Polymorphism of gene cassette promoter variants of class 1 integron harbored in S. Choleraesuis and Typhimurium isolated from Taiwan

Abstract

Integrons, mobile genetic units, capture and incorporate antibiotic resistance gene cassette by site-specific recombination. Class 1 integrons are widespread and associated with dispersion of antibiotic resistance among Gram-negative bacteria. The expression of gene cassette in Class 1 can vary, based on the Pc promoter but seldom from another promoter hiding downstream of Pc, called P2. To probe distribution and prevalence of gene cassette promoter variants, we analyzed 169 S. Choleraesuis and 191 S. Typhimurium isolates from humans and animals, finding 95.27% occurrence of integrin among S. Choleraesuis, 83.25% among S. Typhimurium. PCR-RFLP analysis identified four promoters (PcS+P2, PcWTGN-10+P2, PcH1+P2, and PcWTGN-10+P2-GGG) in said integron-positive isolates major types in S. Choleraesuis and S. Typhimurium were PcS+P2 and PcWTGN-10+P2, respectively. Likewise, β-galactosidase assay rated promoter strength of variants by transcriptional fusion constructs to show extended-10 promoter (TGn/-10 promoter) in Pc and three-nucleotide insertion (GGG) between-35 and-10 region of P2 improving promoter strength of gene cassette.