A pentaplex PCR assay for the detection and differentiation of Shigella species

"Molecular Characterization of Extended Spectrum Beta-Lactamase Resistance in Pediatric Shigella Isolates in Egypt"

Shigellosis is a major cause of morbidity and mortality among children, especially in developing countries. The increased extended-spectrum beta-lactamase (ESBL) resistance in Shigella poses a challenge for effective treatment. To examine the antibiotic resistance and ESBL profile of Shigella isolates from children with acute diarrhea. Shigella was isolated from stool cultures from pediatric patients suffering from acute diarrhea. The isolates were identified by bacteriological tests, serotyping, and multiplex polymerase chain reaction (PCR). The antimicrobial resistance was examined by disc diffusion. Phenotypic tests and PCR examined the ESBLs and CTX-M, SHV, and TEM genes. A total of 100 Shigella (10% prevalence rate) were isolated. The S. sonnei and S. dysenteries were the most prevalent species (33% and 31%, respectively), followed by S. flexneri (27%), and only 9% were S. boydii. The isolates had complete resistance (100%) to ampicillin. There was lower resistance to ciprofloxacin (24%), and no resistance to imipenem. By phenotypic tests, 54% of isolates had ESBL. By PCR, bla-CTX-M gene was the most prevalent (50%), followed by bla-TEM (48.1%). Only one isolate (1.9%) had the bla-SHV gene. The alarmingly high rates of antibiotic resistance and ESBL resistance among Shigella spp highlight the urgent need to restrict the unguided use of these drugs. Continuous monitoring of local and global antibiotic resistance patterns is required to prevent the spread of resistance.

Investigation of the vaccine potential of an in silico designed FepA peptide vaccine against Shigella flexneri in mice model

Background

Shigellosis is one of the significant causes of diarrhea in Bangladesh. It is a global health problem; approximately 1.3 million people die yearly from Shigellosis. The current treatment method, using different antibiotics against Shigellosis is ineffective. Moreover, it becomes a worrying situation due to the emergence of antibiotic-resistant pathogenic microbes responsible for these diarrheal diseases.

Methodology

Previous immunoinformatics study predicted a potential peptide from the Ferric enterobactin protein (FepA) of Shigella spp. In this study, we have chemically synthesized the FepA peptide. As a highly immunogenic, FepA peptide conjugated with KLH has been tested in mice model with complete and incomplete adjuvants as a vaccine candidate.

Results

Immunological analysis showed that all vaccinated mice were immunologically boosted, which was statistically significant (P-value 0.0325) compared to control mice. Immunological analysis for bacterial neutralization test result was also statistically significant (P-value 0.0468), where each ELISA plate was coated with 1 × 107S. flexneri cells. The Challenge test with 1 × 1012S. flexneri cells to each vaccinated and controlled mice showed that 37.5 % of control (non-vaccinated) mice died within seven days after the challenge was given while 100 % of vaccinated mice remained strong and stout. The analyses of the post-challenge weight loss of the mice were also significant (P-value 0.0367) as the weight loss percentage in control mice was much higher than in the vaccinated mice. The pathological and phenotypic appearances of vaccinated mice were also clearly differentiable compared with control mice. Thus all these immunological analysis and pathological appearances directly supported our FepA peptide as a potential immune booster.

Conclusion

This study provides evidence that the FepA peptide is a highly immunogenic vaccine candidate against S. flexneri. Therefore, these findings inspire future trials for the evaluation of the suitability of this vaccine candidate against Shigellosis.

Characterization of genotypes and antimicrobial resistance profiles of clinical isolates of Shigella from patients in the southern region of Iran

BACKGROUND

Shigella spp., which are facultative anaerobic bacilli within the Enterobacteriaceae family, present a significant public health burden due to their role as prominent contributors to diarrheal diseases worldwide. A molecular analysis can facilitate the identification and assessment of outbreaks involving this bacterium. So, we aimed to investigate the antibiotic susceptibility pattern and clonal relatedness of clinical Shigella spp. isolates obtained from patients with diarrhea in Hormozgan province, South of Iran.

METHODS

From 2019 to 2021, a cross-sectional investigation was conducted on 448 stool samples obtained from patients who were experiencing diarrhea, in the southern region of Iran. Shigella spp. isolates were identified based on biochemical and serological tests. All Shigella species were verified using species-specific polymerase chain reaction (PCR), followed by susceptibility testing to antimicrobial agents. Subsequently, genotyping of all Shigella species was conducted using ERIC-PCR.

RESULTS

Out of a total of 448 stool samples, the presence of Shigella was detected in 62 cases, accounting for a prevalence rate of 13.84%. Among the identified isolates, the majority were attributed to S. flexneri, representing 53.23% of the cases. This was followed by S. sonnei at 24.19% and S. boydii at 22.58%. Notably, no instances of S. dysenteriae were found. The highest prevalence of Shigella isolates was observed in infants and children under the age of five. A significant proportion of the identified isolates demonstrated resistance to various antibiotics. Specifically, high resistance rates were noted for ampicillin (90.78%), piperacillin-tazobactam (87.1%), cefixime (83.87%), trimethoprim-sulfamethoxazole (83.87%), cefotaxime (82.26%), and ceftriaxone (80.65%). In addition, a substantial number (87.1%) of the isolates exhibited a multidrug-resistant (MDR) phenotype. Using the ERIC-PCR method, a total of 11 clusters and 6 distinct single types were identified among all the Shigella isolates.

CONCLUSION

A notable occurrence of antibiotic-resistant Shigella species has been noted, with multi-drug resistant (MDR) strains presenting an increasing challenge for treating shigellosis worldwide, and this includes Iran. Techniques such as ERIC-PCR are useful for assessing the genetic variation and connections between Shigella strains, which indirectly contributes to understanding antimicrobial resistance patterns. Further research is needed to explore the specific correlation between resistance genes and ERIC genotyping patterns in Shigella strains.

