Phylogenomics and antimicrobial resistance of Salmonella Typhi and Paratyphi A, B and C in England, 2016-2019.

The emergence of antimicrobial resistance (AMR) to first- and second-line treatment regimens of enteric fever is a global public-health problem, and routine genomic surveillance to inform clinical and public-health management guidance is essential. Here, we present the prospective analysis of genomic data to monitor trends in incidence, AMR and travel, and assess hierarchical clustering (HierCC) methodology of 1742 isolates of typhoidal salmonellae. Trend analysis of Salmonella Typhi and S. Paratyphi A cases per year increased 48 and 17.3%, respectively, between 2016 and 2019 in England, mainly associated with travel to South Asia. S. Paratyphi B cases have remained stable and are mainly associated with travel to the Middle East and South America. There has been an increase in the number of S. Typhi exhibiting a multidrug-resistant (MDR) profile and the emergence of extensively drug resistant (XDR) profiles. HierCC was a robust method to categorize clonal groups into clades and clusters associated with travel and AMR profiles. The majority of cases that had XDR S. Typhi reported recent travel to Pakistan (94 %) and belonged to a subpopulation of the 4.3.1 (H58) clone (HC5_1452). The phenotypic and genotypic AMR results showed high concordance for S. Typhi and S. Paratyphi A, B and C, with 99.99 % concordance and only three (0.01 %) discordant results out of a possible 23 178 isolate/antibiotic combinations. Genomic surveillance of enteric fever has shown the recent emergence and increase of MDR and XDR S. Typhi strains, resulting in a review of clinical guidelines to improve management of imported infections.

ESBL-producing strains isolated from imported cases of enteric fever in England and Wales reveal multiple chromosomal integrations of blaCTX-M-15 in XDR Salmonella Typhi.

BACKGROUND: There are approximately 300 cases of enteric fever reported annually from England and Wales; most are imported infections. Clinical management of enteric fever remains a challenge with the emergence of ESBL-producing strains, especially XDR Salmonella Typhi from Sindh, Pakistan. METHODS: All strains of S. Typhi and Salmonella Paratyphi A isolated from cases presenting with symptoms of enteric fever in England and Wales, between 1 April 2014 and 31 March 2020, were characterized using WGS. Antibiotic susceptibility testing was performed using an agar dilution method. RESULTS: ESBL strains contributed to 69 cases of enteric fever (S. Typhi n = 68, S. Paratyphi A n = 1); 68 were imported (Pakistan n = 64, Iraq n = 2, Bangladesh n = 1 and India n = 1). Ages ranged from 1 to 56 years, 36/69 (52%) were children, 52% were female and the duration of hospital stay ranged from 1 to 23 days. The ESBL phenotype was conferred by the presence of blaCTX-M-15 (S. Typhi n = 67 and S. Paratyphi A n = 1) or blaCTX-M-55 (S. Typhi n = 1). An IncY plasmid harbouring blaCTX-M-15 and qnr was detected in 56 strains from Pakistan. The IncY plasmid was absent in the remaining strains and there was evidence of a 4 kb ISEcpl-blaCTX-M-15-tnp gene cassette insertion into the chromosome at one of three integration points. CONCLUSIONS: Chromosomal integration of blaCTX-M-15 within the XDR Sindh strains may lead to the maintenance of resistance in the absence of antibiotic selection pressure. Empirical treatment of cases of complicated enteric fever returning from Pakistan will henceforth have to include a carbapenem.

Antimicrobial resistance in Shiga toxin-producing Escherichia coli other than serotype O157 : H7 in England, 2014-2016.

