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.
Highlights
Salmonellosis ranks among the most common bacterial infections worldwide [1]
The USA diagnoses over 4 million cases of Salmonella infection per annum [6], about 500 fatal [2,7]
Multidrug resistant genes transmitted between human and animal pathogens [12] mean mobile genetic elements playing a key role in dispersion of drug resistance among bacterial population [13-16]
Summary
Salmonellosis ranks among the most common bacterial infections worldwide [1]. Until 2004, over 2,500 Salmonella serotypes were identified [3] Among these serovars, Salmonella enterica serovar Choleraesuis and Typhimurium are common non-typhoidal serotypes that pose global concern [4,5]. While mild and self-limited in adults, salmonellosis can require drugs, especially antibiotics, to treat infant, elderly, or immunocomprised patients [8]. Studies show ever more multidrug resistance by Salmonella, causing serious public health hazards [5,9,10]. Such mechanisms entail obtaining genes or point mutation in genomes [11], resistance dispersed by [1] clonal expansion of drug-resistant strains or [2] horizontal transfer of determinants. Multidrug resistant genes transmitted between human and animal pathogens [12] mean mobile genetic elements playing a key role in dispersion of drug resistance among bacterial population [13-16]
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