Development of a recombinase polymerase amplification assay with lateral flow dipstick (RPA-LFD) for rapid detection of Shigella spp. and enteroinvasive Escherichia coli

Shigella spp. and enteroinvasive Escherichia coli (EIEC) are widely distributed and can cause serious food-borne diseases for humans such as dysentery. Therefore, an efficient detection platform is needed to detect Shigella and EIEC quickly and sensitively. In this study, a method called recombinase polymerase amplification combined with lateral flow dipstick (RPA-LFD) was developed for rapid detection of Shigella and EIEC. RPA primers and LFD detection probes were designed for their shared virulence gene ipaH. Primers and probes were screened, and the primer concentration, and reaction time and temperature were optimized. According to the optimization results, the RPA reaction should be performed at 39°C, and when combined with LFD, it takes less than 25 min for detection with the naked eye. The developed RPA-LFD method specifically targets gene ipaH and has no cross-reactivity with other common food-borne pathogens. In addition, the minimum detection limit of RPA-LFD is 1.29×102 copies/μL. The detection of food sample showed that the RPA-LFD method was also verified for the detection of actual samples.

Molecular detection and characterization of Shigella spp. harboring extended-spectrum β-lactamase genes in children with diarrhea in northwest Iran

Shigellosis is one of the acute bowel infections and remains a serious public health problem in resource-poor countries. The present study aimed to survey the distribution of extended-spectrum β-lactamase (ESBL)-producing Shigella strains isolated from patients with diarrhea in northwest Iran. In the present cross-sectional study, from January 2019 to December 2020, 1280 fecal samples were collected from children with diarrhea in Ardabil, Iran. Multiplex PCR assay was applied for the presence of ipaH, invC, wbgZ, rfpB, and rfc genes to detect Shigella spp., Shigella sonnei, Shigella dysenteriae, Shigella flexneri, and Shigella boydii, respectively. Phenotypic detection of ESBL-producing isolates was carried out using the Double Disc Test (DDT). The frequency of main ESBL encoding genes including bla_CTX-M, bla_SHV, and bla_TEM was detected using multiplex PCR. The genetic similarity of S. sonnei isolates was determined using ERIC PCR. A total of 49 Shigella isolates (3.8%; 49/1280) including 42 (85.7%) S. sonnei, 5 (10.2%) S. flexneri, and 2 (4%) S. dysenteriae were identified. S. boydii was not detected in any fecal samples. ESBLs were produced by 10.2% of Shigella spp. including 3 S. sonnei, 1 S. flexneri, and 1 S. dysenteriae. The ESBL encoding genes include bla_CTX-M and bla_TEM found in 65.3% and 61.2% of isolates, respectively. bla_SHV gene was not detected in any isolates. The ERIC-PCR profiles allowed the differentiation of 42 S. sonnei strains into 6 clusters. Our study revealed a high frequency of ESBL-encoding genes among Shigella spp. in northwest Iran. The high prevalence of S. sonnei harboring ESBL genes, in the present work, is the main challenge for dysentery treatment, and this concern justifies the need for effective and regular monitoring of antibiotic usage among patients.

The Detection of Foodborne Pathogenic Bacteria in Seafood Using a Multiplex Polymerase Chain Reaction System

Multiplex polymerase chain reaction (PCR) assays are mainly used to simultaneously detect or identify multiple pathogenic microorganisms. To achieve high specificity for detecting foodborne pathogenic bacteria, specific primers need to be designed for the target strains. In this study, we designed and achieved a multiplex PCR system for detecting eight foodborne pathogenic bacteria using specific genes: toxS for Vibrio parahaemolyticus, virR for Listeria monocytogenes, recN for Cronobacter sakazakii, ipaH for Shigella flexneri, CarA for Pseudomonas putida, rfbE for Escherichia coli, vvhA for Vibrio vulnificus, and gyrB for Vibrio alginolyticus. The sensitivity of the single system in this study was found to be 20, 1.5, 15, 15, 13, 14, 17, and 1.8 pg for V. parahaemolyticus, L. monocytogenes, E. coli O157:H7, C. sakazakii, S. flexneri, P. putida, V. vulnificus, and V. alginolyticus, respectively. The minimum detection limit of the multiplex system reaches pg/μL detection level; in addition, the multiplex system exhibited good specificity and stability. Finally, the assays maintained good specificity and sensitivity of 10⁴ CFU/mL for most of the samples and we used 176 samples of eight aquatic foods, which were artificially contaminated to simulate the detection of real samples. In conclusion, the multiplex PCR method is stable, specific, sensitive, and time-efficient. Moreover, the method is well suited for contamination detection in these eight aquatic foods and can rapidly detect pathogenic microorganisms.

Development of multiplex cross displacement amplification combined with lateral flow biosensor assay for detection of virulent shigella sonnei

Shigella sonnei is the most common Shigella spp. in developed areas and the second most common in undeveloped regions. In this study, a multiple cross displacement amplification (MCDA) assay was used in combination with a lateral flow biosensor (LFB) assay to detect virulent S. sonnei strains containing the ipaH and wbgX genes. The multiplex MCDA-LFB assay detected wbgX at ≥1 pg/μL and ipaH at ≥10 fg/μL within 30 min in pure cultures maintained at 63°C. This assay was sensitive for ~37 CFU of virulent S. sonnei and ~3.7 CFU of Shigella spp. and enteroinvasive E. coli in stimulated fecal samples and had 100% specificity among 59 reference strains. The MCDA-LFB assay was also able to differentiate between virulent S. sonnei and other Shigella spp. and enteroinvasive E. coli among 99 clinical isolates. In summary, a multiplex MCDA-LFB assay was developed for rapid, convenient, point-of-care, and accurate identification of virulent S. sonnei within 30 min and at a constant temperature without the need for expensive lab equipment.

Efficient classification of Escherichia coli and Shigella using FT-IR spectroscopy and multivariate analysis

Accurate and effective discrimination of E. coli and Shigella is an important clinical issue, and there are many limitations in traditional methods of analysis. FT-IR shows great potential in the classification of bacteria with high specificity and low cost. In this study, we evaluated the efficiency of this technique when combined with multivariate analysis for rapid classification of E. coli and Shigella, which is difficult using traditional analytical methods. Machine learning and statistical tools were employed in combination with FT-IR to classify 14 E. coli and 9 Shigella strains. The classification accuracies for select E. coli and Shigella strains from blood agar were 0.7826, 0.8696, and 0.9565 at the genus, species, and strain levels, respectively. In addition, we used the FT-IR data of select strains from three different culture media for cross-validation, yielding an accuracy of 0.3681 at the strain level. These results indicate that the bacterial culture conditions have a significant impact on the FT-IR patterns. Based on this, an improved strategy for training an ensemble classifier model considering bacterial culture factors was constructed, resulting in almost perfect separation with an accuracy of 0.9394 for strain-level classification. These results show the potential of FT-IR combined with multivariate analysis for more reliable bacterial classification.

