies surrounding this approach. In particular, this review explores several aspects of the pathogenesis of shigellosis and the elicited immune response as being the basis of vaccine requirements. The use of appropriate Shigella antigens, together with the right adjuvants, may offer safety, efficacy and more convenient delivery methods for massive worldwide vaccination campaigns.

Gastrointestinal and extra-intestinal manifestations of childhood shigellosis in a region where all four species of Shigella are endemic

Objective

To determine the clinical manifestations and outcome of shigellosis among children infected with different species of Shigella.

Methods

We identified all patients <15 years infected with Shigella admitted to the icddr, b Dhaka hospital during one year. Study staff reviewed admission records and repeated the physical examinations and history of patients daily.

Results

Of 792 children with shigellosis 63% were infected with S. flexneri, 20% with S. dysenteriae type 1, 10% with S. boydii, 4% with S. sonnei, and 3% with S. dysenteriae types 2–10. Children infected with S. dysenteriae type 1, when compared to children infected with other species, were significantly (P<0.05) more likely to have severe gastrointestinal manifestations: grossly bloody stools (78% vs. 33%), more stools in the 24 h before admission (median 25 vs. 11), and rectal prolapse (52% vs. 15%) - and extra-intestinal manifestations - leukemoid reaction (22% vs. 2%), hemolytic-uremic syndrome (8% vs. 1%), severe hyponatremia (58% vs. 26%) and neurologic abnormalities (24% vs. 16%). The overall fatality rate was 10% and did not differ significantly by species. In a multiple regression analysis young age, malnutrition, hyponatremia, lesser stool frequency, documented seizure, and unconsciousness were predictive of death.

Conclusions

Both severe intestinal disease and extra-intestinal manifestations of shigellosis occur with infection by any of the four species of Shigella, but are most common with S. dysenteriae type 1. Among these inpatient children, the risk of death was high with infection of any of the four Shigella species.

O-antigen structure of Shigella flexneri serotype Yv and effect of the lpt-O gene variation on phosphoethanolamine modification of S. flexneri O-antigens

Shigella flexneri is the major human pathogen causing shigellosis. O-antigens of all S. flexneri serotypes (except for serotype 6) share the →2)-α-l-Rhap(III)-(1 → 2)-α-l-Rhap(II)-(1 → 3)-α-l-Rhap(I)-(1 → 3)-β-d-GlcpNAc-(1→ basic O-unit, whereas differences between the serotypes are conferred by phage-encoded glucosylation and/or O-acetylation at various positions. Recently, in serotype X and 4a variants called Xv and 4av, respectively, O-antigen modification with phosphoethanolamine (PEtN) has been identified, which is encoded by a plasmid-borne gene (lpt-O) for a PEtN-transferase and confers the monoclonal antibody IV-1(MASF IV-1) determinant to the bacteria. In this study, we elucidated the O-antigen structure of serotype Yv, another MASF IV-1-positive novel variant of S. flexneri. The serotype Yv O-antigen has the same basic carbohydrate backbone structure as that of the "classical" serotype Y, but differs in the presence of PEtN at position 3 of Rha(III) (major) or both Rha(II) and Rha(III) (minor). This pattern is similar to that of serotype 4av, but different from the pattern of serotype Xv, which is characterized by major PEtN modification on Rha(II). In serotype Yv, mono- and bisphosphorylated O-units generate a block-copolymeric structure, the former being partially O-acetylated at position 6 of GlcNAc and the latter lacking O-acetylation. Functional analysis revealed a correlation between the serotype-specific PEtN modification pattern and the lpt-O variation in different serotypes: lpt-O(RII) in serotype Xv is better tuned for phosphorylation of Rha(II) and lpt-O(RIII) in serotypes Yv and 4av for phosphorylation of Rha(III). These data enhance our knowledge of S. flexneri serotype conversion mechanisms and help to understand the biosynthesis process of the new O-antigen variants.

