Population structure analysis and laboratory monitoring of Shigella by core-genome multilocus sequence typing

High carriage and possible hidden spread of multidrug-resistant Salmonella among asymptomatic workers in Yulin, China

Food workers have frequent contact with unprocessed foods, but their carriage of Salmonella and potential influence on public health have not been comprehensively assessed. We investigated Salmonella carriage among food workers compared with non-food workers based on occupational health screening of 260,315 asymptomatic workers over an 8-year surveillance period in Yulin, China. We confirmed that healthy carriers serve as natural reservoirs for Salmonella, with higher carriage rates in food workers than non-food workers. The isolates from food workers also exhibited greater serovar diversity and likely higher levels of antimicrobial resistance than those from non-food workers. Factors such as meteorological, social, and hygiene factors potentially influenced the carriage rate. Genomic analysis revealed a consistent increase in antimicrobial resistance genes among Salmonella isolates over the study period, with the majority of these antimicrobial resistance genes located on plasmids. Additionally, we identified numerous closely related bacterial clusters, which might reflect clusters of hidden local foodborne infections. This study underscores the elevated risk posed by food workers in the persistence and dissemination of Salmonella as vectors/fomites. Enhanced monitoring and targeted interventions in this group may reduce the dissemination of pathogens and antimicrobial resistance genes.

Genome and antibiotic resistance characteristics of Shigella clinical isolates in Fujian Province, Southeast China, 2005-2019

Shigellosis is a serious public health issue in many developing countries. The emergence of multidrug-resistant (MDR) Shigella isolates has deepened the treatment difficulty and health burden of shigellosis. China is the largest developing country in the world, but so far, the genome of MDR Shigella isolates has not been well characterized. In this study, 60 clinical isolates of Shigella spp. in Fujian Province, southeast China, from 2005 to 2019 were characterized for drug resistance phenotype, whole-genome sequencing and bioinformatics analysis. The results showed that the MDR rate of Shigella isolates was 100%, among which the resistance rates of cefotaxime, ciprofloxacin and azithromycin were 36.67, 21.67 and 10.00 %, respectively. The positive rate of extended-spectrum beta-lactamase (ESBL)-producing strains was 23.33%. The resistance profiles of Shigella flexneri and Shigella sonnei to some antimicrobials differed. The MDR isolates carried multiple antimicrobial resistance genes, among which blaCTX-M-14 and blaCTX-M-15 mediated ESBL resistance. 'ISEcp1 -blaCTX-M -IS903' (type I) and 'ISEcp1 -blaCTX-M' (type II) were the most common genetic environments around the blaCTX-M genes, and plasmids containing these structures included IncFII, IncI1, IncI2 and IncN. The double gene mutation pattern of gyrA and parC resulted in a significant decrease in the sensitivity of S. flexneri to ciprofloxacin. The overall resistance phenotype and genotype concordance rate was 88.50%, and the sensitivity and specificity of the genotype antimicrobial susceptibility test (AST) were 93.35 and 82.53 %, respectively. However, inconsistency occurred between phenotypic and genotype profiles for a few antibiotics. Phylogenomic investigation with core genome multi-locus sequence typing (cgMLST) and SNPs were used to characterize the endemic transmission of these infections in Fujian and their evolutionary origin within the global context. For S. flexneri, Fujian isolates were all limited to PG3 and could be divided into three phylogenetic clusters. The ciprofloxacin-resistant strains were mainly F2a and FXv and assigned to the three clusters with different quinolone resistance-determining region mutation patterns. For S. sonnei, most Fujian strains belonged to Lineage III with genotype 3.7.6, except three isolates of Lineage I with genotype 1.3. The strains carrying the blaCTX-M genes were dispersed, indicating different origins of gene acquisition. Most of the circulating isolates in Fujian Province were not related to major international outbreak lineages and were only endemic to the country. In conclusion, multi-drug resistance of Shigella isolates in Fujian Province was serious, and genome-based laboratory surveillance will be crucial to the clinical treatment and public health measures for shigellosis.