Development and Application of a Multiplex Fluorescent PCR for Shigella Detection and Species Identification

This study was to develop a multiplex fluorescent PCR for Shigella detection and species identification. Five primer pairs for Shigella detection and species identification were designed by Primer Premier 5.0. The multiplex fluorescent PCR was optimized by varying single parameter while other parameters were maintained. The multiplex fluorescent PCR assay could correctly detect Shigella and identify four Shigella species with a detection limits of 10 pg genomic DNA per reaction. Testing different strains and clinical samples confirmed the sensitivity and specificity of the multiplex fluorescent PCR. The newly developed multiplex fluorescent PCR assay is simple, sensitive and specific for Shigella detection and species identification. It has a potential to be used in routine Shigella detection and species identification in clinical laboratories.

Development of high-resolution melting (HRM) assay to differentiate the species of Shigella isolates from stool and food samples

Shigella species, a group of intracellular foodborne pathogens, are the main causes of bacillary dysentery and shigellosis in humans worldwide. It is essential to determine the species of Shigella in outbreaks and food safety surveillance systems. The available immunological and molecular methods for identifying Shigella species are relatively complicated, expensive and time-consuming. High resolution melting (HRM) assay is a rapid, cost-effective, and easy to perform PCR-based method that has recently been used for the differentiation of bacterial species. In this study, we designed and developed a PCR-HRM assay targeting rrsA gene to distinguish four species of 49 Shigella isolates from clinical and food samples and evaluated the sensitivity and specificity of the assay. The assay demonstrated a good analytical sensitivity with 0.01–0.1 ng of input DNA template and an analytical specificity of 100% to differentiate the Shigella species. The PCR-HRM assay also was able to identify the species of all 49 Shigella isolates from clinical and food samples correctly. Consequently, this rapid and user-friendly method demonstrated good sensitivity and specificity to differentiate species of the Shigella isolates from naturally contaminated samples and has the potential to be implemented in public health and food safety surveillance systems.

Historical, current, and emerging tools for identification and serotyping of Shigella

The Shigella genus includes serious foodborne disease etiologic agents, with 4 species and 54 serotypes. Identification at species and serotype levels is a crucial task in microbiological laboratories. Nevertheless, the genetic similarity between Shigella spp. and Escherichia coli challenges the correct identification and serotyping of Shigella spp., with subsequent negative repercussions on surveillance, epidemiological investigations, and selection of appropriate treatments. For this purpose, multiple techniques have been developed historically ranging from phenotype-based methods and single or multilocus molecular techniques to whole-genome sequencing (WGS). To facilitate the selection of the most relevant method, we herein provide a global overview of historical and emerging identification and serotyping techniques with a particular focus on the WGS-based approaches. This review highlights the excellent discriminatory power of WGS to more accurately elucidate the epidemiology of Shigella spp., disclose novel promising genomic targets for surveillance methods, and validate previous well-established methods.

DNA sequencing, genomes and genetic markers of microbes on fruits and vegetables

The development of DNA sequencing technology has provided an effective method for studying foodborne and phytopathogenic microorganisms on fruits and vegetables (F & V). DNA sequencing has successfully proceeded through three generations, including the tens of operating platforms. These advances have significantly promoted microbial whole‐genome sequencing (WGS) and DNA polymorphism research. Based on genomic and regional polymorphisms, genetic markers have been widely obtained. These molecular markers are used as targets for PCR or chip analyses to detect microbes at the genetic level. Furthermore, metagenomic analyses conducted by sequencing the hypervariable regions of ribosomal DNA (rDNA) have revealed comprehensive microbial communities in various studies on F & V. This review highlights the basic principles of three generations of DNA sequencing, and summarizes the WGS studies of and available DNA markers for major bacterial foodborne pathogens and phytopathogenic fungi found on F & V. In addition, rDNA sequencing‐based bacterial and fungal metagenomics are summarized under three topics. These findings deepen the understanding of DNA sequencing and its application in studies of foodborne and phytopathogenic microbes and shed light on strategies for the monitoring of F & V microbes and quality control.

Molecular characterization of quinolone resistant Shigella spp. isolates from patients in Ardabil, Iran

BACKGROUND AND OBJECTIVES

Shigella is an etiological agent of shigellosis. Antibiotic therapy has a critical role in decreasing serious complications of shigellosis. The present study aimed to determine the multi-drug resistance strains and to detect fluoroquinolone related mutations.

MATERIALS AND METHODS

In this descriptive, cross sectional study, a total of 113 Shigella isolates were collected from 1280 patients admitted to Bu-Ali hospital in Ardabil province during 2015-17. Antibiotic resistance pattern of isolates was evaluated using Kirby Bauer method and finally, the MICs of ciprofloxacin were determined. In order to determine any mutations in QRDR region, parC and gyrA genes of resistant strains were amplified and sequenced.

RESULTS

Shigella spp. isolates were identified using ipaH amplification and rfc and wbgz genes were used for molecular detection of S. flexneri and S. soneii, respectively. Our results showed that the predominant species in Ardabil province was S. sonnei (69.91%). Most of isolates (82%) were resistant to trimethoprim/sulfamethoxazole (TMP/SMX); 51% were nalidixic acid resistant and 4.4% were floroquinolones resistant. All examined isolates were susceptible to imipenem (100%). Mutation in gyrA and parC genes were detected in all fluoroquinolone resistant isolates (5 isolates). Although, in this study the rate of resistance to ciprofloxacin was low, but in the lack of preventive strategy it will be a major challenge of public health in future.

CONCLUSION

This study provided information on the prevalence and antimicrobial susceptibility patterns of Shigella isolates in Ardabil province, Iran. Also this study showed a high-level of resistance to commonly used antibiotics among Shigella isolates.

