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A contemporary genomic snapshot of Salmonella Paratyphi A in Pakistan Open Access

Abstract

Salmonella enterica serovar Paratyphi A is a significant but under-characterised cause of enteric fever in South Asia. In Pakistan, where the typhoid conjugate vaccine has been introduced to combat S. Typhi, S. Paratyphi A remains a prominent cause of bacteraemia, raising concerns about shifts in disease burden and antimicrobial resistance (AMR). Here, we provide a comprehensive genomic and phylogenetic analysis of 354 S. Paratyphi A isolates collected from three provinces in Pakistan between 2017 and early 2022. Whole-genome sequencing revealed the dominance of genotypes 2.3.3 and 2.4.5, indicating a largely stable population structure over time, and the presence of widespread fluoroquinolone-associated gyrA mutations. Although multidrug resistance was not detected, we identified one isolate harbouring an acrB-R717Q mutation associated with azithromycin resistance. Plasmid and replicon analysis revealed low prevalence of extrachromosomal elements, including cryptic plasmids with unknown function. Phylogenetic placement of these isolates in a global context demonstrated close relatedness to contemporary South Asian organisms. Our findings establish a genomic baseline for S. Paratyphi A in Pakistan, essential for future surveillance, AMR monitoring, and evaluating the potential impact of forthcoming paratyphoid vaccines.

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Funding
This study was supported by the:
  • Wellcome Trust (Award 215515/Z/19/Z)
    • Principal Award Recipient: StephenBaker
  • Bill and Melinda Gates Foundation (Award INV-030857)
    • Principal Award Recipient: NotApplicable
© 2025 The Authors
  • This is an open-access article distributed under the terms of the Creative Commons Attribution License. This article was made open access via a Publish and Read agreement between the Microbiology Society and the corresponding author’s institution.
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A contemporary genomic snapshot of Salmonella Paratyphi A in Pakistan
M Gen 11, 001561 (2025); https://doi.org/10.1099/mgen.0.001561
/content/journal/mgen/10.1099/mgen.0.001561
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