High-Throughput Luminescence-Based Serum Bactericidal Assay Optimization and Characterization to Assess Human Sera Functionality Against Multiple Shigella flexneri Serotypes

Shigellosis represents a significant global health concern particularly affecting children under 5 years in low- and middle-income countries (LMICs) and is associated with stunting and antimicrobial resistance. There is a critical need for an effective vaccine offering broad protection against the different Shigella serotypes. A correlate of protection has not yet been established but there is a general consensus about the relevant role of anti-O-Antigen-specific IgG and its functionality evaluated by the Serum Bactericidal Assay (SBA). This study aims to characterize a high-throughput luminescence-based SBA (L-SBA) against seven widespread Shigella serotypes. The assay was previously developed and characterized for S. sonnei and S. flexneri 1b, 2a, and 3a and has now been refined and extended to an additional five serotypes (S. flexneri 4a, 5b, 6, X, and Y). The characterization of the assay with human sera confirmed the repeatability, intermediate precision, and linearity of the assays; both homologous and heterologous specificity were verified as well; finally, limit of detection and quantification were established for all assays. Moreover, different sources of baby rabbit complement showed to have no impact on L-SBA output. The results obtained confirm the possibility of extending the L-SBA to multiple Shigella serotypes, thus enabling analysis of the functional response induced by natural exposure to Shigella in epidemiological studies and the ability of candidate vaccines to elicit cross-functional antibodies able to kill a broad panel of prevalent Shigella serotypes in a complement-mediated fashion.

Genomic analysis of Shigella isolates from Lebanon reveals marked genetic diversity and antimicrobial resistance

In this study, we characterized 54 clinical isolates of Shigella collected in North Lebanon between 2009 and 2017 through phenotypic and genomic analyses. The most prevalent serogroup was S. sonnei, accounting for 46.3 % (25/54) of the isolates, followed by S. flexneri (27.8 %, 15/54), S. boydii (18.5 %, 10/54) and S. dysenteriae (7.4 %, 4/54). Only three isolates were pan-susceptible, and 87 % (47/54) of the isolates had multidrug resistance phenotypes. Notably, 27.8 % (15/54) of the isolates were resistant to third-generation cephalosporins (3GCs) and 77.8 % (42/54) were resistant to nalidixic acid. 3GC resistance was mediated by the extended-spectrum beta-lactamase genes bla CTX-M-15 and bla CTX-M-3, which were present on various plasmids. Quinolone resistance was conferred by single point mutations in the gyrA DNA gyrase gene, leading to GyrA S83L, GyrA D87Y or GyrA S83A amino acid substitutions. This is the first study, to our knowledge, to provide genomic insights into the serotypes of Shigella circulating in Lebanon and the various antimicrobial resistance determinants carried by these strains.

Concordance between Genotypic and Phenotypic Drug-Resistant Profiles of Shigella Isolates from Taiyuan City, Shanxi Province, China, 2005 to 2016