Causative species and serotypes of shigellosis in mainland China: systematic review and meta-analysis

BACKGROUND

Shigella, the causative agent of shigellosis, is a major global public health concern, particularly in developing countries with poor sanitation. A comprehensive and current understanding of the prevalent species and serotypes of shigellosis is essential for both disease prevention and vaccine development. However, no current data are available on the causative species/serotypes of shigellosis in mainland China during the past decade.

METHODS AND FINDINGS

Relevant studies addressing the prevalent species of shigellosis in mainland China from January 2001 to December 2010 were identified from PubMed and the Chinese BioMedical Literature Database (in Chinese) until April 2012. A total of 131 eligible articles (136 studies) were included in this review. Meta-analyses showed that the prevalences of S. flexneri and S. sonnei were 76.2% (95% CI, 73.7%-78.5%) and 21.3% (95% CI, 19.0%-23.7%), respectively. Stratified analyses indicated a decrease in the prevalence of S. flexneri cases and an increase in the prevalence of S. sonnei cases concurrent with the rapid economic growth experienced by China in recent years. Moreover, significantly higher rates of S. sonnei were observed in the East, North and Northeast regions of China, as compared to the rest of the country. These phenomena imply the possible association between the prevalent species of Shigella and regional economic status; however, additional factors also exist and require further investigations. Moreover, the two major serotypes S. flexneri 2a and 4c accounted for 21.5% (95% CI, 16.7%-27.4%) and 12.9% (95% CI 9.8%-16.9%) of S. flexneri infections, respectively, in the past decade. However, these results were found to be frequently heterogeneous (p for Q tests <0.01).

CONCLUSIONS

This study provides an updated review of the causative agents of shigellosis in mainland China and focuses on the importance of strengthening prevention and research efforts on S. sonnei and the newly emerged S. flexneri serotype 4c.

Identification of a divergent O-acetyltransferase gene oac 1b from Shigella flexneri serotype 1b strains

Shigella flexneri is a leading cause of bacterial dysentery in developing countries. Among the 15 known serotypes, four (1b, 3a, 3b and 4b) contain a group 6 epitope due to an acetyl group connected to the O-2 position of rhamnose III on the tetrasaccharide structure of the lipopolysaccharide. O-acetyltransferase encoded by a bacteriophage, Sf6, mediates the acetylation reaction. We found that the oac gene in serotype 1b strains was very different from that in serotypes 3a, 3b and 4b strains and is herein after referred to as oac_1b which shares with oac 88%–89% identity at the DNA level and 85% identity at the protein level. Considering that S. flexneri strains of serotypes 1–5 share a recent common ancestry, the divergent oac_1b is more likely to have been obtained from outside S. flexneri than to have undergone rapid divergence from the oac gene in the other serotypes (3a, 3b and 4b) within S. flexneri. The cloned oac_1b gene was found to perform the same acetylation function as oac. Analysis of the genomic regions flanking oac_1b showed that it was present in a prophage on the chromosome and the organizational structure is different from that of phage Sf6. Additionally, phage conversion assay showed that serotype 1b cannot be generated by infecting serotype 1a strains with Sf6. We conclude that oac_1b was carried by a non-Sf6 phage and is uniquely present in serotype 1b.

Emergence of a novel Shigella flexneri serotype 1d in China

We report on the isolation of 5 Shigella flexneri strains displaying a novel serotype, 1d, that shares serologic features from both S. flexneri serotypes 1a and X. The 1d strains contained serotype-converting bacteriophages SfI and SfX in tandem on the chromosome. These strains were likely originated from serotype X strains through SfI infection.

Efficacy of sodium butyrate adjunct therapy in shigellosis: a randomized, double-blind, placebo-controlled clinical trial

BACKGROUND

Treatment of shigellosis in rabbits with butyrate reduces clinical severity and counteracts the downregulation of cathelicidin (CAP-18) in the large intestinal epithelia. Here, we aimed to evaluate whether butyrate can be used as an adjunct to antibiotics in the treatment of shigellosis in patients.