Utilization of Small RNA Genes to Distinguish Vibrio cholerae Biotypes via Multiplex Polymerase Chain Reaction

The diarrheal disease "cholera" is caused by Vibrio cholerae, and is primarily confined to endemic regions, mostly in Africa and Asia. It is punctuated by outbreaks and creates severe challenges to public health. The disease-causing strains are most-often members of serogroups O1 and O139. PCR-based methods allow rapid diagnosis of these pathogens, including the identification of their biotypes. However, this necessitates the selection of specific target sequences to differentiate even the closely related biotypes of V. cholerae. Oligonucleotides for selective amplification of small RNA (sRNA) genes that are specific to these V. cholerae subtypes were designed. The resulting multiplex PCR assay was validated using V. cholerae cultures (i.e., 19 V. cholerae and 22 non-V. cholerae isolates) and spiked stool samples. The validation using V. cholerae cultures and spiked stool suspensions revealed detection limits of 10-100 pg DNA per reaction and 1.5 cells/mL suspension, respectively. The multiplex PCR assay that targets sRNA genes for amplification enables the sensitive and specific detection, as well as the differentiation of V. cholerae-O1 classical, O1 El Tor, and O139 biotypes. Most importantly, the assay enables fast and cheaper diagnosis compared with classic culture-based methods.

Precise, direct, and rapid detection of Shigella Spa gene by a novel unmodified AuNPs-based optical genosensing system

Early detection of infectious bacteria is a necessity for combating infectious diseases. Due to low infectious dose of Shigella, rapid and sensitive detection is needed. Compared to the presented genes, Spa gene can be introduced as a novel sequence for all species of Shigella detection. Herein, the possibility of Spa genes for detection of four species of Shigella was investigated for the first time by AuNPs-based optical genosensing system. In this method, AuNP-DNA probes were hybridized with Spa gene sequence. When the complementary target is present, it prevents the aggregation of the complex under acid environment and the solution remains red whereas in the absence of the specific sequence, it turns to purple. Therefore, visual detection is possible with bare eye. The comparison of this Optical DNA biosensor and PCR-based method showed that the proposed method is simple, cost-effective, rapid operation, with high or comparable detection limit of (LOD and LOQ: 8.14 and 26.6 ng mLl^-1, respectively), without need of any expensive techniques, and equipments compared to the conventional methods. In conclusion, the described method may develop into a platform that could be utilized for detection of various bacterial species with high accuracy and prompt screening of samples.

First investigation of the presence of SPATE genes in Shigella species isolated from children with diarrhea infection in Ahvaz, southwest Iran

Background:SPATE (serine protease autotransporters of enterobacteriaceae) genes are considered as a group of the main virulence factors of Shigella species This study aimed to investigate for the first time the distribution of SPATE genes among Shigella spp. isolated from children with diarrhea infection in Ahvaz, Iran.

Methodology: In this study, a total of 74 Shigella isolates were collected between August 2016 and June 2017 from feces of children with diarrhea and identified by biochemical and molecular methods for Shigella species. The frequency distribution of the SPATE genes, including pic, pet, sat, sigA and sepA, was evaluated using PCR. The genetic relationship of all isolates was evaluated by enterobacterial repetitive intergenic consensus-PCR.

Results: The most common species of Shigella was S. flexneri, followed by S. sonnei and S. boydii. In total, 95.94% of Shigella isolates had at least one of the SPATE genes. The presence of pic, pet, sat, sigA and sepA genes was confirmed among 35.13%, 27%, 47.29%, 58.1% and 39.18% of Shigella isolates, respectively. Of these SPATE genes, the sat and sigA genes were recognized as the most common autotransporters among S. flexneri and S. sonnei isolates, respectively. Also, either S. flexneri or S. sonnei isolates belonging to a same clone type had similar SPATE genes profile.

Conclusion: Our results revealed that the high distribution of SPATE genes among Shigella isolates in our region. Hence, this study highlights a need for epidemiological programs to monitor the distribution of SPATE genes locally for prevention from further dissemination of the Shigella isolates harboring them.

Shifting national surveillance of Shigella infections toward geno-serotyping by the development of a tailored Luminex assay and NGS workflow

The phylogenetically closely related Shigella species and enteroinvasive Escherichia coli (EIEC) are responsible for millions of episodes of bacterial dysenteriae worldwide. Given its distinct epidemiology and public health relevance, only Shigellae are subject to mandatory reporting and follow‐up by public health authorities. However, many clinical laboratories struggle to differentiate non‐EIEC, EIEC, and Shigella in their current workflows, leading to inaccuracies in surveillance and rising numbers of misidentified E. coli samples at the National Reference Centre (NRC). In this paper, we describe two novel tools to enhance Shigella surveillance. First, we developed a low‐cost Luminex‐based multiplex assay combining five genetic markers for species identification with 11 markers for serotype prediction for S. sonnei and S. flexneri isolates. Using a test panel of 254 clinical samples, this assay has a sensitivity of 100% in differentiation of EIEC/Shigella pathotype from non‐EIEC strains, and 68.7% success rate in distinction of Shigella and EIEC. A novel, and particularly successful marker was a Shigella‐specific deletion in the spermidine acetyltransferase gene speG, reflecting its metabolic decay. For Shigella serotype prediction, the multiplex assay scored a sensitivity and specificity of 96.6% and 98.4%, respectively. All discrepancies were analyzed with whole‐genome sequencing and shown to be related to causative mutations (stop codons, indels, and promoter mutations) in glycosyltransferase genes. This observation spurred the development of an in silico workflow which extracts the Shigella serotype from Next‐Generation Sequencing (NGS) data, taking into account gene functionality. Both tools will be implemented in the workflow of the NRC, and will play a major role in the shift from phenotypic to genotyping‐based surveillance of shigellosis in Belgium.