Antimicrobial resistance in Shigella spp. is a global public health concern. In this study, the AMR phenotypic profiles of 10 kinds of antibiotics were compared with the genotypic profiles using genomic analysis of 218 Shigella isolates from Taiyuan City, Shanxi Province, China, 2005 to 2016. Core genome Multilocus Sequence Typing (cgMLST) based on the EnteroBase Escherichia/Shigella scheme was used to obtain the genetic relatedness of Shigella isolates. Multiple-drug resistance was observed in 96.79% Shigella spp., and the resistance to antimicrobial agents varied between S. flexneri and S. sonnei. The genotypic results correlated well with the phenotypic profiles with concordance rates of 96.42% and 94.50% in S. flexneri and S. sonnei isolates, respectively, from Taiyuan City, Shanxi Province. The sensitivity and specificity of the genotypic antimicrobial susceptibility testing (AST) were 97.56% and 95.34% for S. flexneri, and 95.65% and 93.31% for S. sonnei isolates, respectively. A discrepancy of genotypic and phenotypic AST results existed in some cephalosporin- and azithromycin-resistant Shigella isolates; there were no clear resistance patterns to predict ciprofloxacin resistance. There were major discrepancies between genotypic and phenotypic AST in the genotypically resistant but phenotypically susceptible isolates. The drug-resistance patterns and essential drug-resistance genes to predict the phenotypic drug-resistant profiles were the discrepancies between S. flexneri and S. sonnei isolates. Phylogenetic analysis showed that isolates of the same cluster but with different antibiotic-resistance gene patterns occurred because of the loss or gain of antibiotic-resistance genes located in the plasmids and multidrug-resistance islands. IMPORTANCE Antimicrobial resistance in Shigella spp. has become a global public health concern. In this study, we identified the antimicrobial susceptibility testing (AST) characteristics based on genomic sequences of 218 Shigella isolates and analyzed the correlation between genotypic and phenotypic antibiotic resistance profiles of Shigella spp., especially for fluoroquinolone, macrolides, and third-generation cephalosporins. Our results show that the genotypic results correlated with the phenotypic profiles with concordance rates of 96.42% and 94.50% in S. flexneri and S. sonnei isolates, respectively. The drug-resistance patterns and essential drug-resistance genes to predict the phenotypic drug-resistant profiles of S. flexneri and S. sonnei isolates in Taiyuan city were distinct. The discrepancy between genotypic and phenotypic AST was considerable in the genotypically resistant but phenotypically susceptible isolates. The information on drug resistance and resistance genes in this study can offer more details on the prevalence of drug resistance of Shigella spp.

Genomes-based MLST, cgMLST, wgMLST and SNP analysis of Salmonella Typhimurium from animals and humans

Salmonella Typhimurium (S. Typhimurium) is an important food-borne and zoonotic pathogen that causes salmonellosis. With the development of whole genome sequencing (WGS), genome-based typing has been widely applied to bacteriology. In this study, we investigated genotyping and phylogenetic clusters of S. Typhimurium isolates from humans and animals in different provinces (including Beijing, Shandong, Guangxi, Shaanxi, Henan, and Shanghai) of China during 2009-2018 using multi locus sequence typing (MLST), core genome MLST (cgMLST), whole genome MLST (wgMLST) and single nucleotide polymorphism (SNP) based on WGS. 29 S. Typhimurium isolates from chicken (n = 22), sick pigeon (n = 2), patients (n = 4) and sick swine (n = 1) were tested. MLST analysis showed S. Typhimurium strains were divided into four STs, namely ST19 (n = 14), ST34 (n = 12), ST128 (n = 2) and ST1544 (n = 1). cgMLST and wgMLST divided 29 strains into 27 cgSTs and 29 wgST, respectively. Phylogenetic clustering showed that all isolates were divided into 4 clusters and 4 singletons. SNP analysis was used to examine MLST, cgMLST, wgMLST analysis. Finally, comparisons of MLST, cgMLST, wgMLST, and SNP were analyzed and the results showed their precision increased in order. In summary, genomic typing and phylogenetic relationships of 29 S. Typhimurium strains from different sources in China were analyzed. These findings were beneficial to investigate molecular pathogenesis, bacterial diversity, and traceability analysis of Salmonella.

Characterization of Shigella flexneri Serotype 6 Strains Isolated from Bangladesh and Identification of a New Phylogenetic Cluster