Introduction. Despite many ongoing surveillance projects and the recent focus on the veterinary and clinical 'One Health' aspects of antimicrobial resistance (AMR), evidence of the extent of any public health risk posed by animal reservoirs with respect to the transmission of resistant strains of Escherichia coli to humans remains varied and contentious. In the UK, the main zoonotic reservoir for the foodborne pathogen Shiga toxin-producing E. coli (STEC) is cattle and sheep. In this study, we adopt an alternative approach to the risk assessment of transmission of AMR E. coli from animals to humans, involving monitoring AMR in isolates of STEC, an established zoonotic, foodborne pathogen, from human cases of gastrointestinal disease.Aim. The aim of this study was to determine the genome-derived AMR profiles for STEC from human cases to assess the risk of transmission of multidrug-resistant STEC from ruminants to humans.Methodology. STEC belonging to 10 different clonal complexes (CCs) (n=457) isolated from human faecal specimens were sequenced and genome-derived AMR profiles were determined. Phenotypic susceptibility testing was undertaken on all isolates (n=100) predicted to be resistant to at least one class of antimicrobial.Results. Of the 457 isolates, 332 (72.7 %) lacked identifiable resistance genes and were predicted to be fully susceptible to 11 classes of antimicrobials; 125/332 (27.3 %) carried 1 or more resistance genes, of which 83/125 (66.4 %) were resistant to 3 or more classes of antibiotic. The percentage of isolates harbouring AMR determinants varied between CCs, from 4% in CC25 to 100% in CC504. Forty-six different AMR genes were detected, which conferred resistance to eight different antibiotic classes. Resistance to ampicillin, streptomycin, tetracyclines and sulphonamides was most commonly detected. Four isolates were identified as extended-spectrum ß-lactamase producers. An overall concordance of 97.7 % (n=1075/1100) was demonstrated between the phenotypic and genotypic methods.Conclusion. This analysis provided an indirect assessment of the risk of transmission of AMR gastrointestinal pathogens from animals to humans, and revealed a subset of human isolates of the zoonotic pathogen STEC were resistant to the antimicrobials used in animal husbandry. However, this proportion has not increased over the last three decades, and thismay provide evidence that guidancepromoting responsible practice has been effective.

A real-time multiplex PCR for the identification and typing of Vibrio cholerae.

We report the development and validation of a duo-triplex real-time polymerase chain reaction (PCR) for the rapid identification and typing of Vibrio cholerae. The PCR assay targets a species-specific toxR gene present in all strains of V. cholerae and used as a marker for the species wbeO1 and wbfO139, encoding the O1 and O139 somatic antigens, and ctxA, encoding cholera toxin (CT). The two tcpA variants associated with the classical and El-Tor biotypes are used to infer biotype. The assay was evaluated using 178 isolates comprising eight different Vibrio species, including 122 isolates of V. cholerae. The PCR results of 171/178 (96.1%) isolates were concordant with the serotyping, biotyping, and expected CT results. Variants of toxR (n=3), nonfunctional wbeO1 (n=1), and CT-negative isolates of V. cholerae O1 (n=3) were likely explanations for the mismatched results. This duo-triplex real-time PCR is a reproducible and robust assay for the rapid identification and typing of V. cholerae belonging to the highly pathogenic, pandemic lineages.

Whole-Genome Sequencing for National Surveillance of Shigella flexneri.

National surveillance of Shigella flexneri ensures the rapid detection of outbreaks to facilitate public health investigation and intervention strategies. In this study, we used whole-genome sequencing (WGS) to type S. flexneri in order to detect linked cases and support epidemiological investigations. We prospectively analyzed 330 isolates of S. flexneri received at the Gastrointestinal Bacteria Reference Unit at Public Health England between August 2015 and January 2016. Traditional phenotypic and WGS sub-typing methods were compared. PCR was carried out on isolates exhibiting phenotypic/genotypic discrepancies with respect to serotype. Phylogenetic relationships between isolates were analyzed by WGS using single nucleotide polymorphism (SNP) typing to facilitate cluster detection. For 306/330 (93%) isolates there was concordance between serotype derived from the genome and phenotypic serology. Discrepant results between the phenotypic and genotypic tests were attributed to novel O-antigen synthesis/modification gene combinations or indels identified in O-antigen synthesis/modification genes rendering them dysfunctional. SNP typing identified 36 clusters of two isolates or more. WGS provided microbiological evidence of epidemiologically linked clusters and detected novel O-antigen synthesis/modification gene combinations associated with two outbreaks. WGS provided reliable and robust data for monitoring trends in the incidence of different serotypes over time. SNP typing can be used to facilitate outbreak investigations in real-time thereby informing surveillance strategies and providing the opportunities for implementing timely public health interventions.

Whole Genome Sequencing for Public Health Surveillance of Shiga Toxin-Producing Escherichia coli Other than Serogroup O157.