Prevalence of enterotoxin-encoding genes among diverse Shigella strains isolated from patients with diarrhea, southwest Iran

Shigella spp. are a major cause of bacillary dysentery, particularly among children in developing countries such as Iran. This study aimed to investigate the presence of two important Shigella enterotoxins (ShET-1 and ShET-2), encoded by the set and sen genes, respectively, by polymerase chain reaction (PCR) assay among Shigella species isolated from children affected by shigellosis in Ahvaz, southwest of Iran. In this cross-sectional study, from June 2016 to April 2017, altogether 117 Shigella isolates were collected from fecal specimens of children aged <15 years with diarrhea in Ahvaz, southwest Iran. All isolates were identified by standard microbiological and molecular methods. The presence of enterotoxin genes was determined by PCR. The most prevalent isolate was Shigella flexneri (47.9%), followed by Shigella sonnei (41%) and Shigella boydii (11.1%), respectively. Shigella dysenteriae was not detected in patients' samples. The frequencies of set1A, set1B, and sen genes were 5.1% (6/117), 15.4% (18/117), and 76.9% (90/117), respectively. This study provides initial background on the prevalence and distribution of the Shigella enterotoxin genes in Shigella isolates in southwest of Iran. In addition, this study revealed a high prevalence of sen enterotoxin gene in Shigella species.

An impedimetric aptasensor for Shigella dysenteriae using a gold nanoparticle-modified glassy carbon electrode

This work describes an aptasensor for the foodborne pathogen Shigella dysenteriae (S. dysenteriae). A glassy carbon electrode (GCE) was modified with gold nanoparticles (AuNPs) by electrodeposition. Then, thiolated aptamer for S. dysenteriae detection was self-assembled on the surface of the modified GCE, and any free residual AuNPs were blocked with 6-mercapto-1-hexanol. The size, morphology, and distribution of the AuNPs were characterized by field emission scanning electron microscopy. Detection of S. dysenteriae was performed measurement of the charge transfer resistance (R_ct) before and after addition of S. dysenteriae using hexacyanoferrate as an electrochemical probe. The interaction between the aptamer and outer-membrane proteins of S. dysenteriae lead to an increase in the R_ct of the sensor. The assay has a linear dynamic range that extends from 10¹ to 10⁶ CFU.mL^-1 and a limit of detection of 10⁰ CFU.mL^-1. It can differentiate between alive S. dysenteriae and other pathogens. Dead S. dysenteriae cells do not have any effect on selectivity. Unpasteurized and pasteurized skim milk and some water samples were spiked with S. dysenteriae and then successfully examined by this method. The results were validated by real-time PCR. The method is fast, low-cost, highly sensitive, and specific. Hence, it represents a valuable tool in food quality control. Graphical abstract Schematic presentation of a label free impedimetric aptasensor for Shigella dysenteriae using a glassy carbon electrode modified with gold nanoparticles (AuNPs) and 6-mercapto-1-hexanol (MCH). The limit of detection of this aptasensor is as low as 1 CFU.mL^-1 for target bacteria.

Enterobacterial repetitive intergenic consensus (ERIC)-PCR analysis as a reliable evidence for suspected Shigella spp. outbreaks

BACKGROUND

Shigellosis remains a serious public health problem and an important cause of morbidity and mortality worldwide. The aim of this study was to characterize fliC and the genetic relatedness of Shigella spp. isolated during a one-year period from children in a suspected outbreak in Tehran, Iran.

METHODS AND RESULTS

Fifty Shigella spp. were isolated from 3779 stool samples of children with diarrhea (prevalence rate: 1.32%). Among the isolates, 92% were characterized as Shigella sonnei, while 6% and 2% were identified as S. flexneri and S. boydii, respectively. S. dysenteriae was not recovered from the patients. All isolates were negative for fliC except for Shigella standard strains. The enterobacterial repetitive intergenic consensus-polymerase chain reaction (ERIC-PCR) profiles allowed differentiating the 50 isolates into 5 ERIC types, which were grouped into five clusters (ET1-ET5). Computer-assisted clustering of the strains showed a high degree of similarity among the isolates.

CONCLUSION

In conclusion, given the clonal correlation of the Shigella strains isolated in this study and the lack of fliC among them, we propose that probably a single or limited fliC-defected Shigella clone spread and caused the outbreak.

Outer membrane proteins analysis of Shigella sonnei and evaluation of their antigenicity in Shigella infected individuals

Bacillary dysentery caused by infection with Shigella spp. remains as serious and common health problem throughout the world. It is a highly multi drug resistant organism and rarely identified from the patient at the early stage of infection. S. sonnei is the most frequently isolated species causing shigellosis in industrialized countries. The antigenicity of outer membrane protein of this pathogen expressed during human infection has not been identified to date. We have studied the antigenic outer membrane proteins expressed by S. sonnei, with the aim of identifying presence of specific IgA and IgG in human serum against the candidate protein biomarkers. Three antigenic OMPs sized 33.3, 43.8 and 100.3 kDa were uniquely recognized by IgA and IgG from patients with S. sonnei infection, and did not cross-react with sera from patients with other types of infection. The antigenic proteome data generated in this study are a first for OMPs of S. sonnei, and they provide important insights of human immune responses. Furthermore, numerous prime candidate proteins were identified which will aid the development of new diagnostic tools for the detection of S. sonnei.

Prevalence of Multidrug-Resistant Bacteria from U.S.-Grown and Imported Fresh Produce Retailed in Chain Supermarkets and Ethnic Stores of Davidson County, Tennessee

