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

Shigellosis in Taiwan: An old enteric pathogen with changing epidemiology and increasing antimicrobial resistance

While the incidence of shigellosis has decreased in developed nations due to improved living conditions and healthcare systems, it remains prevalent in economically developing regions. In recent years, a resurgence of shigellosis has been observed in the United States, Europe, and Taiwan, primarily among men having sex with men and people living with human immunodeficiency virus, along with a rise in antimicrobial resistance. This study aims to review the historical epidemiological trends and drug resistance in shigellosis, with a focus on Taiwan. A comprehensive search was conducted using various databases and sources, including non-English literature in Japanese and Chinese. In developed countries, Shigella sonnei and Shigella flexneri are the most common species, while Shigella dysenteriae infections are sporadic. In Taiwan, the classification and prevalence of Shigella species have evolved over time, with S. flexneri and S. sonnei being the predominant strains. Fluoroquinolone resistance and azithromycin non-susceptibility are the ongoing threat. In conclusion, shigellosis remains a significant global health concern, with recent increases in certain populations and antimicrobial resistance. Further research is necessary to understand the clinical significance and risk factors associated with asymptomatic carriers and to assess the impact of behavioral modifications and interventions in high-risk populations.

Production of highly immunogenic and safe Triton X-100 produced bacterial ghost vaccine against Shigella flexneri 2b serotype

BACKGROUND

Bacterial ghost cells (BGCs) are cells were drained of their genetic and cytoplasmic components. This work aimed to develop vaccine candidates against the Shigella flexneri (S. flexneri) 2b serotype using the BGCs approach. For the first time, (S. flexneri) 2b serotype BGCs vaccine was prepared by incubation with Triton X-100 (TX100) for only 12 h. Its safety and immunogenicity were compared to another vaccine produced using a previously used surfactant, namely Tween 80 (TW80). Scanning electron microscopy (SEM), cellular DNA, protein contents measurements, and ghost cell re-cultivation were used to confirm the successful generation of the BGCs. Immunogenicity was assessed through mice's intraperitoneal (IP) immunization followed by infection with S. flexneri ATCC 12022. Finally, histopathological examination was carried out.

RESULTS

Viable colony forming units (CFUs) of S. flexneri were counted from stool samples as well as homogenized colon tissues of the non-immunized challenged group. Immunized mice sera showed a significant increase in serum bactericidal activity of both preparations (TX100 = 40% and TW80 = 56%) compared to the non-immunized challenged group (positive control). The IgG levels of the bacterial ghost-vaccinated groups were four and three times greater for the TX100 and TW80 ghost vaccines, respectively, compared to that of the positive control; both bacterial ghost vaccines (BGVs) were safe and effective, according to the results of the safety check tests and histopathological analysis.

CONCLUSIONS

When comparing the BGVs prepared using TX100 and TW80 methods, the use of TX100 as a new chemical treating agent for BGC production attained robust results in terms of shorter incubation time with the targeted cells and a strong immune response against S. flexneri 2b serotype ATCC 12022 in the IP challenge test. However, a clinical study is needed to confirm the efficacy and total safety of this novel vaccine.

A Shigella sonnei clone with extensive drug resistance associated with waterborne outbreaks in China

Antimicrobial resistance of Shigella sonnei has become a global concern. Here, we report a phylogenetic group of S. sonnei with extensive drug resistance, including a combination of multidrug resistance, coresistance to ceftriaxone and azithromycin (cef^Razi^R), reduced susceptibility to fluoroquinolones, and even colistin resistance (col^R). This distinct clone caused six waterborne shigellosis outbreaks in China from 2015 to 2020. We collect 155 outbreak isolates and 152 sporadic isolates. The cef^Razi^R isolates, including outbreak strains, are mainly distributed in a distinct clade located in global Lineage III. The outbreak strains form a recently derived monophyletic group that may have emerged circa 2010. The cef^Razi^R and col^R phenotypes are attributed to the acquisition of different plasmids, particularly the IncB/O/K/Z plasmid coharboring the bla_CTX-M-14, mphA, aac(3)-IId, dfrA17, aadA5, and sul1 genes and the IncI2 plasmid with an mcr-1 gene. Genetic analyses identify 92 accessory genes and 60 single-nucleotide polymorphisms associated with the cef^Razi^R phenotype. Surveillance of this clone is required to determine its dissemination and threat to global public health.

Prevalence of Multidrug-Resistant and Extended-Spectrum Beta-Lactamase-Producing Shigella Species in Asia: A Systematic Review and Meta-Analysis

Shigellosis remains one of the leading causes of morbidity and mortality worldwide and is the second leading cause of diarrheal mortality among all age groups. However, the global emergence of antimicrobial-resistant Shigella strains, limiting the choice of effective drugs for shigellosis, has become the major challenge in the treatment of Shigella infections. The aim of this systematic review and meta-analysis was to provide an updated picture of the prevalence of antimicrobial-resistant Shigella species in Asia. A comprehensive and systematic search was performed on three electronic databases (PubMed, ScienceDirect and Scopus), in which 63 eligible studies published between 2010 and 2022 were identified. From our meta-analysis of proportions using a random-effects model, the overall prevalence of Shigella spp. in Asian patients was estimated to be 8.0% (95% CI: 5.5–10.5). The pooled prevalence rates of multidrug-resistant (MDR) and extended-spectrum beta-lactamase (ESBL)-producing Shigella strains were 68.7% (95% CI: 59.9–77.5) and 23.9% (95% CI: 12.9–34.8), respectively. Concerning recommended antimicrobial drugs for Shigella, the prevalence of resistance was highest for ciprofloxacin (29.8%) and azithromycin (29.2%), followed by ceftriaxone (23.8%), in spite of their importance as first- and second-line treatments for shigellosis. In contrast, resistance to carbapenems, such as ertapenem (0.0%), imipenem (0.1%) and meropenem (0.0%), was almost non-existent among the 49 tested antibiotics. The significantly high prevalence estimation suggests that the multidrug-resistant Shigella is a pressing threat to public health worthy of careful and justified interventions. Effective antibiotic treatment strategies, which may lead to better outcomes for the control and treatment of shigellosis in Asia, are essential.