METHODS

A randomized, double-blind, placebo-controlled, parallel-group designed clinical trial was conducted. Eighty adult patients with shigellosis were randomized to either the Intervention group (butyrate, n = 40) or the Placebo group (normal saline, n = 40). The Intervention group was given an enema containing sodium butyrate (80 mM), twice daily for 3 days, while the Placebo group received the same dose of normal saline. The primary endpoint of the trial was to assess the efficacy of butyrate in improving clinical, endoscopic and histological features of shigellosis. The secondary endpoint was to study the effect of butyrate on the induction of antimicrobial peptides in the rectum. Clinical outcomes were assessed and concentrations of antimicrobial peptides (LL-37, human beta defensin1 [HBD-1] and human beta defensin 3 [HBD-3]) and pro-inflammatory cytokines (interleukin-1β [IL-1β] and interleukin-8 [IL-8]) were measured in the stool. Sigmoidoscopic and histopathological analyses, and immunostaining of LL-37 in the rectal mucosa were performed in a subgroup of patients.

RESULTS

Compared with placebo, butyrate therapy led to the early reduction of macrophages, pus cells, IL-8 and IL-1β in the stool and improvement in rectal histopathology. Butyrate treatment induced LL-37 expression in the rectal epithelia. Stool concentration of LL-37 remained significantly higher in the Intervention group on days 4 and 7.

CONCLUSION

Adjunct therapy with butyrate during shigellosis led to early reduction of inflammation and enhanced LL-37 expression in the rectal epithelia with prolonged release of LL-37 in the stool.

TRIAL REGISTRATION

ClinicalTrials.gov, NCT00800930.

The patient presenting with acute dysentery--a systematic review

OBJECTIVES

The etiologies, clinical presentations and diagnosis of acute pathogen-specific dysentery in children and adults in industrialized and developing regions is described to help develop recommendations for therapy.

METHODS

We conducted a systematic review of literature published between January 2000 and June 2011 to determine the frequency of occurrence of pathogen-specific dysentery.

RESULTS

Shigella, Salmonella, and Campylobacter remain the most frequent bacterial causes of dysentery worldwide. Shiga toxin-producing Escherichia coli (STEC) is potentially important in industrialized countries. Entamoeba histolytica must be considered in the developing world, particularly in rural or periurban areas. Clinicians should use epidemiological clues and knowledge of endemicity to suspect Vibrio spp., Aeromonas spp., Plesiomonas spp., Yersinia enterocolitica, Clostridium difficile, Cytomegalovirus or Schistosoma mansoni in cases presenting with dysentery. A single fecal sample studied for etiologic agents is the customary way to make an etiologic diagnosis.

CONCLUSIONS

While a majority of dysenteric cases will not have an identifiable agent causing the illness, when an etiologic organism is identified, other than STEC, each has a specific recommended form of therapy, which is provided in this review.

Genesis of a novel Shigella flexneri serotype by sequential infection of serotype-converting bacteriophages SfX and SfI

Background

Shigella flexneri is the major pathogen causing bacillary dysentery. Fifteen serotypes have been recognized up to now. The genesis of new S. flexneri serotypes is commonly mediated by serotype-converting bacteriophages. Untypeable or novel serotypes from natural infections had been reported worldwide but have not been generated in laboratory.

Results

A new S. flexneri serotype-serotype 1 d was generated when a S. flexneri serotype Y strain (native LPS) was sequentially infected with 2 serotype-converting bacteriophages, SfX first and then SfI. The new serotype 1 d strain agglutinated with both serotype X-specific anti-7;8 grouping serum and serotype 1a-specific anti- I typing serum, and differed from subserotypes 1a, 1b and 1c. Twenty four S. flexneri clinical isolates of serotype X were all converted to serotype 1 d by infection with phage SfI. PCR and sequencing revealed that SfI and SfX were integrated in tandem into the proA-yaiC region of the host chromosome.

Conclusions

These findings suggest a new S. flexneri serotype could be created in nature. Such a conversion may be constrained by susceptibility of a strain to infection by a given serotype-converting bacteriophage. This finding has significant implications in the emergence of new S. flexneri serotypes in nature.

