| Summary: | <p>Abstract</p> <p>Background</p> <p>Brucellosis is a zoonosis caused by <it>Brucella </it>spp., a group of highly homogeneous bacteria. The insertion sequence IS<it>711 </it>is characteristic of these bacteria, and occurs in variable numbers and positions, but always constant within a given species. This species-associated polymorphism is used in molecular typing and identification. Field isolates of <it>B. abortus</it>, the most common species infecting cattle, typically carry seven IS<it>711 </it>copies (one truncated). Thus far, IS<it>711 </it>transposition has only been shown <it>in vitro </it>and only for <it>B. ovis </it>and <it>B. pinnipedialis</it>, two species carrying a high number of IS<it>711 </it>copies, but never in other <it>Brucella </it>species, neither <it>in vitro </it>nor in field strains.</p> <p>Results</p> <p>We found several <it>B. abortus </it>strains isolated from milk and aborted fetuses that carried additional IS<it>711 </it>copies in two hitherto undescribed insertion sites: one in an intergenic region near to the 3' end of a putative lactate permease gene and the other interrupting the sequence of a <it>marR </it>transcriptional regulator gene. Interestingly, the second type of insertion was identified in isolates obtained repeatedly from the same herd after successive brucellosis outbreaks, an observation that proves the stability and virulence of the new genotype under natural conditions. Sequence analyses revealed that the new copies probably resulted from the transposition of a single IS<it>711 </it>copy common to all <it>Brucella </it>species sequenced so far.</p> <p>Conclusions</p> <p>Our results show that the replicative transposition of IS<it>711 </it>can occur under field conditions. Therefore, it represents an active mechanism for the emergence of genetic diversity in <it>B. abortus </it>thus contributing to intra-species genetic polymorphism.</p>
|
|---|