Controlled Human Infection Models To Accelerate Vaccine Development

The timelines for developing vaccines against infectious diseases are lengthy, and often vaccines that reach the stage of large phase 3 field trials fail to provide the desired level of protective efficacy. The application of controlled human challenge models of infection and disease at the appropriate stages of development could accelerate development of candidate vaccines and, in fact, has done so successfully in some limited cases. Human challenge models could potentially be used to gather critical information on pathogenesis, inform strain selection for vaccines, explore cross-protective immunity, identify immune correlates of protection and mechanisms of protection induced by infection or evoked by candidate vaccines, guide decisions on appropriate trial endpoints, and evaluate vaccine efficacy. We prepared this report to motivate fellow scientists to exploit the potential capacity of controlled human challenge experiments to advance vaccine development. In this review, we considered available challenge models for 17 infectious diseases in the context of the public health importance of each disease, the diversity and pathogenesis of the causative organisms, the vaccine candidates under development, and each model's capacity to evaluate them and identify correlates of protective immunity. Our broad assessment indicated that human challenge models have not yet reached their full potential to support the development of vaccines against infectious diseases. On the basis of our review, however, we believe that describing an ideal challenge model is possible, as is further developing existing and future challenge models.

Decreased Susceptibility of Shigella Isolates to Azithromycin in Children in Tehran, Iran

Azithromycin (AZT) has widely been used for the treatment of shigellosis in children. Recent studies showed a high rate of decreased susceptibility to azithromycin due to different mechanisms of resistance in Shigella isolates. Accordingly, the purpose of this study was to investigate the role of azithromycin resistance mechanisms of Shigella isolates in Iran during a two-year period. In this study, we investigated the mechanisms of resistance among Shigella spp. that were isolated from children with shigellosis. The minimum inhibitory concentration (MIC) of Shigella isolates to azithromycin was determined by the agar dilution method in the presence and absence of Phe-Arg-β-naphthylamide inhibitor. The presence of 12 macrolide resistance genes was investigated for all isolates by PCR for the first time in Tehran province in Iran. Among the 120 Shigella spp., only the mph(A) gene (49.2%) was detected and other macrolide resistance genes were absent. The phenotypic activity of efflux pump was observed in 1.9% of isolates which were associated with over expression of both omp(A) and omp(W) genes. The high prevalence of the mph(A) gene among DSA isolates may indicate that azithromycin resistance has evolved as a result of antimicrobial selection pressures and inappropriate use of azithromycin.

Shigella Outer Membrane Vesicles as Promising Targets for Vaccination

The clinical symptoms of shigellosis, a gastrointestinal infection caused by Shigella spp. range from watery diarrhea to fulminant dysentery. Endemic infections, particularly among children in developing countries, represent the majority of clinical cases. The situation is aggravated due to the high mortality rate of shigellosis, the rapid dissemination of multi-resistant Shigella strains and the induction of only serotype-specific immunity. Thus, infection prevention due to vaccination, encompassing as many of the circulating serotypes as possible, has become a topic of interest. However, vaccines have turned out to be ineffective so far. Outer membrane vesicles (OMVs) are promising novel targets for vaccination. OMVs are constitutively secreted by Gram-negative bacteria including Shigella during growth. They are composed of soluble luminal portions and an insoluble membrane and can contain toxins, bioactive periplasmic and cytoplasmic (lipo-) proteins, (phospho-) lipids, nucleic acids and/or lipopolysaccharides. Thus, OMVs play an important role in bacterial cell–cell communication, growth, survival and pathogenesis. Furthermore, they modulate the secretion and transport of biomolecules, the stress response, antibiotic resistance and immune responses of the host. Thus, OMVs serve as novel secretion machinery. Here, we discuss the current literature and highlight the properties of OMVs as potent vaccine candidates because of their immunomodulatory, antigenic and adjuvant properties.

Therapeutic target identification via differential genome analysis of antibiotic resistant Shigella sonnei and inhibitor evaluation against a selected drug target

Shigella sonnei has been implicated in bloody diarrhea (accompanied by abdominal pain and fever) and is an emerging pathogen of concern, especially in developing countries. The major means of transmission is the fecal-oral route while sexual transmission has also been reported. In children, the impact might be stunted growth due to life-threatening illness. Resistance has been reported in this species for several types of antibiotics. In this study, we retrieved the antibiotic-resistant labeled whole genome sequences of the species from the PATRIC database and performed a pan-genome analysis to filter out core genes. Antibiotic resistance was studied in the core, accessory and unique genome. Core genes were utilized as seed substance for essentiality analysis and drug candidate assignment. Product of the gene aroG, i.e. chorismate biosynthetic process 3-deoxy-7-phosphoheptulonate synthase enzyme, responsible for aromatic amino acid family biosynthetic process, was taken for further downstream processing. Natural product libraries of flavonoids (n = 178), ZINC database derived inhibitor compounds of the 3-deoxy-7-phosphoheptulonate synthase enzyme (n = 112), and streptomycin compounds (n = 737) were docked to find out potent inhibitors, followed by dynamics simulation of 50 ns each for top compounds.. Physicochemical and ADMET profiling of the top compounds was done to analyze their safety for consumption. We propose that the top compounds: Phytoene from Streptomycin library and ZINC000036444158 (synonym:1,16-bis[(dihydroxyphosphinyl)oxy]hexadecane) from 3-deoxy-7-phosphoheptulonate synthase inhibitor library of ZINC database (and used as a control in this study) should be tested in vitro against Shigella sonnei, to fully determine their efficacy. This could add to the drying pipeline of potent drug molecules against emerging pathogens.

Effect of temperature and its interaction with other meteorological factors on bacillary dysentery in Jilin Province, China

Bacterial dysentery (BD) brings a major disease burden to developing countries. Exploring the influence of temperature and its interaction with other meteorological factors on BD is significant for the prevention and early warning of BD in the context of climate change. Daily BD cases and meteorological data from 2008 to 2018 were collected in all nine prefecture-level cities in Jilin Province. A one-stage province-level model and a two-stage city-specific multivariate meta-pooled level distributed lag non-linear model were established to explore the correlation between temperature and BD, then the weather-stratified generalised additive model was used to test the interaction. During the study period, a total of 26 971 cases of BD were developed. The one-stage and two-stage cumulative dose-response ‘J’ curves overlapped, and results showed a positive correlation between temperature and BD with a 1–6 days lag effect. Age group ⩾5 years was found to be more sensitive to the effects. Moreover, there was a significant interaction between temperature, humidity and precipitation (P = 0.004, 0.002, respectively) on BD under high temperature (>0 °C), reminding residents and policymakers to pay attention to the prevention of BD in situations with both high temperature and humidity, high temperature and precipitation during the temperate monsoon climate.

Laboratory-based surveillance of Shigella spp. from human clinical cases in Colombia, 1997-2018

INTRODUCTION

Shigellosis is endemic in low-and middle-income countries, causing approximately 125 million episodes of diarrhea and leading to approximately 160 .000 deaths annually one-third of which is associated with children.