The aim of this study was to determine whether U.S.-grown and imported fresh produce retailed in ethnic stores and chain supermarkets was a reservoir of antibiotic-resistant bacteria. A total of 360 (129 imported and 231 U.S.-grown) samples of fresh produce were purchased from retail stores and analyzed for Enterobacteriaceae , including three pathogenic bacteria ( Escherichia coli O157:H7, Shigella , and Salmonella ), using standard methods. Presumptive pathogenic isolates were confirmed using PCR. The mean Enterobacteriaceae counts for imported produce were 6.87 ± 0.15 log CFU/g and 7.16 ± 0.11 log CFU/g in ethnic stores and chain supermarkets, respectively. For U.S.-grown produce, the contamination levels were at 8.35 ± 0.17 log CFU/g and 7.52 ± 0.13 log CFU/g in ethnic stores and chain supermarkets, respectively. Salmonella (0 and 0.3%), Shigella (1.7 and 0.6%), E. coli (3.1 and 1.4%), Enterobacter (9.4 and 8.6%), Klebsiella (6.7 and 0.6%), and Serratia (5.8 and 1.4%) were detected in produce from ethnic stores and chain supermarkets, respectively. None of the samples were positive for E. coli O157:H7. Regarding distribution by produce type, leafy vegetables had a significantly (P < 0.05) higher prevalence of Enterobacteriaceae (19.2%) than the other types, followed by root vegetables (6.4%), tomatoes (5.6%), and fruits (3.9%). Antibiotic-resistant Salmonella , Shigella , E. coli , Enterobacter , Klebsiella , and Erwinia bacteria were also isolated from fresh produce. The frequencies of vancomycin resistance (98.1 and 100%) were significantly higher (P < 0.05) than the frequencies of ampicillin resistance (42.3 and 72.9%) for imported and U.S.-grown produce, respectively. Despite the increased attention to the role of imported produce as a source of antimicrobial resistance, this study indicates that U.S.-grown produce is also contaminated with antibiotic-resistant bacteria. Good agricultural practices on the farms and washing of fresh produce before consumption are greatly recommended to avoid possible public health hazards.

Investigation of Efflux-Mediated Tetracycline Resistance in Shigella Isolates Using the Inhibitor and Real Time Polymerase Chain Reaction Method

BACKGROUND

Shigella spp. are gram negative bacteria, which are of global public health importance. The growing of multidrug-resistant Shigella isolates are a major problem around the world.

METHODS

Overall, 50 isolates of Shigella spp. from children diarrheic stools were studied. The isolates were identified and confirmed using biochemical, serological and molecular methods (ipaH, wbgZ and rfc genes). Antimicrobial susceptibility test was done according to the Clinical and Laboratory Standards Institute (CLSI) guidelines against minocycline, tetracycline, doxycycline, ampicillin, streptomycin, trimethoprim-sulfamethoxazole, nalidixic acid, norfloxacin, ciprofloxacin and levofloxacin. Also, the role of efflux pump in defense of Shigella against tetracycline was investigated by Minimum Inhibitory Concentration (MIC) with and without an efflux pump inhibitor. Detection of tetA, tetB, tetC and tetD genes in Shigella was evaluated by conventional Polymerase Chain Reaction (PCR) and real time PCR.

RESULTS

Molecular identification revealed a prevalence of 14% for Shigella flexneri and 86% for Shigella sonnei. Minimum Inhibitory Concentration (MIC) of 90% of resistant isolates was changed in the presence CCCP. Results of conventional PCR exhibited that 66% of isolates were positive for tetA, while according to real time PCR method, 90% of isolates carried tetA. Positive results for tetB were 12% and 18% by conventional and real time PCR methods, respectively. No positive results were detected for tetC and tetD. Also, tetB was detected only in S. flexneri while tetA was detected in both S. flexneri and S. sonnei.

CONCLUSION

It seems that efflux-mediated tetracycline resistance to tetracycline in S. flexneri can be related to tetB, however resistance in S. sonnei can be related to the expression of tetA.

Multiple- locus variable-number tandem-repeat analysis (MLVA) of Shigella sonnei isolates of 2012 outbreak I. R. Iran

Shigella sonnei is a major cause of diarrhea especially in children. Molecular study can help to determine the outbreak of this bacterium. Multiple-Locus Variable number tandem repeat Analysis (MLVA) will largely influence the public health field by introducing newer, faster, safer, and effective procedure for typing of microorganisms. A total of fifty shigella isolates were collected between November 2012 to October 2013 in Tehran, Iran. The strains were identified base on biochemical and molecular tests. Subsequently, all shigella species were confirmed by species-specific polymerase chain reaction (PCR). Virulence factors were detected using PCR for ial, set1A, and set1B genes. The strains were genotyped by MLVA typing method. All of the isolates were identified as S. sonnei by biochemical and molecular (PCR) methods. Virulence genes identified among all isolates included ial, and set1A genes in 20% and 5% of all isolates, respectively. On the other hand, none of isolates were positive for set1B gene. Using MLVA method 22 MLVA types were identified. MLVA type 11 accounted for 32% of isolates. Moreover, all virulence factors were only detected in MLVA type 11, 9, 5, 4. The results of this study indicate that the Iranian 2012-2013 S. sonnei outbreak isolates were virulent and clonaly related. Furthermore, this study showed that MLVA can be used as useful method for S. sonnei genotyping in epidemiological investigations.

Multi-locus sequence type analysis of Shigellas pp. isolates from Tehran, Iran

BACKGROUND AND OBJECTIVES

Strains of Shigella spp. can cause shigellosis, or bacillary dysentery. that is a public health problem worldwide. The aim of this study was to describe the population structure and genetic relatedness of multidrug resistant S. sonnei and S. flexneri isolated during a one year period from children with diarrhea in Tehran, Iran.

MATERIALS AND METHODS

A total of 70 Shigella spp. were detected during the study period. Twenty MDR isolates of Shigella spp. were randomly selected and used in this study. Bacterial identification was performed by conventional biochemical and serological and confirmed by molecular method. After antimicrobial susceptibility testing, we used Multilocus sequence typing (MLST) for subtyping isolates.

RESULTS

We found 14 Shigella sonnei and 6 Shigella flexneri isolates. Results of MLST showed five sequence types (ST) (145, 152, 241, 245, 1502) and BURST analysis revealed the largest number of single locus variant (SLV) and highest frequency (FREQ) for ST152. ST 152 with nine members was predicted as the founder by BURST. Frequency for ST 1502 and ST 245 was four isolates and the least frequency was seen for ST 241 and 145 with one and two members, respectively. ST 145 and ST 245 were described as singletons in BURST. All isolates with ST145 and ST245 were identified as Shigella flexneri.

CONCLUSION

Annual Multi locus sequence typing of MDR Shigella would help us in better understanding of dominant species and comparing our results with the same studies in other countries especially our neighbor countries in source tracking purposes.

Molecular Differentiation of Shigella Spp. from Enteroinvasive E. Coli

A real-time polymerase chain reaction (PCR) assay, amplifying the genes encoding lactose permease (lacY) and invasion plasmid antigen H (ipaH), was run on 121 isolates phenotypically classified as Shigella spp., enteroinvasive Escherichia coli (EIEC), or EIEC O nontypable (ONT). The results were compared with data from a generic E. coli multiple-locus variable-number of tandem repeat analysis (MLVA) and a Shigella MLVA.

