Integron Analysis and Genetic Mapping of Antimicrobial Resistance Genes in Salmonella enterica serotype Typhimurium
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Antimicrobial resistance determinants may be transferred among bacteria via mobile genetic elements including plasmids, transposons, and the more recently explored integrons ( 1 ). Integrons are naturally occurring genetic elements found as part of the Tn 21 transposon family or located on various broad host-range plasmids ( 2 ). The fundamental integron structure consists of a 5′-conserved segment (5′-CS) of 1.4-kbp and a 2-kbp 3′-CS ( 3 ). Between these conserved regions are DNA sequences of variable length and molecular complexity. These intervening sequences are known as gene cassettes , and several have now been characterized (Fig. 1 ). Acquisition and dissemination of these genes located within the integron structure, results in an increase in antimicrobial resistance ( 4 ).
Fig.1. Schematic representation of a class 1 integron structure. Several gene cassettes (hatched box) have been found located between the 5′- and 3′-CS. Often, more than one open reading frame (ORF) gene cassette can be found within the same integron, in the same orientation, and transcribed from a common promoter located proximal to the 5′-site of insertion.