Acute infectious diarrhea

Infectious diarrhea is both a local and a global concern. Illnesses can range from mild inconveniences to life-threatening epidemics. Although diarrhea can be caused by a vast array of pathogens, the cornerstone of prevention is provision of a safe food and water supply, application of basic hygiene principles, and the development and administration of vaccines. The cornerstone of treatment is rehydration. Selection of specific antimicrobial therapy should be based on disease presentation and epidemiologic factors.

Epidemiology and molecular mechanism of integron-mediated antibiotic resistance in Shigella

Integrons are gene capture and expression systems that are characterized by the presence of an integrase gene. This encodes an integrase, a recombined site, and a promoter. They are able to capture gene cassettes from the environment and incorporate them using site-specific recombination. The role of integrons and gene cassettes in the dissemination of multidrug resistance in Gram-negative bacteria is significant. In Shigella species, antimicrobial resistance is often associated with the presence of class 1 and class 2 integrons that contain resistance gene cassettes. Multiple and complex expression regulation mechanisms involving mobile genetic elements in integrons have been developed in the evolution of Shigella strains. Knowledge of the epidemiology and molecular mechanisms of antimicrobial resistance in this important pathogen is essential for the implementation of intervention strategies. This review was conducted to introduce the structures and functions of integrons in Shigella species and mechanisms that control integron-mediated events linked to antibiotic resistance.

Genetic characteristics and changing antimicrobial resistance among Shigella spp. isolated from hospitalized diarrhoeal patients in Kolkata, India

To study the prevalence pattern and trends in the phenotypic and genetic characteristics of shigellae, we tested 212 isolates isolated from diarrhoeal patients admitted to the Infectious Diseases Hospital, Kolkata, India, from November 2007 to October 2010. Prevalence of Shigella spp. was higher in the >5 years age group (69 %) than in children in the <5 years age group (31 %). Serotypes 2a, 3a and untypable isolates of Shigella flexneri were frequently detected. An increase in the isolation of Shigella sonnei (15 %) is a novel trend in this region. Fluoroquinolone resistance among S. flexneri serotypes 2a, 3a and other serogroups of shigellae is another evolving trend. The set gene was exclusively present in S. flexneri 2a, and the sen gene was detected in all serogroups. PFGE revealed the grouping of S. flexneri isolates according to their serotypes with approximately 80-100 % similarity, whilst Shigella dysenteriae type 2 and S. sonnei were clonal in nature. There was no demarcation in the prevalence of serotypes, antimicrobial resistance or clonality between the two age groups.

Whole-genome phylogeny of Escherichia coli/Shigella group by feature frequency profiles (FFPs)

A whole-genome phylogeny of the Escherichia coli/Shigella group was constructed by using the feature frequency profile (FFP) method. This alignment-free approach uses the frequencies of l-mer features of whole genomes to infer phylogenic distances. We present two phylogenies that accentuate different aspects of E. coli/Shigella genomic evolution: (i) one based on the compositions of all possible features of length l = 24 (∼8.4 million features), which are likely to reveal the phenetic grouping and relationship among the organisms and (ii) the other based on the compositions of core features with low frequency and low variability (∼0.56 million features), which account for ∼69% of all commonly shared features among 38 taxa examined and are likely to have genome-wide lineal evolutionary signal. Shigella appears as a single clade when all possible features are used without filtering of noncore features. However, results using core features show that Shigella consists of at least two distantly related subclades, implying that the subclades evolved into a single clade because of a high degree of convergence influenced by mobile genetic elements and niche adaptation. In both FFP trees, the basal group of the E. coli/Shigella phylogeny is the B2 phylogroup, which contains primarily uropathogenic strains, suggesting that the E. coli/Shigella ancestor was likely a facultative or opportunistic pathogen. The extant commensal strains diverged relatively late and appear to be the result of reductive evolution of genomes. We also identify clade distinguishing features and their associated genomic regions within each phylogroup. Such features may provide useful information for understanding evolution of the groups and for quick diagnostic identification of each phylogroup.