The real-time PCR verified all Shigella spp. (n = 53) as Shigella (lacY negative) and all EIEC O121 (n = 15) and EIEC O124 (n = 2) as EIEC (lacY positive). However, the real-time PCR typed EIEC O164 as either EIEC (n = 2) or Shigella (n = 2) and, thus, was not suited for classifying this group of isolates. Interestingly, the majority (42/47, 89.4%) of the EIEC ONT were classified as Shigella (lacY negative) by the real-time PCR, and in nearly all cases, (92.9%, 39/42) data from both MLVA assays supported these findings. Overall, in 94.7% (114/121) of the isolates, the results from the real-time PCR were substantiated by the results from the MLVA assays.

In conclusion, the real-time PCR assay was fast and accurate in differentiating Shigella spp. from EIEC, with the exception of the EIEC O164 group. This molecular assay was particularly pragmatic for the challenging EIEC ONT group.

True Prevalence of Shigellosis in Indian Children with Acute Gastroenteritis: Have We Been Missing the Diagnosis?

BACKGROUND

Shigella is responsible for high morbidity and mortality among children, yet its true prevalence remains inconclusive. The aim of this study was to determine the actual prevalence of Shigella infection in childhood diarrhea and dysentery cases and assess the applicability of ipaH gene PCR in Indian settings.

METHODS

This study was conducted at Maulana Azad Medical College and associated Lok Nayak Hospital, New Delhi, India during 2011-12. A total of 385 children (207 with diarrhea, 118 with dysentery, and 60 matched controls) were enrolled. Stool samples were cultured, and the suspected colonies were analyzed using biochemical reactions and serotyping. Antimicrobial susceptibility testing was done using disc diffusion method. ipaH-gene PCR was performed directly on stool samples collected from 180 randomly selected patients (60 from each group).

RESULTS

Shigella was isolated using conventional culture methods in 8.2% (95% CI: 5.1%, 12.8%), 33.1% (95% CI: 25.2%, 42.0%), and 0% in the diarrhea, dysentery and control cases, respectively. High resistance was seen towards co-trimoxazole, nalidixic acid, fluoroquinolones, doxycycline and several beta-lactams drugs. Actual prevalence of shigellosis was determined using ipaH gene PCR to be 18.3% (95% CI: 10.4% - 30.1%) diarrhea cases and 56.7% (95% CI: 44.1, 68.4%) dysentery cases. One (1.7%, 95% CI: 0.01%, 9.7%) control specimen also yielded positive result in PCR.

CONCLUSIONS

Correct diagnosis of shigellosis is essential to start antimicrobial therapy in selected cases. The prevalence of Shigella / EIEC infection in children is much higher than previously estimated. Despite its high costs and other limitations, we recommend the use of ipaH-gene PCR as a routine tool in the management of childhood acute gastroenteritis cases.

Molecular diagnosis and anti-microbial resistance patterns among Shigella spp. isolated from patients with diarrhea

AIM

This study aims to determine the serogroup distribution and molecular diagnosis, as well as antimicrobial resistance profiles among Shigella spp. isolated from patients with diarrhea in Kerman, southeast of Iran.

BACKGROUND

Shigella species are frequent cause of bacterial dysentery worldwide. Previous studies have been reported that S. sonnei and S. flexneri are the most prevalent serogroups in various parts of Iran.

PATIENTS AND METHODS

A total of 624 stool samples were randomly collected from patients with diarrhea from June 2013 to August 2014. Biochemical and serological characterizations were performed for identifying Shigella spp. In addition, the multiplex PCR assay was carried out for the detection and differentiation of three pathogenic Shigella spp. Antibiotic susceptibility testing was performed according to the Clinical Laboratory Standards Institute (CLSI) guidelines.

RESULTS

Fifty six (9%) Shigella strains were isolated from stool samples. The most common species were S. flexneri 31(55.4%), followed by S . sonnei 18(32.1%) and S. boydii 7(12.5%). S. dysentery was not detected in the present study. All the isolates that identified by serological test as Shigella spp. were confirmed by the multiplex PCR method. The highest rate of resistance was observed for ampicillin and trimethoprim-sulphamethoxazole antibiotics with 52(92.9%) resistant, followed by tetracycline 44(78.6%) and cefotaxime 33(58.9%). All Shigella isolates were susceptible to ciprofloxacin. A significant relationship was found between the Shigella species and cefotaxime resistance (p<0.05).

CONCLUSION

S. flexneri was found as the most prevalent serogroup causing shigellosis. The high rate of resistance to third-generation cephalosporins limits the treatment options available for the management of shigellosis in Kerman, Iran.

Rapid and reliable discrimination between Shigella species and Escherichia coli using MALDI-TOF mass spectrometry

E. coli-Shigella species are a cryptic group of bacteria in which the Shigella species are distributed within the phylogenetic tree of E. coli. The nomenclature is historically based and the discrimination of these genera developed as a result of the epidemiological need to identify the cause of shigellosis, a severe disease caused by Shigella species. For these reasons, this incorrect classification of shigellae persists to date, and the ability to rapidly characterize E. coli and Shigella species remains highly desirable. Until recently, existing matrix-assisted laser desorption/ionization-time of flight mass spectrometry (MALDI-TOF MS) assays used to identify bacteria could not discriminate between E. coli and Shigella species. Here we present a rapid classification method for the E. coli-Shigella phylogroup based on MALDI-TOF MS which is supported by genetic analysis. E. coli and Shigella isolates were collected and genetically characterized by MLVA. A custom reference library for MALDI-TOF MS that represents the genetic diversity of E. coli and Shigella strains was developed. Characterization of E. coli and Shigella species is based on an approach with Biotyper software. Using this reference library it was possible to distinguish between Shigella species and E. coli. Of the 180 isolates tested, 94.4% were correctly classified as E. coli or shigellae. The results of four (2.2%) isolates could not be interpreted and six (3.3%) isolates were classified incorrectly. The custom library extends the existing MALDI-TOF MS method for species determination by enabling rapid and accurate discrimination between Shigella species and E. coli.