A significant cause of shigellosis in Bangladesh and other developing countries is Shigella flexneri serotype 6. This serotype has been subtyped, on the basis of the absence or presence of a group-specific antigen, E1037, into S. flexneri 6a and 6b, respectively. Here, we provided rationales for the subclassification, using several phenotypic and molecular tools. A set of S. flexneri 6a and 6b strains isolated between 1997 and 2015 were characterized by analyzing their biochemical properties, plasmid profiles, virulence markers, pulsed-field gel electrophoresis (PFGE) results, and ribotype. Additionally, the genomic relatedness of these subserotypes was investigated with global isolates of serotype 6 using publicly available genomes. Both subserotypes of S. flexneri 6 agglutinated with monoclonal antiserum against S. flexneri (MASF) B and type VI-specific antiserum (MASF VI) and were PCR positive for O-antigen flippase-specific genes and virulence markers (ipaH, ial, sen, and sigA). Unlike S. flexneri 6a strains, S. flexneri 6b strains seroagglutinated with anti-E1037 antibodies, MASF IV-I. Notably, these two antigenically distinct subserotypes were clonally diverse, showing two distinct PFGE patterns following the digestion of chromosomal DNA with either XbaI or IceuI. In addition, hybridization of a 16S rRNA gene probe with HindIII-digested genomic DNA yielded two distinguishing ribotypes. Genomic comparison of S. flexneri subserotype 6a and 6b strains from Bangladesh indicated that, although these strains were in genomic synteny, the majority of them formed a unique phylogroup (PG-4) that was missing for the global isolates. This study supports the subserotyping and emphasizes the need for global monitoring of the S. flexneri subserotypes 6a and 6b. IMPORTANCE Shigella flexneri serotype 6 is one of the predominant serotypes among shigellosis cases in Bangladesh. Characterization of a novel subserotype of S. flexneri 6 (VI:E1037), agglutinated with type 6-specific antibody and anti-E1037, indicates a unique evolutionary ancestry. PFGE genotyping supports the finding that these two antigenically distinct subserotypes are clonally diverse. A phylogenetic study based on single-nucleotide polymorphism (SNP) data revealed that these two subserotypes were in genomic synteny, although their genomes were reduced. Interestingly, a majority of the S. flexneri 6 strains isolated from Bangladesh form a novel phylogenetic cluster. Therefore, this report underpins the global monitoring and tracking of the novel subserotype.

Rapid emergence of extensively drug-resistant Shigella sonnei in France

Shigella sonnei, the main cause of bacillary dysentery in high-income countries, has become increasingly resistant to antibiotics. We monitored the antimicrobial susceptibility of 7121 S. sonnei isolates collected in France between 2005 and 2021. We detected a dramatic increase in the proportion of isolates simultaneously resistant to ciprofloxacin (CIP), third-generation cephalosporins (3GCs) and azithromycin (AZM) from 2015. Our genomic analysis of 164 such extensively drug-resistant (XDR) isolates identified 13 different clusters within CIP-resistant sublineage 3.6.1, which was selected in South Asia ∼15 years ago. AZM resistance was subsequently acquired, principally through IncFII (pKSR100-like) plasmids. The last step in the development of the XDR phenotype involved various extended-spectrum beta-lactamase genes (bla_CTX-M-3, bla_CTX-M-15, bla_CTX-M-27, bla_CTX-M-55, and bla_CTX-M-134) carried by different plasmids (IncFII, IncI1, IncB/O/K/Z) or even integrated into the chromosome, and encoding resistance to 3GCs. This rapid emergence of XDR S. sonnei, including an international epidemic strain, is alarming, and good laboratory-based surveillance of shigellosis will be crucial for informed decision-making and appropriate public health action.

Analysis of Genetic Relatedness between Gastric and Oral Helicobacter pylori in Patients with Early Gastric Cancer Using Multilocus Sequence Typing

The oral cavity is the second most colonized site of Helicobacter pylori after the stomach. This study aimed to compare the genetic relatedness between gastric and oral H. pylori in Japanese patients with early gastric cancer through multilocus sequence typing (MLST) analysis using eight housekeeping genes. Gastric biopsy specimens and oral samples were collected from 21 patients with a fecal antigen test positive for H. pylori. The number of H. pylori allelic profiles ranged from zero to eight since the yield of DNA was small even when the nested PCR was performed. MLST analysis revealed that only one patient had a matching oral and gastric H. pylori genotype, suggesting that different genotypes of H. pylori inhabit the oral cavity and gastric mucosa. The phylogenetic analysis showed that oral H. pylori in six patients was similar to gastric H. pylori, implying that the two strains are related but not of the same origin, and those strains may be infected on separate occasions. It is necessary to establish a culture method for oral H. pylori to elucidate whether the oral cavity acts as the source of gastric infection, as our analysis was based on a limited number of allele sequences.

