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Review 1: "Detection of Salmonella Typhi and blaCTX-M Genes in Drinking Water, Wastewater, and Environmental Biofilms in Sindh Province, Pakistan"

Overall, both the reviewers find that this study builds on previous work on the role of biofilm as a pathogen reservoir in urban water systems. However, they expressed concerns about the strength of evidence to support its claims.

Published onMay 23, 2024
Review 1: "Detection of Salmonella Typhi and blaCTX-M Genes in Drinking Water, Wastewater, and Environmental Biofilms in Sindh Province, Pakistan"
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key-enterThis Pub is a Review of
Detection of Salmonella Typhi and blaCTX-M Genes in Drinking Water, Wastewater, and Environmental Biofilms in Sindh Province, Pakistan
Detection of Salmonella Typhi and blaCTX-M Genes in Drinking Water, Wastewater, and Environmental Biofilms in Sindh Province, Pakistan
Description

Abstract Typhoid fever poses a significant public health risk, particularly in low- and middle-income countries where access to clean water and improved sanitation may be limited. In Pakistan, this risk is especially serious given the emergence of an extensively drug-resistant (XDR) Salmonella Typhi strain, a strain attributed to S. Typhi acquisition of the blaCTX-M-15 gene. The now-dominant XDR S. Typhi strain, non-XDR S. Typhi, and blaCTX-M genes are readily disseminated via drinking water and wastewater in Pakistan and may also be present in biofilms associated with these environmental sources. This study investigates the presence of S. Typhi and blaCTX-M genes within these environmental compartments. Drinking water (n=35) or wastewater samples (n=35) and samples of their associated biofilms were collected from Karachi and Hyderabad, Pakistan. Samples were tested by PCR for S. Typhi and blaCTX-M group 1 genes as a proxy for blaCTX-M-15. Heterotrophic plate counts (HPC) were conducted to assess microbial load. S. Typhi was detected by PCR in one bulk wastewater sample and one drinking water biofilm. BlaCTX-M group 1 genes were detected in all sample types and were detected more frequently in bulk wastewater (n=13/35) than in drinking water (n=2/35) and more frequently overall in biofilm samples (n=22/70) versus bulk water (n=15/70). Detection of blaCTX-M in biofilm was not significantly associated with detection in the associated bulk water sample. This study marks the first detection of S. Typhi in drinking water biofilms and the first report of blaCTX-M genes in environmental biofilms in Pakistan. Environmental biofilms, particularly in drinking water systems, may serve as reservoirs for human exposure to S. Typhi and drug resistance genes. This study underscores the importance of expanding surveillance strategies to include biofilm sampling, providing valuable insights into pathogen dissemination in water systems, and informing targeted public health interventions to prevent waterborne diseases.

RR:C19 Evidence Scale rating by reviewer:

  • Potentially informative. The main claims made are not strongly justified by the methods and data, but may yield some insight. The results and conclusions of the study may resemble those from the hypothetical ideal study, but there is substantial room for doubt. Decision-makers should consider this evidence only with a thorough understanding of its weaknesses, alongside other evidence and theory. Decision-makers should not consider this actionable, unless the weaknesses are clearly understood and there is other theory and evidence to further support it.

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Review: The primary objective of this study was to determine if S. Typhi could be detected in drinking water, wastewater, or their associated biofilms in urban areas in Sindh Province. This study underscores the importance of expanding surveillance strategies to include biofilm sampling.

This study collected 35 drinking water, 35 wastewater, and 70 biofilm samples (from the same sites where the water samples were collected) in urban areas in Pakistan. The authors analyzed genes for Salmonella Typhi (Typhoid fever-causing agent) and blaCTX-M group 1 gene (multidrug resistance gene). They detected Salmonella Typhi in 2 out of 140 samples, and blaCTX-M group 1 gene in 37 out of 140 samples. Two major conclusions were drawn. Firstly, the authors emphasize that the blaCTX-M group 1 gene is prevalent in the water system, which is well supported by their results. Secondly, they suggest that biofilm should be included in surveillance due to the higher probability of detecting the blaCTX-M group 1 gene. The second conclusion could have been strengthened with more data, such as different sampling campaigns and controlled sampling procedures to compare water and biofilm. In terms of data quality, the authors could have provided more information and control experiments, such as details about the Limit of Detection (LOD) and adherence to the MIQE guidelines for PCR analysis. Overall, while the manuscript is well-organized and well-written, the lack of experimental data results in less novel and meaningful conclusions.

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