Antimicrobial resistance (AMR) represents a significant global health challenge, exacerbated by the misuse of antibiotics and the horizontal transfer of resistance genes across bacterial pathogens. The role of environmental stressors, such as disinfectants, in modulating AMR evolution and horizontal gene transfer remains underexplored.
This study investigates how triclosan (TCS), a commonly used disinfectant, influences the evolution of AMR in ๐๐ญ๐ฆ๐ฃ๐ด๐ช๐ฆ๐ญ๐ญ๐ข ๐ฑ๐ฏ๐ฆ๐ถ๐ฎ๐ฐ๐ฏ๐ช๐ข๐ฆ. Specifically, we assess whether TCS resistance affects bacterial permissiveness to multidrug-resistant (MDR) plasmids and susceptibility to phage infections.
Methods:
Researchers employed a combination of experimental evolution, whole-genome sequencing, reverse genetic engineering, and transcriptomics to explore the effects of TCS on ๐๐ญ๐ฆ๐ฃ๐ด๐ช๐ฆ๐ญ๐ญ๐ข ๐ฑ๐ฏ๐ฆ๐ถ๐ฎ๐ฐ๐ฏ๐ช๐ข๐ฆ. A clinical strain, ๐๐ญ๐ฆ๐ฃ๐ด๐ช๐ฆ๐ญ๐ญ๐ข ๐ฑ๐ฏ๐ฆ๐ถ๐ฎ๐ฐ๐ฏ๐ช๐ข๐ฆ Kp85, was exposed to incrementally increasing concentrations of TCS over 11 days. Resistant mutants (TRMs) were isolated and analyzed to identify genetic mutations, transcriptional changes, and alterations in antibiotic resistance profiles. They also assessed the permissiveness of these TRMs to MDR plasmids and their susceptibility to phages.
Key Findings:
TCS Resistance and Genetic Mutations:
- TCS exposure selected for ๐๐ญ๐ฆ๐ฃ๐ด๐ช๐ฆ๐ญ๐ญ๐ข ๐ฑ๐ฏ๐ฆ๐ถ๐ฎ๐ฐ๐ฏ๐ช๐ข๐ฆ mutants resistant to TCS and various clinical antibiotics, such as colistin, ciprofloxacin, and fosfomycin.
- Parallel mutations were observed in nsrR and ndh genes in TCS-resistant mutants, with additional mutations in genes like fabI (A21T), rppH, and intergenic regions.
- Transcriptomic analysis revealed altered expression of TCS and antibiotic target genes, indicating transcriptional rewiring possibly driven by genetic or epigenetic mechanisms.
Cross-Resistance and Antibiotic Resistance Genes:
- Increased expression of fabI, upregulation of the oqxB-like efflux pump, and changes in fosA and mgrB gene expression were linked to cross-resistance between TCS and antibiotics.
- The downregulation of mgrB and upregulation of oqxB-like and fosA5 genes contributed to the observed antibiotic resistance.
Permissiveness to MDR Plasmids:
- TCS-resistant ๐๐ญ๐ฆ๐ฃ๐ด๐ช๐ฆ๐ญ๐ญ๐ข ๐ฑ๐ฏ๐ฆ๐ถ๐ฎ๐ฐ๐ฏ๐ช๐ข๐ฆ mutants exhibited increased permissiveness to several MDR plasmids in the absence of TCS.
- This increased permissiveness was associated with the downregulation of bacterial defense systems, including type I-E CRISPR-Cas, toxin-antitoxin systems, and restriction-modification systems.
- The nsrR gene deletion specifically increased conjugation rates, suggesting a key role in enhancing bacterial permissiveness to plasmid DNA.
Susceptibility to Phage Infections:
- TCS-resistant mutants showed increased susceptibility to various ๐๐ญ๐ฆ๐ฃ๐ด๐ช๐ฆ๐ญ๐ญ๐ข-specific lytic phages.
- The deletion of nsrR enhanced susceptibility to phages by downregulating bacterial defense systems and altering membrane potential and reactive oxygen species (ROS) response.
Evolutionary Trade-offs:
- The evolution of TCS resistance in ๐๐ญ๐ฆ๐ฃ๐ด๐ช๐ฆ๐ญ๐ญ๐ข ๐ฑ๐ฏ๐ฆ๐ถ๐ฎ๐ฐ๐ฏ๐ช๐ข๐ฆ created a trade-off: while it increased resistance to antibiotics and MDR plasmid acquisition, it also heightened susceptibility to phage infections.
- This trade-off opens potential avenues for phage therapy to treat antibiotic-resistant ๐๐ญ๐ฆ๐ฃ๐ด๐ช๐ฆ๐ญ๐ญ๐ข ๐ฑ๐ฏ๐ฆ๐ถ๐ฎ๐ฐ๐ฏ๐ช๐ข๐ฆ infections, exploiting the increased phage susceptibility in TCS-resistant strains.
This study demonstrates that TCS exposure not only selects for TCS and antibiotic-resistant ๐๐ญ๐ฆ๐ฃ๐ด๐ช๐ฆ๐ญ๐ญ๐ข ๐ฑ๐ฏ๐ฆ๐ถ๐ฎ๐ฐ๐ฏ๐ช๐ข๐ฆ mutants but also enhances their permissiveness to MDR plasmids while increasing their susceptibility to phage infections.
The findings highlight the dual impact of TCS on bacterial resistance mechanisms and suggest potential therapeutic strategies using phages to combat antibiotic/TCS-resistant infections. Further research is necessary to fully understand the molecular mechanisms behind these adaptations and to develop effective interventions to curb the spread of AMR.
Link to the study : https://tinyurl.com/5edcswee
The proposed mechanisms underlying increased antimicrobial resistance to triclosan and clinical antibiotics and increasedย K.ย pneumoniae permissiveness to multidrug-resistant plasmids and susceptibility to phage infections.