Multiple drug resistant (MDR) extra-intestinal pathogenic Escherichia coli (ExPEC)are frequently implicated as the causative agent of urinary tract infections (UTI) leading to increased mortality and treatment times. The role played by ExPEC ingested via contaminated food however is less clear. It is currently proposed that UTI may be caused by human ingestion of an ExPEC and subsequent urinary tract contamination by personal faecal matter. These bacteria are likely to possess complex resistance loci due to the antibiotic pressures imposed on the commensal gut bacteria of food animals.
Tn6026 is flanked by direct copies of IS26 andmediates resistance to ampicillin, sulfonamides, streptomycin, kanamycin and neomycin. It has been identified in enterohaemolytic (EHEC) and enteropathogenic (EPEC) E. coli in cattle in Australia. Preliminary data in our lab has identified Tn6029, a transposon related to Tn6026, in uropathogenic Escherichia coli (UPEC) isolates from a Sydney hospital.
To determine the frequency of these transposons in E. coli sourced from food-producing animals, 50 MDR commensal porcine E. coli isolates from a farm in NSW with a history of heavy kanamycin use were subjected to PCR screens using primers specific for regions of Tn6026 and Tn6029. Our analyses showed that at least one of these transposonswere present in 33/50 isolates (66%) that also carry class 1 integrons and Tn21 family mercury resistance transposons.
To determine if these IS26-flanked transposons are found in close proximity to class 1 integrons we applied a diagnostic PCR with a primer (L1) in the class 1 integrase gene intI1 and a primer in IS26 (JLD2). Our analysis identified an 848 bp amplicon encoding ∆intI1-dfrA5-24 bp 3´-CS-∆IS26 previously observed in MDR EHEC and EPEC strains circulating in bovine populations in NSW. These data suggest that the mobile element responsible for mobilizing this atypical class 1 integron is disseminated widely.