OBJECTIVE

To describe the characteristics and antimicrobial resistance profiles of Shigella species recovered in Colombia from 1997 to 2018.

MATERIALS AND METHODS

We received isolates from laboratories in 29 Colombian departments. We serotyped with specific antiserum and determined antimicrobial resistance and minimal inhibitory concentrations for ten antibiotics with Kirby-Bauer tests following the Clinical and Laboratory Standards Institute recommendations.

RESULTS

We analyzed 5,251 isolates of Shigella spp., most of them obtained from stools (96.4%); 2,511 (47.8%) were from children under five years of age. The two most common species were S. sonnei (55.1%) and S. flexneri (41.7%). The highest resistance rate was that of tetracycline (88.1%) followed by trimethoprim-sulfamethoxazole (79.3%) and ampicillin (65.5%); 50.8% of isolates were resistant to chloramphenicol, 43.6% to amoxicillin/clavulanic acid, and less than 1% to cefotaxime, ceftazidime, gentamicin, and ciprofloxacin. In S. sonnei, the most common resistance profile corresponded to trimethoprim-sulfamethoxazole (92%) whereas in S. flexneri the most common antibiotic profiles were multidrug resistance.

CONCLUSIONS

In Colombia, children under five years are affected by all Shigella species. These findings should guide funders and public health officials to make evidence based decisions for protection and prevention measures. The antimicrobial resistance characteristics found in this study underline the importance of combating the dissemination of the most frequently isolated species, S. sonnei and S. flexneri.

Virulence-Related Gene Distribution Among Shigella Isolates in Anhui, China: The Association with Antimicrobial Resistance

Objective

The aim of this study was to investigate the antimicrobial resistance profiles and distribution of virulence-related genes (VRGs) among Shigella isolates in Anhui, China, and to identify the correlation between the VRGs and antimicrobial resistance.

Materials and Methods

A total of 525 non-duplicate Shigella isolates (449 S. flexneri, 68 S. sonnei, 3 S. boydii, and 5 S. dysenteriae) were collected in Anhui Province, China between September 2011 and September 2015. The antimicrobial resistance of the strains was determined by the agar dilution method according to CLSI guidelines. The presence of 16 VRGs, including ipaH, ipaA-D, ial, virB, virF, set, sen, icsA, icsB, sigA, sat, pic, and sepA, was evaluated using PCR amplification and sequencing.

Results

Shigella flexneri was the most abundant (85.5%), followed by S. sonnei (13.0%). The proportion of males with S. flexneri was higher than that of females (57% vs 43%; P<0.0001). The most common resistance pattern was the combination of ampicillin, nalidixic acid, and tetracycline for S. flexneri (90.2%) and S. sonnei (94.1%). Resistance to ciprofloxacin and levofloxacin was more common among S. flexneri than among S. sonnei (49.7% vs.19.1%, P<0.0001; 30.5% vs 10.3%, P=0.001, respectively). All the isolates were positive for the ipaH gene, while the set, sat, pic, and sepA genes were not detected among the S. sonnei isolates. Except for sigA and sen, resistance to chloramphenicol and ciprofloxacin was more common among VRG-positive S. flexneri than among VRG-negative S. flexneri (P<0.05). Furthermore, resistance to ceftriaxone and ceftazidime was more frequently detected among sat- and set-positive S. flexneri than among sat- and set-negative S. flexneri (P<0.05). However, gentamicin resistance was more prevalent among VRG-negative (ial, virF, set, sat, pic, and sepA) S. flexneri than among VRG-positive S. flexneri (P<0.05).

Conclusion

Shigella flexneri remains the predominant species in Anhui, China, and the resistance to fluoroquinolones was more widespread among S. flexneri than among S. sonnei. Shigella flexneri strains harboring specific VRGs were associated with antimicrobial resistance. To the best of our knowledge, this is the first report of the correlation between the VRGs and antimicrobial resistance in Anhui, China.

Prevalence and antimicrobial profile of Shigella isolates in a tertiary care hospital of North Karnataka: A 12-year study

Context

Shigella is a common cause of bacillary dysentery. Although it is reported worldwide, the majority of the infections are seen in developing countries with Shigella flexneri being the most common isolate. Prevalence of Shigella species and their antibiotic susceptibility profiles vary according to geographic area and season.

Aims

In the present study, the epidemiology and antimicrobial profile of Shigella from stool samples received at our hospital for a period of 12 years (January 2006 to December 2017) was evaluated.

Subjects and Methods

A total of 4578 stool samples were collected from the cases of acute gastroenteritis and diarrhoea. Samples were processed for culture and sensitivity according to standard microbiological techniques. The presumptive identification of Shigella species was done using standard conventional biochemical tests and confirmed using antisera.

Results

A total of 189 (4.2%) samples yielded Shigella spp. Isolation of Shigella spp. were more frequent from males (58.2%). S. flexneri was the commonest species isolated (47.6%) followed by Shigella sonnei(11.6%), Shigella dysenteriae (4.2%) and Shigella boydii (2.1%). Non-typeable Shigella was commonly recovered. The isolates showed high resistance to ampicillin (76.7%) and co-trimoxazole (75%) while highest susceptibility was observed to ceftriaxone (79.2%).

Conclusions

S. flexneri was the most prevalent species isolated at this centre. Shigella isolates from the study showed alarming resistance to recommended antibiotics. Non-typeable Shigella accounted for 34.4% isolates. Molecular discrimination between Shigella and Escherichia coli is essential.

Prevalence of Shigella species and its drug resistance pattern in Ethiopia: a systematic review and meta-analysis

BACKGROUND

Shigella species are a major cause of dysentery and may attribute for death worldwide. Currently antibiotic resistance became the critical challenges for management of infectious disease. The aim was to conduct a systematic review and meta-analysis of Shigella species and its drug resistance pattern in Ethiopia.

METHODS

A comprehensive literature search was conducted through internet searches using database of MEDLINE, PubMed, Google scholar, EMBASE, HINARI, Cochrane Library and reference lists of previous prevalence studies from January 1999 to November 2018. Results were presented in forest plot, tables and figures with 95% CI. The Cochrane Q test and I2 test statistic were used to test heterogeneity across studies. The Pooled estimate of Shigella species and its drug resistance pattern was computed by a random effects model.

