IDENTIFICATION OF IS1356, A NEW INSERTION-SEQUENCE, AND ITS ASSOCIATION WITH IS402 IN EPIDEMIC STRAINS OF BURKHOLDERIA-CEPACIA INFECTING CYSTIC-FIBROSIS PATIENTS

Burkholderia cepacia is now recognized as an important opportunistic p athogen in cystic fibrosis (CF) and other compromised patients. Epidem icity among CF patients has been attributed to at least one particular ly infectious strain (strain ET12), and both genetic evidence and anec dotal evidence suggest that this strain, currently endemic in Ontario, and those causing an epidemic in the United Kingdom, are indeed the s ame. Our study was conducted to determine whether there was any associ ation between the presence of various insertion sequence (IS) elements , the cable pilin subunit gene (cblA), electrophoretic type (ET), and ribotype (RT) in a collection of 97 clinical and 2 environmental isola tes of B. cepacia. No apparent linkage was found for IS elements IS401 , IS402, IS406, IS407, and IS408 with ET or RT. The cblA target, said to be a marker for high infectivity, was detected in 100% (38 of 38) o f strains of B. cepacia ET12 and in a single strain of ET13 that diffe red in a single enzyme allele. A new IS, IS1356, identified during the investigation, was present in 71.7% of all isolates, and 50.7% of the se isolates harbored IS1356 as a hybrid IS element inserted into IS402 , IS1356 is 1,353 bp in length, and when it is inserted into IS402 it results in a 10-bp duplication at the site of insertion. IS1356 contai ns one major open reading frame of 1,260 bp coding for a putative tran sposase which has significant homology to ISRm3 in Rhizobium meliloti (59%) and to an undesignated IS element in Corynebacterium diphtheriae (49%). The IS402-IS1356 element was found exclusively in the epidemic strains from Ontario and the United Kingdom, being detected in 94.7% (36 of 38 isolates) of B. cepacia ET12 isolates. Of the two ET12 isola tes found to be devoid of the IS402-IS1356 element, both contained IS1 356 unassociated with IS402, one was temporally unrelated to the epide mic, and the other was from a CF patient in a geographic area remote f rom Ontario and the United Kingdom. It is evident that the IS402-IS135 6 hybrid element, the cblA pilin subunit gene, and the allelic suite r epresented by multilocus enzyme electrophoretic type ET12 may provide useful markers for the epidemic, highly transmissible transatlantic st rain isolated in Ontario and the United Kingdom.