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Published on: January 27, 2021
Ciprofloxacin induced antibiotic resistance in Salmonella Typhimurium mutants and genome analysis
Aarti S Kakatkar1, Anubrata Das2, Ravindranath Shashidhar3,4
1Food Technology Division, Bhabha Atomic Research Centre, Trombay, Mumbai, 400085, India.
Abstract:
Antibiotic resistance of Salmonella species is well reported. Ciprofloxacin is the frontline antibiotic for salmonellosis. The repeated exposure to ciprofloxacin leads to resistant strains. After 20 cycles of antibiotic exposure, resistant bacterial clones were evaluated. The colony size of the mutants was small and had an extended lag phase compared to parent strain. The whole genome sequencing showed 40,513 mutations across the genome. Small percentage (5.2%) of mutations was non-synonymous. Four-fold more transitions were observed than transversions. Ratio of < 1 transition vs transversion showed a positive selection for antibiotic resistant trait. Mutation distribution across the genome was uniform. The native plasmid was an exception and 2 mutations were observed on 90 kb plasmid. The important genes like dnaE, gyrA, iroC, metH and rpoB involved in antibiotic resistance had point mutations. The genome analysis revealed most of the metabolic pathways were affected.
Insights
Repeated ciprofloxacin exposure created Salmonella mutants with small colonies and longer lag times. Genome analysis revealed numerous mutations, including in key antibiotic resistance genes, indicating positive selection for resistance.
Area of Science:
- Microbiology
- Genomics
- Molecular Biology
Background:
- Antibiotic resistance in Salmonella species is a significant global health concern.
- Ciprofloxacin is a primary treatment for salmonellosis, but its overuse drives resistance.
- Understanding the genetic basis of resistance is crucial for developing effective treatments.
Purpose of the Study:
- To investigate the genomic changes in Salmonella following prolonged ciprofloxacin exposure.
- To identify specific mutations associated with acquired ciprofloxacin resistance.
- To analyze the impact of these mutations on bacterial physiology and fitness.
Main Methods:
- Salmonella cultures were subjected to 20 cycles of increasing ciprofloxacin concentrations.
- Phenotypic characteristics of resistant mutants (colony size, lag phase) were compared to the parent strain.
- Whole genome sequencing was performed to identify and analyze mutations.
- Bioinformatic analyses were conducted to assess mutation distribution, types, and impact on genes and pathways.
Main Results:
- Ciprofloxacin-resistant Salmonella mutants exhibited smaller colony sizes and extended lag phases.
- Whole genome sequencing identified 40,513 mutations, with a majority being synonymous.
- A higher ratio of transitions to transversions and a transition/transversion ratio < 1 suggested positive selection for resistance.
- Mutations were uniformly distributed, with the exception of the native plasmid.
- Key genes involved in antibiotic resistance (dnaE, gyrA, iroC, metH, rpoB) harbored point mutations.
- Most metabolic pathways were found to be affected in the resistant strains.
Conclusions:
- Prolonged ciprofloxacin exposure induces significant genomic alterations in Salmonella, leading to resistance.
- The observed mutation patterns indicate strong positive selection for the antibiotic-resistant trait.
- Acquired resistance impacts bacterial fitness and affects multiple metabolic pathways.
- These findings highlight the rapid evolution of antibiotic resistance in Salmonella and its genetic underpinnings.
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