An ST131 clade and a phylogroup A clade bearing an O101-like O-antigen cluster predominate among bloodstream Escherichia coli isolates from South-West Nigeria hospitals

Escherichia coli bloodstream infections are typically attributed to a limited number of lineages that carry virulence factors associated with invasiveness. In Nigeria, the identity of circulating clones is largely unknown and surveillance of their antimicrobial resistance has been limited. We verified and whole-genome sequenced 68 2016-2018 bloodstream E. coli isolates from three sentinel sites in South-Western Nigeria and susceptibility tested 67 of them. Resistance to antimicrobials commonly used in Nigeria was high, with 67 (100 %), 62 (92.5 %), 53 (79.1 %) and 37 (55.2 %) showing resistance to trimethoprim, ampicillin, ciprofloxacin and aminoglycosides, respectively. Thirty-five (51 %) isolates carried extended-spectrum β-lactamase genes and 32 (91 %) of these were multidrug resistant. All the isolates were susceptible to carbapenems and colistin. The strain set included globally disseminated high-risk clones from sequence type (ST)12 (2), ST131 (12) and ST648 (4). Twenty-three (33.8 %) of the isolates clustered within two clades. The first of these consisted of ST131 strains, comprising O16:H5 and O25:H4 sub-lineages. The second was an ST10-ST167 complex clade comprising strains carrying O-antigen and capsular genes of likely Klebsiella origin, identical to those of avian pathogenic E. coli Sanji, and serotyped in silico as O89, O101 or ONovel32, depending on the tool used. Four temporally associated ST90 strains from one sentinel were closely related enough to suggest that at least some of them represented a retrospectively detected outbreak cluster. Our data implicate a broad repertoire of E. coli isolates associated with bloodstream infections in South-West Nigeria. Continued genomic surveillance is valuable for tracking clones of importance and for outbreak identification.

EnteroBase: hierarchical clustering of 100 000s of bacterial genomes into species/subspecies and populations

The definition of bacterial species is traditionally a taxonomic issue while bacterial populations are identified by population genetics. These assignments are species specific, and depend on the practitioner. Legacy multilocus sequence typing is commonly used to identify sequence types (STs) and clusters (ST Complexes). However, these approaches are not adequate for the millions of genomic sequences from bacterial pathogens that have been generated since 2012. EnteroBase (http://enterobase.warwick.ac.uk) automatically clusters core genome MLST allelic profiles into hierarchical clusters (HierCC) after assembling annotated draft genomes from short-read sequences. HierCC clusters span core sequence diversity from the species level down to individual transmission chains. Here we evaluate HierCC's ability to correctly assign 100 000s of genomes to the species/subspecies and population levels for Salmonella, Escherichia, Clostridoides, Yersinia, Vibrio and Streptococcus. HierCC assignments were more consistent with maximum-likelihood super-trees of core SNPs or presence/absence of accessory genes than classical taxonomic assignments or 95% ANI. However, neither HierCC nor ANI were uniformly consistent with classical taxonomy of Streptococcus. HierCC was also consistent with legacy eBGs/ST Complexes in Salmonella or Escherichia and with O serogroups in Salmonella. Thus, EnteroBase HierCC supports the automated identification of and assignment to species/subspecies and populations for multiple genera. This article is part of a discussion meeting issue 'Genomic population structures of microbial pathogens'.