RESULTS

The pooled prevalence of Shigella species in Ethiopia was 6.6% (95% CI 4.7-8.8). In the subgroup analysis, the highest prevalence was observed among patients in Health facility (8.5%, 95% CI 6.2-11.5) whereas the lowest prevalence was observed in Community based studies (1.6%, 95% CI 0.8-3.4). In addition, Shigella species were highly resistant to ampicillin, amoxicillin, erythromycin and multi-drug resistant (MDR) with the pooled resistance proportions of 83.1% (95% CI 75.7-88.6), 84.1% (95% CI 75.6-90.1), 86.5% (95% CI 70.9-94.4) and 83.2% (95% CI 77.1-87.9), respectively. On the other hand, comparably low resistance pattern was reported for ciprofloxacin 8.9% (95% CI 6.0-12.8), ceftriaxone 9.3% (95% CI 3.9-20.5), and norfloxacin 8.2% (95% CI 3.8-16.6) and gentamycin 17.3% (95% CI 11.2-25.9). Subgroup analyses indicated that study years were associated with a decreasing Shigella prevalence over time (p = 0.002).

CONCLUSION

The pooled estimate showed high burden of Shigella infection and its high proportion of drug resistance pattern to ampicillin, amoxicillin and erythromycin in Ethiopia. Therefore, initiating and scale up of performing drug susceptibility test for each shigellosis case, educate the community and health care providers on appropriate use of antibiotics need to be considered and strengthened.

Antimicrobial resistance and genetic characterization of Shigella spp. in Shanxi Province, China, during 2006-2016

Background

Shigella spp., facultative anaerobic bacilli of the family Enterobacteriaceae, are one of the most common causes of diarrheal diseases in human worldwide which have become a significant public health burden. So, we aimed to analyze the antimicrobial phenotypes and to elucidate the molecular mechanisms underlying resistance to cephalosporins and fluoroquinolones in Shigella isolates from patients with diarrhea in Shanxi Province.

Results

During 2006–2016, we isolated a total of 474 Shigella strains (including 337 S. flexneri and 137 S. sonnei). The isolates showed high rates of resistance to traditional antimicrobials, and 26, 18.1 and 3.0% of them exhibited resistance to cephalosporins, fluoroquinolones and co-resistance to cephalosporins and fluoroquinolones, respectively. Notably, 91.1% of these isolates, including 22 isolates that showed an ACTSuT profile, exhibited multidrug resistance (MDR). The resistance rates to cephalosporins in S. sonnei isolates were higher than those in S. flexneri. Conversely, the resistance rates to fluoroquinolones were considerably higher in S. flexneri isolates. Among the 123 cephalosporins-resistant isolates, the most common extended-spectrum beta-lactamase gene was bla_TEM-1, followed by bla_CTX-M, bla_OXA-1, and bla_SHV-12. Six subtypes of bla_CTX-M were identified, bla_CTX-M-14 (n = 36) and bla_CTX-M-55 (n = 26) were found to be dominant. Of all the 86 isolates with resistance to fluoroquinolones and having at least one mutation (Ser83Leu, His211Tyr, or Asp87Gly) in the the quinolone resistance-determining regions of gyrA, 79 also had mutation of parC (Ser80Ile), whereas 7 contained plasmid-mediated quinolone resistance genes including qnrA, qnrB, qnrS, and aac(60)-Ib-cr. Furthermore, pulsed-field gel electrophoresis analysis (PFGE) showed a considerable genetic diversity in S. flexneri isolates. However, the S. sonnei isolates had a high genetic similarity.

Conclusions

Coexistence of diverse resistance genes causing the emergence and transmission of MDR might render the treatment of shigellosis difficult. Therefore, continuous surveillance might be needed to understand the actual disease burden and provide guidance for shigellosis.

Electronic supplementary material

The online version of this article (10.1186/s12866-019-1495-6) contains supplementary material, which is available to authorized users.

Prevalence and characterisation of third-generation cephalosporin-resistant Shigella flexneri isolates from Jiangsu Province, China, 2013-2015

OBJECTIVES

The aim of this study was to assess the prevalence of Shigella flexneri resistance to third-generation cephalosporins (3GCs) and to characterise the underlying resistance mechanisms.

METHODS

A total of 282 S. flexneri strains isolated in 2013-2015 in Jiangsu Province, China, were identified, serotyped and analysed for their susceptibility to 3GCs. The bla_TEM, bla_SHV, bla_OXA-1-like and bla_CTX-M-type extended-spectrum β-lactamase (ESBL) genes were amplified and sequenced by PCR.

RESULTS

Of the 282 S. flexneri strains, 97 (34.4%) were resistant to cefotaxime, from which 68 (24.1%) were also resistant to ceftazidime. ESBL genes were detected in 73/97 isolates (75.3%), of which 66/73 (90.4%) showed resistance to 3GCs. Of the 73 ESBL-positive isolates, 32 (43.8%) were positive for CTX-M-1 group (17 for CTX-M-55, 4 for CTX-M-3, 1 for CTX-M-15, 3 for CTX-M-79 and 7 for CTX-M-123), 31 (42.5%) were positive for CTX-M-9 group (29 for CTX-M-14, 1 for CTX-M-24 and 1 for CTX-M-27), 25 (34.2%) were positive for TEM-types (21 for TEM-1 and 4 for TEM-1b) and 1 (1.4%) was positive for SHV-type (SHV-12); none were positive for CTX-M-2 group, CTX-M-8 group and OXA-type.

CONCLUSION

ESBLs play an important role in Shigella resistance to 3GCs. CTX-M-14 and CTX-M-55 appeared to be the dominant ESBLs in 13 cities of Jiangsu Province. Therefore, it is time to regularly monitor resistance of S. flexneri to 3GCs and to take appropriate measures to manage this problem.

Bacterial pathogen spectrum of acute diarrheal outpatients in an urbanized rural district in Southwest China

OBJECTIVES

To conduct a one-year pathogen surveillance of acute diarrheal disease based on outpatient clinics in township hospitals in rural Hongta District of Yunnan Province, China.

METHODS

Fecal specimens of acute diarrhea cases and relevant epidemiological information were collected. Salmonella, Shigella, Vibrio, Aeromonas, Plesiomonas shigelloides and diarrheogenic Escherichia coli (DEC) were examined.

RESULTS

Among the 797 stool specimens sampled, 198 samples (24.8%) were positive in pathogen isolation, and 223 strains were isolated. The order of isolation rates from high to low were DEC, Aeromonas, P. shigelloides, Salmonella, Shigella and Vibrio. The overall positive rate in middle school students and preschool children was relatively high; while the overall positive rate of less than 1-year-old infants and above 55 years olds was relatively low. The isolates were analyzed by pulsed-field gel electrophoresis (PFGE). Some cases had the same or very close onset time, and the isolates had similar PFGE patterns, suggesting a possible outbreak once occurred but was not detected by the current infectious disease reporting system.

