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

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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
Early online date24 Aug 2021
DOIs
Publication statusEarly online - 24 Aug 2021

Keywords

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

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