Comparative Sequence Analysis of Multidrug-Resistant IncA/C Plasmids from Salmonella enterica

Area of Science:

• Microbiology
• Genomics
• Molecular Biology

Background:

• Multidrug resistance (MDR) in foodborne pathogens like Salmonella poses significant threats to human and veterinary health.
• Understanding MDR determinants encoded on mobile genetic elements, such as plasmids, is crucial for combating resistance.
• Previous studies were limited by the difficulty in obtaining closed plasmid genomes for comparative analysis.

Purpose of the Study:

• To develop and demonstrate an efficient protocol for isolating, sequencing, and closing IncA/C plasmids from Salmonella.
• To analyze the genetic makeup and evolutionary relationships of MDR plasmids in Salmonella.
• To provide insights into the evolution of antimicrobial resistance in agricultural settings.

Main Methods:

• Utilized single molecule real-time (SMRT) sequencing on a Pacific Biosciences (Pacbio) RS II Sequencer.
• Employed a modified mini preparation and Qiagen Large-Construct kit for plasmid DNA recovery.
• Sequenced six Salmonella enterica isolates from poultry exhibiting MDR-Ampc resistance profiles.

Main Results:

• Successfully obtained and closed six IncA/C plasmids, ranging from 104 to 191 kb.
• Identified a stable, conserved plasmid backbone with 98 core genes, showing minimal variation.
• Detected antimicrobial resistance genes, including those for quaternary ammonium compounds and mercury.
• Comparative analysis with existing IncA/C plasmids revealed evolutionary patterns of antimicrobial resistance.

Conclusions:

• The developed protocol enables efficient sequencing and closing of high-molecular-weight, low-copy-number plasmids.
• IncA/C plasmids possess a conserved backbone that facilitates the spread of antimicrobial resistance genes.
• This research offers valuable genetic and phylogenetic insights into MDR evolution in diverse Salmonella serotypes from agricultural sources.