Application and challenge of bacteriophage in the food protection

In recent years, foodborne diseases caused by pathogens have been increasing. Therefore, it is essential to control the growth and transmission of pathogens. Bacteriophages (phages) have the potential to play an important role in the biological prevention, control, and treatment of these foodborne diseases due to their favorable advantages. Phages not only effectively inhibit pathogenic bacteria and prolong the shelf life of food, but also possess the advantages of specificity and an absence of chemical residues. Currently, there are many cases of phage applications in agriculture, animal disease prevention and control, food safety, and the treatment of drug-resistant disease. In this review, we summarize the recent research progress on phages against foodborne pathogenic bacteria, including Escherichia coli, Salmonella, Campylobacter, Listeria monocytogenes, Shigella, Vibrio parahaemolyticus, and Staphylococcus aureus. We also discuss the main issues and their corresponding solutions in the application of phages in the food industry. In recent years, although researchers have discovered more phages with potential applications in the food industry, most researchers use these phages based on their host spectrum, and the application environment is mostly in the laboratory. Therefore, the practical application of these phages in different aspects of the food industry may be unsatisfactory and even have some negative effects. Thus, we suggest that before using these phages, it is necessary to identify their specific receptors. Using their specific receptors as the selection basis for their application and combining phages with other phages or phages with traditional antibacterial agents may further improve their safety and application efficiency. Collectively, this review provides a theoretical reference for the basic research and application of phages in the food industry.

Virulence plasmid pINV as a genetic signature for Shigella flexneri phylogeny

Shigella flexneri is a major health burden in low- and middle-income countries, where it is a leading cause of mortality associated with diarrhoea in children, and shows an increasing incidence among travellers and men having sex with men. Like all Shigella spp., S. flexneri has evolved from commensal Escherichia coli following the acquisition of a large plasmid pINV, which contains genes essential for virulence. Current sequence typing schemes of Shigella are based on combinations of chromosomal genetic loci, since pINV-encoded virulence genes are often lost during growth in the laboratory, making these elements inappropriate for sequence typing. By performing comparative analysis of pINVs from S. flexneri strains isolated from different geographical regions and belonging to different serotypes, we found that in contrast to plasmid-encoded virulence genes, plasmid maintenance genes are highly stable pINV-encoded elements. For the first time, to our knowledge, we have developed a S. flexneri plasmid multilocus sequence typing (pMLST) method based on different combinations of alleles of the vapBC and yacAB toxin–antitoxin (TA) systems, and the parAB partitioning system. This enables typing of S. flexneri pINV plasmids into distinct ‘virulence sequence types’ (vSTs). Furthermore, the phylogenies of vST alleles and bacterial host core genomes suggests an intimate co-evolution of pINV with the chromosome of its bacterial host, consistent with previous findings. This work demonstrates the potential of plasmid maintenance loci as genetic characteristics to study as well as to trace the molecular phylogenesis of S. flexneri pINV and the phylogenetic relationship of this plasmid with its bacterial host.

The Notable Achievements and the Prospects of Bacterial Pathogen Genomics

Throughout the entirety of human history, bacterial pathogens have played an important role and even shaped the fate of civilizations. The application of genomics within the last 27 years has radically changed the way we understand the biology and evolution of these pathogens. In this review, we discuss how the short- (Illumina) and long-read (PacBio, Oxford Nanopore) sequencing technologies have shaped the discipline of bacterial pathogen genomics, in terms of fundamental research (i.e., evolution of pathogenicity), forensics, food safety, and routine clinical microbiology. We have mined and discuss some of the most prominent data/bioinformatics resources such as NCBI pathogens, PATRIC, and Pathogenwatch. Based on this mining, we present some of the most popular sequencing technologies, hybrid approaches, assemblers, and annotation pipelines. A small number of bacterial pathogens are of very high importance, and we also present the wealth of the genomic data for these species (i.e., which ones they are, the number of antimicrobial resistance genes per genome, the number of virulence factors). Finally, we discuss how this discipline will probably be transformed in the near future, especially by transitioning into metagenome-assembled genomes (MAGs), thanks to long-read sequencing.