CONCLUSIONS

Pathogen infection and transmission in rapidly urbanized rural areas is a serious issue. There is a great need for a more sensitive and accurate mode of monitoring, reporting and outbreak identification of diarrheal disease.

Antibiotic resistance and molecular characterization of shigella isolates recovered from children aged less than 5 years in Manhiça, Southern Mozambique

The objective of this study was to assess antibiotic resistance and the molecular epidemiology of shigella isolates from a case-control study of diarrhoea, conducted from 2007 to 2012 in children aged less than 5 years in Manhiça district, southern Mozambique. All isolates were tested for antimicrobial susceptibility using the disc diffusion method. Polymerase chain reaction was used to detect different molecular mechanisms of antibiotic resistance. Serotyping was performed using specific antisera. The clonal relationship of Shigella flexneri and Shigella sonnei was assessed by pulsed-field gel electrophoresis (PFGE). Of the 67 shigella isolates analysed, 59 were diarrhoeal cases and eight were controls. S. flexneri (70.1%; 47/67) was the most common species, followed by S. sonnei (23.9%; 16/67). The most prevalent S. flexneri serotypes were 2a (38.3%; 18/47), 6 (19.2%; 9/47) and 1b (14.9%; 7/47). High rates of antimicrobial resistance were observed for trimethoprim-sulfametoxazole (92.5%; 62/67), tetracycline (68.7%; 46/67), chloramphenicol (53.7%; 36/67) and ampicillin (50.7%; 34/67). Multi-drug resistance (MDR) was present in 55.2% (37/67) of the isolates and was associated with a case fatality rate of 8.1% (3/37). PFGE revealed 22 clones (16 S. flexneri and 6 S. sonnei), among which P1 (31.9%; 15/47), P9 (17%; 8/47) and P2 (10.6%; 5/47) were the most prevalent clones of S. flexneri. In conclusion, S. flexneri was the most prevalent species, with MDR isolates mainly belonging to three specific clones (P1, P9 and P2). The case fatality rate observed among MDR isolates is a matter of concern, indicating the need for appropriate treatment.

Newest data on fluoroquinolone resistance mechanism of Shigella flexneri isolates in Jiangsu Province of China

Background

To determine the prevalence, antimicrobial susceptibility patterns and related presence of mutations in quinolone resistance-determining region (QRDR) genes and plasmid-mediated quinolone resistance (PMQR) among Shigella flexneri isolates obtained from Jiangsu Province, China.

Methods

A total of 400 Shigella flexneri clinical isolates collected during 2012–2015 were identified by biochemical and serological methods, and the antimicrobial susceptibility pattern was evaluated using the disc-diffusion method. PCR and DNA sequencing were accomplished to identify mutations in gyrA, gyrB, parC and parE, and the presence of qnrA, qnrB, qnrC, qnrD, qnrS, qepA and aac(6′)-Ib-cr genes were also detected.

Results

Of all the Shigella flexneri, 75.8% were resistant to nalidixic acid, and 37.0% were categorized as norfloxacin resistant. Overall, 75.5% of isolates possessed gyrA mutations (Ser83Leu, Asp87Gly/Asn and His211Tyr), while 84.3% had parC mutations (Ser80Ile, Ala81Pho, Gln91His and Ser129Pro). The most prevalent point mutations in gyrA and parC were Ser83Leu (75.5%, 302/400) and Ser80Ile (74.5%, 298/400), relatively. Besides, the Gln517Arg alternation in gyrB was detected in 13 S. flexneri isolates and no mutations were identified in parE. PMQR determinations of qnrB, qnrS and aac(6′)-Ib-cr were detected among 16 strains (4.0%).

Conclusions

The results presented here show that fluoroquinolone resistance in these clinical isolates result from mutations in chromosome, besides, despite the low prevalence of PMQR determinants in Jiangsu, it is essential to continue surveillance PMQR determinants in this area.

First report of the qnrA determinant in Shigella sonnei isolated from China

We investigated the first presence of qnrA among Shigella sonnei clinical isolates in Jiangsu Province, China. The qnrA-positive isolates coexisted with the mutation in gyrA at codon 83, these isolates were resistant to nalidixic acid and 22·2% (2 of 9) of them were resistant to norfloxacin.

Novel mutations in gyrA and parC among Shigella sonnei strains from Jiangsu Province of China, 2002-2011

BACKGROUND

To investigate fluoroquinolone resistance and associated mechanisms of Shigella sonnei isolates in Jiangsu Province of China between 2002 and 2011.

METHODS

All 337 unduplicated S. sonnei isolates were collected from hospitals in Jiangsu Province from January 2002 to December 2011. Fluoroquinolone susceptibility was characterized by Kirby-Bauer disk diffusion method, and direct nucleotide sequencing of genes of the quinolone resistance determining regions were conducted. Also, the transferable quinolone resistance determinants, including qnrA, qnrB, qnrC, qnrD, qnrS, aac-(6')-Ib-cr and qepA were amplified by PCR.

RESULTS

Among 950 Shigella isolates, 337 (35.5%) were identified as S. sonnei, of which 76.6% displayed nalidixic acid resistance and norfloxacin-resistant isolates appeared in 2005-2009, with an average resistance rate of 21.8%. Commonly reported point mutations of Ser83Leu and Asp87Asn/Gly in gyrA and Ser80Ile in parC were detected, with mutation rates of 78.0%, 9.5% and 30.3%, respectively, while no alteration in gyrB or parE were detected. Besides, His211Tyr mutation in gyrA was first reported in a S. sonnei strain in 2009 and two novel mutations in parC were found, of which Met86Trp occurred in another strain in 2009 and Ser129Pro appeared every year except 2011 (28.8%). Plasmid-mediated quinolone resistance determinants were found in 23 isolates and 19 of these isolates were resistant to both nalidixic acid and norfloxacin. qnrB, qnrS, aac-(6')-Ib-cr and qepA were detected in 1, 7, 14 and 2 S. sonnei strains, relatively, and the most abundant PMQR gene found in this work was aac-(6')-Ib-cr (4.2%).

INTERPRETATION & CONCLUSIONS

S. sonnei became increasingly important as fluoroquinolone-resistant isolates emerged, and further detection on the resistant genes would be useful in the treatment and control of this infection.

