Characterization of integrons in Burkholderia cepacia clinical isolates

Burkholderia cepacia is an opportunistic pathogen able to colonize the airways of Cystic Fibrosis (CF) patients, frequently developing chronic infections. In 20% of cases these infections cause severe and poorly controlled pathological situations because of the intrinsic antibiotic resistance expressed by the microorganism. CF patients are often subjected to antibiotic therapy: this facilitates the acquisition of antibiotic resistance determinants by the infecting bacteria. Integrons are mobile genetic elements that are widespread in bacterial populations and favor the acquisition of gene cassettes coding for these determinants.The presence of class 1 integrons was investigated by PCR with primers specific for the 5’ and 3’ ends in Burkholderia isolates recovered from patients in treatment at the CF center of Friuli Venezia Giulia. The same integron, carrying an uncommon allelic form (Ib) of the aacA4 gene in its cassette array and conferring resistance to some aminoglycosides, was found in two independent isolates (different RAPD profiles) infecting two different patients. In both isolates the integron was carried by plasmids and was still present 3 and 6 years later the first finding. Despite the exchange of integrons between bacterial pathogens is fully described, these items were not frequently found in Burkholderia isolates. Although the clinical relevance of the integron we identified is low (a single gene cassette encoding a widespread resistance),we feel concerned that these genetic elements begin to circulate in this bacterial species, as this could make more and more troublesome the treatment of infections notoriously difficult to eradicate.