Composite integron array generated by insertion of an ORF341-type integron within a Tn21-like element

Area of Science:

• Microbiology
• Genetics
• Molecular Biology

Background:

• Class 1 integrons are mobile genetic elements that contribute to antimicrobial resistance.
• IncFI plasmids are prevalent in Salmonella enterica serotype Typhimurium, a significant foodborne pathogen.
• Previous studies identified two class 1 integrons, In-t1 and In-t2, within IncFI plasmids of S. Typhimurium.

Purpose of the Study:

• To investigate the physical linkage and structural characteristics of In-t1 and In-t2 integrons in IncFI plasmids.
• To identify novel genes and genetic elements associated with these integrons.
• To trace the evolutionary history and acquisition events of these integrons in Salmonella.

Main Methods:

• Molecular analysis of IncFI plasmids from S. Typhimurium.
• DNA sequencing and structural comparison of integrons and associated transposons.
• Retrospective analysis of historical plasmid data.

Main Results:

• In-t1 and In-t2 integrons are physically linked in a head-to-tail configuration on IncFI plasmids.
• In-t1 contains an extended ORF341 (ORF341E) and a novel trimethoprim resistance gene, dfrA18.
• In-t1 insertion into Tn1935, a Tn21-related transposon, occurred after the assembly of Tn1935 and within the 5'-conserved segment of In-t2.
• In-t2 has been conserved in IncFI plasmids over time.

Conclusions:

• In-t1 represents a novel family of class 1 integrons characterized by the ORF341E sequence.
• The acquisition of In-t1 by IncFI plasmids is a relatively recent event.
• The findings provide insights into the evolution and dissemination of antimicrobial resistance genes in Salmonella.