Prevalence and characterization of plasmids carrying sulfonamide resistance genes among Escherichia coli from pigs, pig carcasses and human

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Wu, Shuyu ; Dalsgaard, Anders ; Hammerum, Anette Marie ; Porsbo, Lone Jannok ; Jensen, Lars B. (2010)

<p>Abstract</p> <p>Background</p> <p>Sulfonamide resistance is very common in <it>Escherichia coli</it>. The aim of this study was to characterize plasmids carrying sulfonamide resistance genes (<it>sul1</it>, <it>sul2 </it>and <it>sul3</it>) in <it>E. coli </it>isolated from pigs and humans with a specific objective to assess the genetic diversity of plasmids involved in the mobility of <it>sul </it>genes.</p> <p>Methods</p> <p>A total of 501 <it>E. coli </it>isolates from pig feces, pig carcasses and human stools were tested for their susceptibility to selected antimicrobial. Multiplex PCR was conducted to detect the presence of three <it>sul </it>genes among the sulfonamide-resistant <it>E. coli </it>isolates. Fifty-seven sulfonamide-resistant <it>E. coli </it>were selected based on presence of <it>sul </it>resistance genes and subjected to conjugation and/or transformation experiments. S1 nuclease digestion followed by pulsed-field gel electrophoresis was used to visualize and determine the size of plasmids. Plasmids carrying <it>sul </it>genes were characterized by PCR-based replicon typing to allow a comparison of the types of <it>sul </it>genes, the reservoir and plasmid present.</p> <p>Results</p> <p>A total of 109/501 isolates exhibited sulfonamide resistance. The relative prevalences of s<it>ul </it>genes from the three reservoirs (pigs, pig carcasses and humans) were 65%, 45% and 12% for <it>sul2</it>, <it>sul1</it>, and <it>sul3</it>, respectively. Transfer of resistance through conjugation was observed in 42/57 isolates. Resistances to streptomycin, ampicillin and trimethoprim were co-transferred in most strains. Class 1 integrons were present in 80% of s<it>ul1</it>-carrying plasmids and 100% of <it>sul3</it>-carrying plasmids, but only in 5% of <it>sul2</it>-carrying plasmids. The <it>sul </it>plasmids ranged from 33 to 160-kb in size and belonged to nine different incompatibility (Inc) groups: FII, FIB, I1, FIA, B/O, FIC, N, HI1 and X1. IncFII was the dominant type in <it>sul2</it>-carrying plasmids (52%), while IncI1 was the most common type in <it>sul1 </it>and <it>sul3</it>-carrying plasmids (33% and 45%, respectively). Multireplicons were found associated with all three <it>sul </it>genes.</p> <p>Conclusions</p> <p><it>Sul </it>genes were distributed widely in <it>E. coli </it>isolated from pigs and humans with <it>sul2 </it>being most prevalent. <it>Sul</it>-carrying plasmids belonged to diverse replicon types, but most of detected plasmids were conjugative enabling horizontal transfer. IncFII seems to be the dominant replicon type in <it>sul2</it>-carrying plasmids from all three sources.</p>
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