Optimized methods for detecting Salmonella Typhi in the environment using validated field sampling, culture and confirmatory molecular approaches

Jonathan Rigby*, Ezzeddine Elmerhebi, Yohane Diness, Charity Mkwanda, Katalina Tonthola, Heather Galloway, Rory Miles, Marc Y.R. Henrion, Thomas Edwards, Jillian Gauld, Chisomo Msefula, Rob Johnston, Satheesh Nair, Nicholas Feasey, Nicola C. Elviss

*Corresponding author for this work

Research output: Contribution to journalArticlepeer-review

Abstract

Aims: This study evaluated detection methods for Salmonella Typhi (S. Typhi) in the environment, to establish a novel pathway from field sampling to isolation of viable organisms and molecular confirmation from complex environmental samples, thus enabling environmental surveillance of typhoid. Methods and Results: Multiple media were assessed using clinical isolates from the Public Health England's (PHE) Culture collection. The culture pathway selected consisted of a primary 2% bile broth and secondary Selenite F broth, followed by modified Chromogenic Agar for Salmonella Esterase (mCASE). A qPCR assay was adapted from a validated S. Typhi PCR panel for confirmation of isolates, with comparison to biochemical and serological tests showing good specificity. Sampling locations in Blantyre, Malawi were used to compare sampling methods. Viable S. Typhi were isolated from a mixture of trap and grab river water samples on six occasions. Conclusions: Culture of viable S. Typhi from environmental samples was possible using effective capture and culture techniques. Significance and impact of study: Whilst several studies have attempted to detect S. Typhi from the environment, this is the first successful attempt to isolate the organism from river water since the 1980s. Supplementing clinical data with environmental screening offers the potential for enhanced surveillance, which might inform interventions and assess vaccination programmes.

Original languageEnglish
JournalJournal of Applied Microbiology
DOIs
Publication statusAccepted/In press - 2021

Bibliographical note

Funding Information:
The authors would like to thank the following individuals for their support of this work. Project Field Team: Pamela Kamanga; Stephano Chanza. Marie Chattaway and Gastrointestinal Bacteria Reference Unit at PHE for the provision of strains. Myron Levine and Michael Sikorski. This research was funded in part, by Wellcome Asia and Africa Programme Grant 206545/Z/17/Z. For the purpose of open access, the author has applied a CC BY public copyright licence to any Author Accepted Manuscript version arising from this submission

Publisher Copyright:
© 2021 The Authors. Journal of Applied Microbiology published by John Wiley & Sons Ltd on behalf of Society for Applied Microbiology

Keywords

  • Identification
  • Malawi
  • Moore swabs
  • PCR (polymerase chain reaction)
  • bile broth
  • biofilm
  • biofilms
  • mCASE
  • river water
  • salmonella
  • selenite broth
  • typhoid
  • water

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