Multiplex PCR assay to detect high risk lineages of Salmonella Typhi and Paratyphi A

Enteric fever infections remain a significant public health issue, with up to 20 million infections per year. Increasing rates of antibiotic resistant strains have rendered many first-line antibiotics potentially ineffective. Genotype 4.3.1 (H58) is the main circulating lineage of S. Typhi in many South Asian countries and is associated with high levels of antibiotic resistance. The emergence and spread of extensively drug resistant (XDR) typhoid strains has increased the need for a rapid molecular test to identify and track these high-risk lineages for surveillance and vaccine prioritisation. Current methods require samples to be cultured for several days, followed by DNA extraction and sequencing to determine the specific lineage. We designed and evaluated the performance of a new multiplex PCR assay, targeting S. Paratyphi A as well as the H58 and XDR lineages of S. Typhi on a collection of bacterial strains. Our assay was 100% specific for the identification of lineage specific S. Typhi and S. Paratyphi A, when tested with a mix of non-Typhi Salmonella and non-Salmonella strains. With additional testing on clinical and environmental samples, this assay will allow rapid lineage level detection of typhoid of clinical significance, at a significantly lower cost to whole-genome sequencing. To our knowledge, this is the first report of a SNP-based multiplex PCR assay for the detection of lineage specific serovars of Salmonella Typhi

Hybrid Plasmids Encoding Antimicrobial Resistance and Virulence Traits Among Hypervirulent Klebsiella pneumoniae ST2096 in India.

BACKGROUND: Hypervirulent variants of Klebsiella pneumoniae (HvKp) were typically associated with a broadly antimicrobial susceptible clone of sequence type (ST) 23 at the time of its emergence. Concerningly, HvKp is now also emerging within multidrug-resistant (MDR) clones, including ST11, ST15, and ST147. MDR-HvKp either carry both the virulence and resistance plasmids or carry a large hybrid plasmid coding for both virulence and resistance determinants. Here, we aimed to genetically characterize a collection of MDR-HvKp ST2096 isolates haboring hybrid plasmids carrying both antimicrobial resistance (AMR) and virulence genes. METHODS: Nine K. pneumoniae ST2096 isolated over 1 year from the blood sample of hospitalized patients in southern India that were MDR and suspected to be HvKp were selected. All nine isolates were subjected to short-read whole-genome sequencing; a subset (n = 4) was additionally subjected to long-read sequencing to obtain complete genomes for characterization. Mucoviscosity assay was also performed for phenotypic assessment. RESULTS: Among the nine isolates, seven were carbapenem-resistant, two of which carried blaNDM-5 on an IncFII plasmid and five carried blaOXA-232 on a ColKP3 plasmid. The organisms were confirmed as HvKp, with characteristic virulence genes (rmpA2, iutA, and iucABCD) carried on a large (~320 kbp) IncFIB-IncHI1B co-integrate. This hybrid plasmid also carried the aadA2, armA, blaOXA-1, msrE, mphE, sul1, and dfrA14 AMR genes in addition to the heavy-metal resistance genes. The hybrid plasmid showed about 60% similarity to the IncHI1B virulence plasmid of K. pneumoniae SGH10 and ~70% sequence identity with the first identified IncHI1B pNDM-MAR plasmid. Notably, the hybrid plasmid carried its type IV-A3 CRISPR-Cas system which harbored spacer regions against traL of IncF plasmids, thereby preventing their acquisition. CONCLUSION: The convergence of virulence and AMR is clinically concerning in K. pneumoniae. Our data highlight the role of hybrid plasmids carrying both AMR and virulence genes in K. pneumoniae ST2096, suggesting that MDR-HvKp is not confined to selected clones; we highlight the continued emergence of such genotypes across the species. The convergence is occurring globally amidst several clones and is of great concern to public health

Multiplex PCR assay to detect high risk lineages of Salmonella Typhi and Paratyphi A.