Shiga toxin-producing Escherichia coli (STEC) are considered to be a significant threat to public health due to the severity of gastrointestinal symptoms associated with human infection. In England STEC O157 is the most commonly detected STEC serogroup, however, the implementation of PCR at local hospital laboratories has resulted in an increase in the detection of non-O157 STEC. The aim of this study was to evaluate the use of whole genome sequencing (WGS) for routine public health surveillance of non-O157 STEC by comparing this approach to phenotypic serotyping and PCR for subtyping the stx-encoding genes. Of the 102 isolates where phenotypic and genotypic serotyping could be compared, 98 gave fully concordant results. The most common non-O157 STEC serogroups detected were O146 (22) and O26 (18). All but one of the 38 isolates that could not be phenotypically serotyped (designated O unidentifiable or O rough) were serotyped using the WGS data. Of the 73 isolates where a flagella type was available by traditional phenotypic typing, all results matched the H-type derived from the WGS data. Of the 140 sequenced non-O157 isolates, 52 (37.1%) harboured stx1 only, 42 (30.0%) had stx2 only, 46 (32.9%) carried stx1 and stx2. Of these, stx subtyping PCR results were available for 131 isolates and 121 of these had concordant results with the stx subtype derived from the WGS data. Of the 10 discordant results, non-specific primer binding during PCR amplification, due to the similarity of the stx2 subtype gene sequences was the most likely cause. The results of this study showed WGS provided a reliable and robust one-step process for characterization of STEC. Deriving the full serotype from WGS data in real time has enabled us to report a higher level of strain discrimination while stx subtyping provides data on the pathogenic potential of each isolate, enabling us to predict clinical outcome of each case and to monitor the emergence of hyper-virulent strains.

Evaluation of Molecular Methods for Serotyping Shigella flexneri.

Shigella flexneri can be phenotypically serotyped using antisera raised to type-specific somatic antigens and group factor antigens and genotypically serotyped using PCR targeting O-antigen synthesis or modification genes. The aim of this study was to evaluate a real-time PCR for serotyping S. flexneri and to use whole-genome sequencing (WGS) to investigate the phenotypic and genotypic serotype identifications. Of the 244 cultures tested retrospectively, 226 (92.6%) had concordant results between phenotypic serotyping and PCR. Seventy of the 244 isolates (including 15 of the 18 isolates where a serotype-PCR mismatch was identified) were whole-genome sequenced, and the serotype was derived from the genome. Discrepant results between the phenotypic and genotypic tests were attributed to insertions/deletions or point mutations identified in O-antigen synthesis or modification genes, rendering them dysfunctional; inconclusive serotyping results due to nonspecific cross-reactions; or novel genotypes. Phylogenetic analysis of the WGS data indicated that the serotype, regardless of whether it was phenotypically or genotypically determined, was a weak predictor of phylogenetic relationships between strains of S. flexneri WGS data provided both genome-derived serotyping, thus supporting backward compatibility with historical data and facilitating data exchange in the community, and more robust and discriminatory typing at the single-nucleotide-polymorphism level.

Draft genome sequences of the type strains of Shigella flexneri held at Public Health England: comparison of classical phenotypic and novel molecular assays with whole genome sequence.

BACKGROUND: Public Health England (PHE) holds a collection of Shigella flexneri Type strains isolated between 1949 and 1972 representing 15 established serotypes and one provisional type, E1037. In this study, the genomes of all 16 PHE Type strains were sequenced using the Illumina HiSeq platform. The relationship between core genome phylogeny and serotype was examined. RESULTS: The most common target gene for the detection of Shigella species in clinical PCR assays, ipaH, was detected in all genomes. The type-specific target genes were correctly identified in each genome sequence. In contrast to the S. flexneri in serotype 5 strain described by Sun et al. (2012), the two PHE serotype 5 Type strains possessed an additional oac gene and were differentiated by the presence (serotype 5b) or absence (serotype 5a) of gtrX. The somatic antigen structure and phylogenetic relationship were broadly congruent for strains expressing serotype specific antigens III, IV and V, but not for those expressing I and II. The whole genome phylogenies of the 15 isolates sequenced showed that the serotype 6 Type Strain was phylogenetically distinct from the other S. flexneri serotypes sequenced. The provisional serotype E1037 fell within the serotype 4 clade, being most closely related to the Serotype 4a Type Strain. CONCLUSIONS: The S. flexneri genome sequences were used to evaluate phylogenetic relationships between Type strains and validate genotypic and phenotypic assays. The analysis confirmed that the PHE S. flexneri Type strains are phenotypically and genotypically distinct. Novel variants will continue to be added to this archive.