An IS711 element downstream of the bp26 gene is a specific marker of Brucella spp. isolated from marine mammals

DNA polymorphism of the bp26 gene, coding for a diagnostic protein antigen for brucellosis, was assessed by PCR and restriction fragment length polymo rphism analysis using primers to amplify the bp26 gene with its flanking re gions. Surprisingly, whereas PCR performed on DNA of the reference strains of the six recognized Brucella species produced a product of the expected s ize (1,029 bp), PCR performed on DNA of three representative strains from m arine mammals (from a seal, a dolphin, and a porpoise) produced a larger pr oduct, of about 1,900 bp. Nucleotide sequencing of the 1,900-bp PCR product s revealed the presence of an insertion sequence, IS711, downstream of the bp26 gene and adjacent to a Bru-RS1 element previously described as being a hot spot for IS711 insertion. PCR performed on a large number of field str ains from different geographic origins and from marine mammal isolates indi cated that the occurrence of an IS711 element downstream of the bp26 gene N as a feature specific to the marine mammal Brucella strains. Thus, this PCR assay is able to differentiate Brucella terrestrial isolates from marine m ammal isolates and could be applied far diagnostic purposes.