An outbreak of shigellosis in a Children Welfare Institute caused by a multiple-antibiotic-resistant strain of Shigella flexneri 2a

From September 1 to October 27, 2015, an outbreak of bacillary dysentery occurred in the Shenzhen Children Welfare Institute (SCWI). The shigellosis was uncommon in Shenzhen and no related outbreak was reported during the last 5 years. An epidemiological investigation was conducted and the children and nursing workers in SCWI were surveyed for gastrointestinal symptoms; 28 of children reported having a diarrheal illness. Rectal swabs or fecal specimens from 14 case patients and 24 nursing workers or cook, as well as 17 swabs from implicated items were collected and examined for Shigella, Vibrio parahaemolyticus, and Salmonella. Susceptibility testing and pulse-field gel electrophoresis (PFGE) were performed on the Shigella isolates. The multiple-antibiotic-resistant Shigella flexneri 2a was isolated from 10 ill children aged less than 5 years. The source of the outbreak was most likely a new welfare child transferred from an institute in another county and the secondary transmission of the illness was facilitated by the limited activity space and the cohabiting of ill and well residents. The outbreak was controlled after quarantine of ill residents, introduction of new antibiotics and the improvements of hygienic condition. This was the first time that shigellosis outbreak was reported at such settings in Shenzhen and the results of this investigation underscored the need for adequate precautions to prevent secondary transmission of multiple-antibiotic-resistant strain in the welfare setting.

Update on: Shigella new serogroups/serotypes and their antimicrobial resistance

Shigellosis represents a major burden of disease in developing countries. A low infectious dose allows the disease to be spread effectively. Although shigellosis is mostly a self-limiting disease, antibiotics are recommended to reduce deaths, disease symptoms and organism-shedding time. However, in India, antimicrobial resistance among the genus Shigella is more common than among any other enteric bacteria. Notably, new serotypes or subserotypes in Shigella are reported from various parts of the world. Identification of new subserotypes of Shigella spp. is becoming a major issue as these strains are nontypeable by conventional serotyping. The commercially available antisera may not cover all possible epitopes of the O lipopolysaccharide antigen of Shigella serotypes. Therefore, molecular methods which most closely approach the resolution of full serotyping are necessary to identify such strains. In addition, the knowledge of a prevalent serotype in various geographic regions may assist in formulating strategies such as the development of a vaccine to prevent infection especially when the immunity to disease is serotype specific, and to understand the disease burden caused by new Shigella serotypes.

Decreased Susceptibility to Azithromycin Among Clinical Shigella Isolates from China

The aim of this study was to detect the decreased susceptibility to azithromycin (DSA) and associated mechanisms in Shigella from China. Three hundred and ninety-two Shigella isolates, including 134 Shigella flexneri and 258 Shigella sonnei isolates, were examined for minimum inhibitory concentrations (MICs) and zone sizes to azithromycin by broth microdilution and disk diffusion methods, respectively. The MICs were compared with corresponding zone diameters to find whether there was uniformity between both tests. Twelve macrolide-resistant genes located on mobile elements were determined for the DSA isolates by PCR, and chromosomal efflux pump activity was analyzed using Phe-Arg-β-naphthylamide inhibition test and quantitative real-time PCR. Shigella isolates displayed MICs of 0.125-512 μg/ml and zone sizes of 6-26 mm against azithromycin. There were 80 (20.4%) isolates to be DSA. No significant difference was found between the DSA rates of S. flexneri and S. sonnei isolates (p = 0.052). There was an intimate relativity between MICs and zone diameters (p < 0.001). Only the plasmid-borne mphA conferring high-level DSA was detected in 55.0% (44/80) DSA-Shigella isolates. This study highlighted the prevalence of DSA-Shigella and mphA in the region studied. Clinical laboratories and clinicians should pay attention to the elevated azithromycin MICs in Shigella spp.

Molecular characterization and analysis of high-level multidrug-resistance of Shigella flexneri serotype 4s strains from China

To conduct the first comprehensive analysis of Shigella flexneri serotype 4s, a novel serotype found in 2010, we identified 24 serotype 4s isolates from 1973 shigellosis cases in China (2002–2014). The isolates were characterized by single nucleotide polymorphism (SNP) phylogenetic analysis, pulsed-field gel electrophoresis (PFGE) and multilocus sequence typing (MLST) to determine their genetic relatedness, and analysed further for their antimicrobial susceptibilities and antimicrobial resistance determinants. The PFGE and SNP phylogenetic analyses suggest that S. flexneri serotype 4s strains are derived from multiple serotypes, including two predominant serotypes in China: serotype X variant and serotype II. Three new sequence types were identified by MLST. All isolates were resistant to ticarcillin, ampicillin and tetracycline, with high-level resistance to third-generation cephalosporins. Notably, all the isolates were multidrug resistant (MDR), with the highest levels of resistance observed for eight antimicrobials classes. Most isolates contain various antimicrobial resistance determinants. In conclusion, we found that serotype 4s isolates have multiple evolutionary sources, diverse biochemical characteristics and genomes, and highly prevalent multidrug resistance and antimicrobial-resistant determinants. With few clinical treatment options, continuous monitoring and timely intervention against this emerging MDR serotype is essential. The possibility that serotype 4s will become the next predominant serotype exists.

Prevalence, resistance patterns, and characterization of integrons of Shigella flexneri isolated from Jiangsu Province in China, 2001-2011

OBJECTIVE

To provide the epidemiology, resistance pattern, and characterization of integrons in Shigella flexneri isolated between 2001 and 2011 in Jiangsu Province.

METHOD

A total of 624 strains of S. flexneri were collected from both outpatients and inpatients in hospitals in Jiangsu Province from January 2001 to December 2011. The Kirby-Bauer disk diffusion method was used to perform the antimicrobial susceptibility test. Polymerase chain reaction (PCR) was used in the detection of integrons. Pulsed-field gel electrophoresis (PFGE) was applied in the homology studies.

RESULT

Serotype 2a accounted for the largest proportion in S. flexneri, namely 26.4 %. Notably, an increasing trend was detected in the resistance to common antimicrobial agents during the period 2001-2011. In recent years, more than 80.0 % isolates of S. flexneri have proved to be resistant to ampicillin, nalidixic acid, and tetracycline. The positive rates of class 1, class 2, and the atypical class 1 integrons in S. flexneri are 69.3 %, 87.8 %, and 89.2 % respectively. Most integrons detected in our research carry genes encoding resistance to trimethoprim and streptomycin.

CONCLUSION

Antimicrobial resistance in S. flexneri has demonstrated a continuous rising trend in Jiangsu Province. A high prevalence of integrons and gene cassettes play an important role in the transmission of drug resistance in S. flexneri. Effective measures are urgently needed to control the spread of multi-drug-resistant S. flexneri, and more continuing active surveillance of antimicrobial resistance should be established worldwide, especially in developing countries.

