Abstract
BackgroundClass 1 integrons contain genetic elements for site-specific recombination, capture and mobilization of resistance genes. Studies investigating the prevalence, distribution and types of integron located resistance genes are important for surveillance of antimicrobial resistance and to understand resistance development at the molecular level.MethodsWe determined the prevalence and genetic content of class 1 integrons in Enterobacteriaceae (strain collection 1, n = 192) and E. coli (strain collection 2, n = 53) from bloodstream infections in patients from six Norwegian hospitals by molecular techniques. Class 1 integrons were also characterized in 54 randomly selected multiresistant E. coli isolates from gastrointestinal human infections (strain collection 3).ResultsClass 1 integrons were present in 10.9% of the Enterobacteriaceae blood culture isolates of collection 1, all but one (S. Typhi) being E. coli. Data indicated variations in class 1 integron prevalence between hospitals. Class 1 integrons were present in 37% and 34% of the resistant blood culture isolates (collection 1 and 2, respectively) and in 42% of the resistant gastrointestinal E. coli. We detected a total of 10 distinct integron cassette PCR amplicons that varied in size between 0.15 kb and 2.2 kb and contained between zero and three resistance genes. Cassettes encoding resistance to trimethoprim and aminoglycosides were most common. We identified and characterized a novel plasmid-located integron with a cassette-bound novel gene (linF) located downstream of an aadA2 gene cassette. The linF gene encoded a putative 273 aa lincosamide nucleotidyltransferase resistance protein and conferred resistance to lincomycin and clindamycin. The deduced LinF amino acid sequence displayed approximately 35% identity to the Enterococcus faecium and Enterococcus faecalis nucleotidyl transferases encoded by linB and linB'ConclusionsThe present study demonstrated an overall low and stable prevalence of class 1 integron gene cassettes in clinical Enterobacteriaceae and E. coli isolates in Norway. Characterization of the novel lincosamide resistance gene extends the growing list of class 1 integron gene cassettes that confer resistance to an increasing number of antibiotics.
Highlights
Class 1 integrons contain genetic elements for site-specific recombination, capture and mobilization of resistance genes
Five distinct integron classes have been found [2] with more than 60 different antibiotic resistance genes identified within gene cassettes either alone or in combination [3,4]
The 3' conserved segment usually contains the truncated qacE gene encoding low level resistance to disinfectants based on quaternary ammonium compounds, the sul1 gene encoding sulfonamide resistance and an open reading frame (ORF5) of unknown function [4,10]
Summary
Class 1 integrons contain genetic elements for site-specific recombination, capture and mobilization of resistance genes. Distribution and types of integron located resistance genes are important for surveillance of antimicrobial resistance and to understand resistance development at the molecular level. In class 1 integrons, dominating in clinical Enterobacteriaceae isolates [5,6,7], the 5' conserved region contains essential elements for insertion and mobilization of gene cassettes: the intI1 gene encoding the integrase which catalyzes site-specific recombination of adjacent gene cassettes; attI, the specific gene cassette insertion site, and Pc, a promoter common for transcription of cassette resistance genes [8,9]. Few studies exist on the prevalence and distribution of integrons from distinct clinical settings (e.g. blood culture isolates and gastrointestinal E. coli). A narrow spectrum of different gene cassette combinations was observed, we identified and characterized a new plasmid-born class 1 integron located in a blood culture E. coli isolate. The integron contained two cassettes including a novel gene, linF that encoded a putative lincosamide nucleotidyl transferase that conferred resistance to the lincosamides clindamycin and lincomycin
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