Funder: National Institute for Health Research (NIHR)Funder: Bill and Melinda Gates FoundationEnteric fever infections remain a significant public health issue, with up to 20 million infections per year. Increasing rates of antibiotic resistant strains have rendered many first-line antibiotics potentially ineffective. Genotype 4.3.1 (H58) is the main circulating lineage of S. Typhi in many South Asian countries and is associated with high levels of antibiotic resistance. The emergence and spread of extensively drug resistant (XDR) typhoid strains has increased the need for a rapid molecular test to identify and track these high-risk lineages for surveillance and vaccine prioritisation. Current methods require samples to be cultured for several days, followed by DNA extraction and sequencing to determine the specific lineage. We designed and evaluated the performance of a new multiplex PCR assay, targeting S. Paratyphi A as well as the H58 and XDR lineages of S. Typhi on a collection of bacterial strains. Our assay was 100% specific for the identification of lineage specific S. Typhi and S. Paratyphi A, when tested with a mix of non-Typhi Salmonella and non-Salmonella strains. With additional testing on clinical and environmental samples, this assay will allow rapid lineage level detection of typhoid of clinical significance, at a significantly lower cost to whole-genome sequencing. To our knowledge, this is the first report of a SNP-based multiplex PCR assay for the detection of lineage specific serovars of Salmonella Typhi

Genomic analysis unveils genome degradation events and gene flux in the emergence and persistence of S. Paratyphi A lineages.

Acknowledgements: We thank Prof. Nicholas Grassly, Imperial College London, for assistance with study design and research proposal development. We gratefully acknowledge Dr. Arif M. Tanmoy, Dr. Senjuti Saha and Dr. Yogesh Hooda (CHRF, Dhaka, Bangladesh) for help with the genotyping analysis. We acknowledge Dr. Duncan Steele, Ms. Megan Carey & Dr. Supriya Kumar, Bill & Melinda Gates Foundation for their technical support throughout the study on behalf of SEFI consortium. We thank all the lab members involved in SEFI reference lab activities, especially Dr. Anushree Amladi, Ms. Baby Abirami S, Ms. Dhanabhagyam K, Ms. Beebi E, Ms. Suganya S, Ms. Udaya and Mr. Ayyanraj N, CMC Vellore implicated in phenotypic testing and stock culture maintenance. We would also like to thank all the members of SEFI consortium, Wellcome Trust Research Laboratory, CMC Vellore and core sequencing teams at the Wellcome Trust Sanger Institute for their contribution to genome sequencing. The authors thank Ms Catherine Trueman (Clinical Pharmacist, CMC Vellore) for helping with language editing.Paratyphoid fever caused by S. Paratyphi A is endemic in parts of South Asia and Southeast Asia. The proportion of enteric fever cases caused by S. Paratyphi A has substantially increased, yet only limited data is available on the population structure and genetic diversity of this serovar. We examined the phylogenetic distribution and evolutionary trajectory of S. Paratyphi A isolates collected as part of the Indian enteric fever surveillance study "Surveillance of Enteric Fever in India (SEFI)." In the study period (2017-2020), S. Paratyphi A comprised 17.6% (441/2503) of total enteric fever cases in India, with the isolates highly susceptible to all the major antibiotics used for treatment except fluoroquinolones. Phylogenetic analysis clustered the global S. Paratyphi A collection into seven lineages (A-G), and the present study isolates were distributed in lineages A, C and F. Our analysis highlights that the genome degradation events and gene acquisitions or losses are key molecular events in the evolution of new S. Paratyphi A lineages/sub-lineages. A total of 10 hypothetically disrupted coding sequences (HDCS) or pseudogenes-forming mutations possibly associated with the emergence of lineages were identified. The pan-genome analysis identified the insertion of P2/PSP3 phage and acquisition of IncX1 plasmid during the selection in 2.3.2/2.3.3 and 1.2.2 genotypes, respectively. We have identified six characteristic missense mutations associated with lipopolysaccharide (LPS) biosynthesis genes of S. Paratyphi A, however, these mutations confer only a low structural impact and possibly have minimal impact on vaccine effectiveness. Since S. Paratyphi A is human-restricted, high levels of genetic drift are not expected unless these bacteria transmit to naive hosts. However, public-health investigation and monitoring by means of genomic surveillance would be constantly needed to avoid S. Paratyphi A serovar becoming a public health threat similar to the S. Typhi of today

List of functional gene inactivation mutations identified between phylogenetic lineages.

List of functional gene inactivation mutations identified between phylogenetic lineages.</p

Antimicrobial susceptibility profile of <i>S</i>. Paratyphi A tested in the present study.

Antimicrobial susceptibility profile of S. Paratyphi A tested in the present study.</p

Distribution of <i>S</i>. Typhi and <i>S</i>. Paratyphi A isolates collected across the participating sites of the SEFI network.

Distribution of S. Typhi and S. Paratyphi A isolates collected across the participating sites of the SEFI network.</p