Patterns of Bacillary Dysentery in China, 2005-2010

Although the incidence of bacillary dysentery in China has been declining progressively, a considerable disease burden still exists. Few studies have analyzed bacillary dysentery across China and knowledge gaps still exist in the aspects of geographic distribution and ecological drivers, seasonality and its association with meteorological factors, urban-rural disparity, prevalence and distribution of Shigella species. Here, we performed nationwide analyses to fill the above gaps. Geographically, we found that incidence increased along an east-west gradient which was inversely related to the economic conditions of China. Two large endemically high-risk regions in western China and their ecological drivers were identified for the first time. We characterized seasonality of bacillary dysentery incidence and assessed its association with meteorological factors, and saw that it exhibits north-south differences in peak duration, relative amplitude and key meteorological factors. Urban and rural incidences among China’s cities were compared, and disparity associated with urbanization level was invariant in most cities. Balanced decrease of urban and rural incidence was observed for all provinces except Hunan. S. flexneri and S. sonnei were identified as major causative species. Increasing prevalence of S. sonnei and geographic distribution of Shigella species were associated with economic status. Findings and inferences from this study draw broader pictures of bacillary dysentery in mainland China and could provide useful information for better interventions and public health planning.

Quantitative proteomic analysis of Shigella flexneri and Shigella sonnei Generalized Modules for Membrane Antigens (GMMA) reveals highly pure preparations

Outer membrane blebs are naturally shed by Gram-negative bacteria and are candidates of interest for vaccines development. Genetic modification of bacteria to induce hyperblebbing greatly increases the yield of blebs, called Generalized Modules for Membrane Antigens (GMMA). The composition of the GMMA from hyperblebbing mutants of Shigella flexneri 2a and Shigella sonnei were quantitatively analyzed using high-sensitivity mass spectrometry with the label-free iBAQ procedure and compared to the composition of the solubilized cells of the GMMA-producing strains. There were 2306 proteins identified, 659 in GMMA and 2239 in bacteria, of which 290 (GMMA) and 1696 (bacteria) were common to both S. flexneri 2a and S. sonnei. Predicted outer membrane and periplasmic proteins constituted 95.7% and 98.7% of the protein mass of S. flexneri 2a and S. sonnei GMMA, respectively. Among the remaining proteins, small quantities of ribosomal proteins collectively accounted for more than half of the predicted cytoplasmic protein impurities in the GMMA. In GMMA, the outer membrane and periplasmic proteins were enriched 13.3-fold (S. flexneri 2a) and 8.3-fold (S. sonnei) compared to their abundance in the parent bacteria. Both periplasmic and outer membrane proteins were enriched similarly, suggesting that GMMA have a similar surface to volume ratio as the surface to periplasmic volume ratio in these mutant bacteria. Results in S. flexneri 2a and S. sonnei showed high reproducibility indicating a robust GMMA-producing process and the low contamination by cytoplasmic proteins support the use of GMMA for vaccines. Data are available via ProteomeXchange with identifier PXD002517.

Emergence of ONPG-negative Shigella sonnei in Shanghai, China

Shigella sonnei has become predominant species causing shigellosis in Shanghai. Two hundred ninety-three S. sonnei were isolated in sentinel hospitals of Shanghai in 2011. We found an emergence of 8 strains of S. sonnei with negative phenotype for o-nitrophenyl-β-d-galactopyranoside in late August, which showed distinct pulsed-field gel electrophoresis patterns from the other 285 S. sonnei and had genes deletion in lac and mhp operons.

Production of a Shigella sonnei Vaccine Based on Generalized Modules for Membrane Antigens (GMMA), 1790GAHB

Recently, we developed a high yield production process for outer membrane particles from genetically modified bacteria, called Generalized Modules of Membrane Antigens (GMMA), and the corresponding simple two step filtration purification, enabling economic manufacture of these particles for use as vaccines. Using a Shigella sonnei strain that was genetically modified to produce penta-acylated lipopolysaccharide (LPS) with reduced endotoxicity and to maintain the virulence plasmid encoding for the immunodominant O antigen component of the LPS, scale up of the process to GMP pilot scale was straightforward and gave high yields of GMMA with required purity and consistent results. GMMA were formulated with Alhydrogel and were highly immunogenic in mice and rabbits. In mice, a single immunization containing 29 ng protein and 1.75 ng of O antigen elicited substantial anti-LPS antibody levels. As GMMA contain LPS and lipoproteins, assessing potential reactogenicity was a key aspect of vaccine development. In an in vitro monocyte activation test, GMMA from the production strain showed a 600-fold lower stimulatory activity than GMMA with unmodified LPS. Two in vivo tests confirmed the low potential for reactogenicity. We established a modified rabbit pyrogenicity test based on the European Pharmacopoeia pyrogens method but using intramuscular administration of the full human dose (100 μg of protein). The vaccine elicited an average temperature rise of 0.5°C within four hours after administration, which was considered acceptable and showed that the test is able to detect a pyrogenic response. Furthermore, a repeat dose toxicology study in rabbits using intramuscular (100 μg/dose), intranasal (80 μg/dose), and intradermal (10 μg/dose) administration routes showed good tolerability of the vaccine by all routes and supported its suitability for use in humans. The S. sonnei GMMA vaccine is now in Phase 1 dose-escalation clinical trials.

Impacts on Human Health Caused by Zoonoses

Zoonosis is an infectious disease and a potential bioterrorism agent. Bioterrorism aimed at a society, government, and/or its citizens is meant to cause destabilization, fear, anxiety, illness, and death in people, animals, or plants using biological agents. A bioterrorism attack is the intentional release of biological agents such as viruses, bacteria, fungi, rickettsial or chlamydial organisms, toxins, or other harmful agents. This chapter focuses on the induction, monitoring, and prevention of some zoonotic diseases that have potential as bioterrorism agents. The etiology, clinical manifestations, transmission routes, and treatment of these zoonotic agents are briefly discussed.

Update on molecular epidemiology of Shigella infection

PURPOSE OF REVIEW

Shigella spp. are important etiologic agents of diarrhea worldwide. This review summarizes the recent findings on the epidemiology, diagnosis, virulence genes, and pathobiology of Shigella infection.

RECENT FINDINGS

Shigella flexneri and Shigella sonnei have been identified as the main serogroups circulating in developing and developed countries, respectively. However, a shift in the dominant species from S. flexneri to S. sonnei has been observed in countries that have experienced recent improvements in socioeconomic conditions. Despite the increasing usage of molecular methods in the diagnosis and virulence characterization of Shigella strains, researchers have been unsuccessful in finding a specific target gene for this bacillus. New research has demonstrated the role of proteins whose expressions are temperature-regulated, as well as genes involved in the processes of adhesion, invasion, dissemination, and inflammation, aiding in the clarification of the complex pathobiology of shigellosis.

