Carriage of type II toxin-antitoxin systems by the growing group of IncX plasmids

Area of Science:

• Microbiology
• Genetics
• Molecular Biology

Background:

• Antibiotic resistance (AbR) is a global health emergency, with plasmids playing a key role in its spread.
• IncX plasmids, previously underestimated, are increasingly recognized for transmitting resistance to critical last-line antibiotics like carbapenems and colistin.
• Toxin-antitoxin (TA) systems are vital for the stable maintenance of antibiotic resistance plasmids in bacterial populations.

Purpose of the Study:

• To provide an updated overview of the IncX plasmid family.
• To conduct an in silico analysis of type II toxin-antitoxin (TA) systems within sequenced IncX plasmids.
• To characterize the diversity and distribution of TA systems across different IncX subgroups.

Main Methods:

• In silico analysis of 153 completely sequenced IncX plasmids from public databases.
• Identification and classification of type II toxin-antitoxin systems.
• Comparative analysis of TA system distribution across IncX subgroups (IncX1-IncX6).

Main Results:

• IncX1, IncX3, and IncX4 subgroups harbor the most numerous type II TA systems.
• RelE/ParE superfamily toxins are abundant in IncX1 and IncX4 plasmids, often paired with various antitoxins.
• The HicBA system is predominantly found in IncX4 plasmids; CcdB/MazF, PIN-like, and GNAT toxins are also identified, with multi-TA system plasmids being common.

Conclusions:

• IncX plasmids are significant reservoirs of diverse type II toxin-antitoxin systems.
• The characterization of TA systems in IncX plasmids deepens our understanding of their stable maintenance and role in antibiotic resistance.
• This study provides a comprehensive update on type II TA systems within the IncX plasmid family, highlighting their importance in bacterial genetics and the antibiotic resistance crisis.