Relationship among Shigella spp. and enteroinvasive Escherichia coli (EIEC) and their differentiation

Shigellosis produces inflammatory reactions and ulceration on the intestinal epithelium followed by bloody or mucoid diarrhea. It is caused by enteroinvasive E. coli (EIEC) as well as any species of the genus Shigella, namely, S. dysenteriae, S. flexneri, S. boydii, and S. sonnei. This current species designation of Shigella does not specify genetic similarity. Shigella spp. could be easily differentiated from E. coli, but difficulties observed for the EIEC-Shigella differentiation as both show similar biochemical traits and can cause dysentery using the same mode of invasion. Sequencing of multiple housekeeping genes indicates that Shigella has derived on several different occasions via acquisition of the transferable forms of ancestral virulence plasmids within commensal E. coli and form a Shigella-EIEC pathovar. EIEC showed lower expression of virulence genes compared to Shigella, hence EIEC produce less severe disease than Shigella spp. Conventional microbiological techniques often lead to confusing results concerning the discrimination between EIEC and Shigella spp. The lactose permease gene (lacY) is present in all E. coli strains but absent in Shigella spp., whereas β-glucuronidase gene (uidA) is present in both E. coli and Shigella spp. Thus uidA gene and lacY gene based duplex real-time PCR assay could be used for easy identification and differentiation of Shigella spp. from E. coli and in particular EIEC.

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.

A novel multiplex PCR for the simultaneous detection of Salmonella enterica and Shigella species

Salmonella enterica and Shigella species are commonly associated with food and water borne infections leading to gastrointestinal diseases. The present work was undertaken to develop a sensitive and reliable PCR based detection system for simultaneous detection of Salmonella enterica and Shigella at species level. For this the conserved regions of specific genes namely ipaH1, ipaH, wbgZ, wzy and invA were targeted for detection of Shigella genus, S. flexneri, S. sonnei, S. boydii and Salmonella enterica respectively along with an internal amplification control (IAC). The results showed that twenty Salmonella and eleven Shigella spp., were accurately identified by the assay without showing non-specificity against closely related other Enterobacteriaceae organisms and also against other pathogens. Further evaluation of multiplex PCR was undertaken on 50 natural samples of chicken, eggs and poultry litter and results compared with conventional culture isolation and identification procedure. The multiplex PCR identified the presence of Salmonella and Shigella strains with a short pre-enrichment step of 5 h in peptone water and the same samples were processed by conventional procedures for comparison. Therefore, this reported multiplex PCR can serve as an alternative to the tedious time-consuming procedure of culture and identification in food safety laboratories.

New high-affinity monoclonal antibodies against Shiga toxin 1 facilitate the detection of hybrid Stx1/Stx2 in vivo

BACKGROUND

Shiga toxin-producing E. coli (STEC) are a group of common and potentially deadly intestinal pathogens expressing Shiga toxin (Stx) as a primary virulence factor. Of the two types of Stx, Stx2 is responsible for more severe symptoms during infection, while Stx1 is almost identical to the Shiga toxin from Shigella dysenteriae, a ubiquitous pathogen in developing countries. Although antibodies against Stx1 have been reported, few have reached the affinity needed for assembling highly sensitive immunoassays. Sensitive and affordable immunoassays for Stx1 and Stx2 could help improve detection of STEC in livestock, food, the environment, and in clinical samples resulting in improved food safety and human health.

METHOD AND FINDINGS

Three new monoclonal antibodies (mAbs) against the B subunit of Stx1 were generated using recombinant toxoid Stx1E167Q and hybridoma technology. These new mAbs recognize all subtypes of Stx1, but do not cross-react with any subtype of Stx2. In addition, they exhibited the ability to neutralize Stx1 toxicity in Vero cell assays. An optimized sandwich ELISA using of a pair of these mAbs had a limit of detection of 8.7 pg/mL, which is superior to any existing assay of this kind. Using one of these Stx1 mAbs in concert with Stx2 mAbs, the presence of hybrid Stx1/Stx2 toxin in the culture media of STEC strains that express both Stx1 and Stx2 was demonstrated.

CONCLUSIONS

These new mAbs provide a mix of availability, utility, versatility, and most importantly, increased sensitivity for detection of Stx1. There are numerous potential applications for these mAbs, including low-cost detection assays and therapeutic use. Analysis of hybrid Stx1/2 could provide new insights on the structure, activity, and cellular targets of Shiga toxins.

Isolation and molecular characterization of Salmonella enterica, Escherichia coli O157:H7 and Shigella spp. from meat and dairy products in Egypt

Foodborne pathogens are a major threat to food safety, especially in developing countries where hygiene and sanitation facilities are often poor. Salmonella enterica, Escherichia coli O157:H7 and Shigella spp. are among the major causes of outbreaks of foodborne diseases. This large-scale study investigated the prevalence of these foodborne pathogens in meat (beef and chicken) and dairy products collected from street vendors, butchers, retail markets and slaughterhouses in Egypt. A total of 1600 food samples (800 meat products and 800 dairy products) were analyzed using culture and PCR based methods. S. enterica, E. coli O157:H7 and Shigella spp. were detected in 69 (4.3%), 54 (3.4%) and 27 (1.7%) samples respectively. S. enterica serovar Typhimurium, S. enterica serovar Enteritidis, S. enterica serovar Infantis and non-typable serovars were detected in 28 (1.8%), 22 (1.4%), 16 (1.0%) and 3 (0.1%) samples respectively. All E. coli O157:H7 isolates were positive for stx1 and/or stx2 virulence toxin genes. Shigella flexneri, Shigella sonnei and Shigella dysenteriae were detected in 18 (1.2%), 7 (0.4%) and 2 (0.1%) samples respectively. The incidences of S. enterica and Shigella spp. were higher in meat products (53; 6.6% and 16; 2.0%, respectively) than in dairy products (16; 2.0% and 11; 1.4%, respectively), while, E. coli O157:H7 was higher in dairy products (29; 3.6%) than in meat products (25; 3.1%). The incidence of foodborne pathogens in meat and dairy products was determined in a large-scale survey in Africa.