SUMMARY

Knowledge about the epidemiologic profile of circulating serogroups of Shigella and an understanding of its pathobiology as well as of the virulence genes is important for the development of preventive measures and interventions to reduce the worldwide spread of shigellosis.

Shift in serotype distribution of Shigella species in China, 2003-2013

We identified 2912 Shigella isolates from diarrhoeal patients in China during 2003-2013. The most common species was Shigella flexneri (55.3%), followed by Shigella sonnei (44.1%); however, S. sonnei is becoming increasingly prevalent. Among the S. flexneri isolates, serotypes 2a and X variant (-:7,8, E1037) were the two most prevalent serotypes, and serologically atypical isolates were also commonly identified. Overall, S. sonnei, S. flexneri 2a and S. flexneri X variant (-:7,8, E1037) accounted for 76.1% of all Shigella isolates, and their prevalence increased from 54.0% during 2003-2004 to 84.1% during 2011-2013. A change was observed in the serotype distribution of Shigella in China during this period, and we propose an ideal strategy to inform the development of a broadly effective Shigella vaccine candidate.

Modulation of endotoxicity of Shigella generalized modules for membrane antigens (GMMA) by genetic lipid A modifications: relative activation of TLR4 and TLR2 pathways in different mutants

Outer membrane particles from Gram-negative bacteria are attractive vaccine candidates as they present surface antigens in their natural context. We previously developed a high yield production process for genetically derived particles, called generalized modules for membrane antigens (GMMA), from Shigella. As GMMA are derived from the outer membrane, they contain immunostimulatory components, especially lipopolysaccharide (LPS). We examined ways of reducing their reactogenicity by modifying lipid A, the endotoxic part of LPS, through deletion of late acyltransferase genes, msbB or htrB, in GMMA-producing Shigella sonnei and Shigella flexneri strains. GMMA with resulting penta-acylated lipid A from the msbB mutants showed a 600-fold reduced ability, and GMMA from the S. sonnei ΔhtrB mutant showed a 60,000-fold reduced ability compared with GMMA with wild-type lipid A to stimulate human Toll-like receptor 4 (TLR4) in a reporter cell line. In human peripheral blood mononuclear cells, GMMA with penta-acylated lipid A showed a marked reduction in induction of inflammatory cytokines (S. sonnei ΔhtrB, 800-fold; ΔmsbB mutants, 300-fold). We found that the residual activity of these GMMA is largely due to non-lipid A-related TLR2 activation. In contrast, in the S. flexneri ΔhtrB mutant, a compensatory lipid A palmitoleoylation resulted in GMMA with hexa-acylated lipid A with ∼10-fold higher activity to stimulate peripheral blood mononuclear cells than GMMA with penta-acylated lipid A, mostly due to retained TLR4 activity. Thus, for use as vaccines, GMMA will likely require lipid A penta-acylation. The results identify the relative contributions of TLR4 and TLR2 activation by GMMA, which need to be taken into consideration for GMMA vaccine development.

Epidemic and virulence characteristic of Shigella spp. with extended-spectrum cephalosporin resistance in Xiaoshan District, Hangzhou, China

BACKGROUND

Shigellae have become increasingly resistant to the extended-spectrum cephalosporin (ESC) worldwide and pose a great challenge to anti-infection treatment options. The purpose of this study was to determine the resistance, cephalosporin resistance mechanisms, virulence characteristic and genotype of ESC-resistant Shigella.

METHODS

From 2008 to 2012, Shigella isolates collected from diarrhea patients were detected for antibiotics sensitivity by disk diffusion, cephalosporin resistance determinants and virulence genes using polymerase chain reaction (PCR) and genotyping through enterobacterial repetitive intergenic consensus sequence PCR (ERIC-PCR).

RESULTS

A total of 356 Shigella isolates were gathered, and 198 (55.6%, 58 S. flexneri and 140 S. sonnei) were resistant to ESC. All ESC-resistant isolates were susceptible to imipenem, and only 0.5% isolate was resistant to piperacillin/tazobactam. ESC-resistant S. flexneri showed high degrees of resistance to ampicillin (100%), ampicillin/sulbactam (96.6%), piperacillin (100%), trimethoprim/sulfamethoxazole (74.1%), ciprofloxacin (74.1%), levofloxacin (53.4%), ceftazidime (58.6%) and cefepime (58.6%). ESC-resistant S. sonnei exhibited high resistance rates to ampicillin (100%), piperacillin (100%) and trimethoprim/sulfamethoxazole (96.4%). Cephalosporin resistance genes were confirmed in 184 ESC-resistant isolates. bla(CTX-M) types (91.8%, mainly bla(CTX-M-14), bla(CTX-M-15) and bla(CTX-M-57)) were most prevalent, followed by bla(OXA-30) (26.3%). Over 99.0% ESC-resistant isolates harbored virulence genes ial, ipaH, virA and sen. However, set1 were more prevalent in ESC-resistant S. flexneri isolates than in S. sonnei isolates. ERIC-PCR results showed that 2 and 3 main genotypes were detected in ESC-resistant S. flexneri and S. sonnei, respectively.

CONCLUSION

Our findings indicated that a high prevalence of ESC-resistant Shigella mediated mainly by bla(CTX-M) with stronger resistance and virulence, and the existence of specific clones responsible for these Shigella infection in the region studied.

Shigella: A Highly Virulent and Elusive Pathogen

Despite a significant decrease in Shigella-related mortality, shigellosis continues to carry a significant burden of disease worldwide, particularly in Asia and Africa. Shigella is a highly virulent pathogen comprised of four major species with numerous subtypes. Shigella dysenteriae and Shigella flexneri infections are predominant in resource-limited settings. Clinical presentations range from mild watery diarrhea to severe dysentery with systemic complications such as electrolyte imbalance, seizures and hemolytic uremic syndrome. S. dysenteriae subtype 1, the producer of Shiga toxin, causes the most severe illness and highest mortality. Susceptible strains of Shigella may be effectively treated with inexpensive oral antibiotics such as ampicillin or trimethoprim-sulfamethoxazole. Unfortunately, multidrug resistant strains have emerged that have rendered most antibiotics, including fluoroquinolones and extended-spectrum cephalosporins, ineffective. Management and prevention of shigellosis represents a major public health challenge. The development of an effective vaccine is urgently needed to decrease its global impact.

Linear synthesis of the branched pentasaccharide repeats of O-antigens from Shigella flexneri 1a and 1b demonstrating the major steric hindrance associated with type-specific glucosylation

Shigella flexneri serotypes 1b and 1a are Gram-negative enteroinvasive bacteria causing shigellosis in humans.