Multiple adaptive routes of Salmonella enterica Typhimurium to biocide and antibiotic exposure.

Tânia Curiao,José Luis Martinez,Stephen L Leib,Marco R Oggioni,Teresa M Coque,Denis Grandgirard,Fernando Baquero,Ricardo León-Sampedro,Carlo Viti,Emmanuela Marchi

doi:10.1186/s12864-016-2778-z

Abstract

BackgroundBiocides and antibiotics are used to eradicate or prevent the growth of microbial species on surfaces (occasionally on catheters), or infected sites, either in combination or sequentially, raising concerns about the development of co-resistance to both antimicrobial types. The effect of such compounds on Salmonella enterica, a major food-borne and zoonotic pathogen, has been analysed in different studies, but only few works evaluated its biological cost, and the overall effects at the genomic and transcriptomic levels associated with diverse phenotypes resulting from biocide exposure, which was the aim of this work.ResultsExposure to triclosan, clorhexidine, benzalkonium, (but not to hypochlorite) resulted in mutants with different phenotypes to a wide range of antimicrobials even unrelated to the selective agent. Most biocide-resistant mutants showed increased susceptibility to compounds acting on the cell wall (β-lactams) or the cell membranes (poly-L-lysine, polymyxin B, colistin or toxic anions). Mutations (SNPs) were found in three intergenic regions and nine genes, which have a role in energy production, amino acids, carbohydrates or lipids metabolism, some of them involved in membrane transport and pathogenicity. Comparative transcriptomics of biocide-resistant mutants showed over-expression of genes encoding efflux pumps (sugE), ribosomal and transcription-related proteins, cold-shock response (cpeE) and enzymes of microaerobic metabolism including those of the phosphotransferase system. Mainly ribosomal, metabolic and pathogenicity-related genes had affected expression in both in vitro-selected biocide mutants and field Salmonella isolates with reduced biocide susceptibility.ConclusionsMultiple pathways can be involved in the adaptation of Salmonella to biocides, mainly related with global stress, or involving metabolic and membrane alterations, and eventually causing “collateral sensitivity” to other antimicrobials. These changes might impact the bacterial-environment interaction, imposing significant bacterial fitness costs which may reduce the chances of fixation and spread of biocide resistant mutants.Electronic supplementary materialThe online version of this article (doi:10.1186/s12864-016-2778-z) contains supplementary material, which is available to authorized users.

Highlights

Biocides and antibiotics are used to eradicate or prevent the growth of microbial species on surfaces, or infected sites, either in combination or sequentially, raising concerns about the development of co-resistance to both antimicrobial types
Exposure to biocides or antibiotics yield mutants with different susceptibility to biocides and antimicrobials Table 1 shows the diversity of mutants exhibiting phenotypes obtained (4 TRIR/BKCR/CHXR, 1 TRIR/BKCR, 4 BKCR/CHXR/TRIHS, 2 BKCR, 2 TRIHS and 1 TRIHS/ CHXHS)
Some mutants with increased minimal inhibitory concentrations (MICs) to biocides were obtained without previous exposure to any antimicrobial but using selective plates supplemented with TRI, BKC or CHX

Summary

Introduction

Biocides and antibiotics are used to eradicate or prevent the growth of microbial species on surfaces (occasionally on catheters), or infected sites, either in combination or sequentially, raising concerns about the development of co-resistance to both antimicrobial types The effect of such compounds on Salmonella enterica, a major food-borne and zoonotic pathogen, has been analysed in different studies, but only few works evaluated its biological cost, and the overall effects at the genomic and transcriptomic levels associated with diverse phenotypes resulting from biocide exposure, which was the aim of this work. Few studies provided comprehensive information about the genomic and transcriptomic changes of mutants selected after exposure to different biocides and antibiotics, which can be used either coincidentally or sequentially in the clinical practice and in the food industry [9, 22,23,24]

Objectives

Methods

Results

Discussion

Conclusion