Molecular characterization of Brucella strains isolated from marine mammals

Abstract

Recently, gram-negative bacteria isolated from a variety of marine mammals have been identified as Brucella species by conventional phenotypic analysis. This study found the 16S rRNA gene from one representative isolate was identical to the homologous sequences of Brucella abortus, B. melitensis, B. canis, and B. suis. IS711-based DNA fingerprinting of 23 isolates from marine mammals showed all the isolates differed from the classical Brucella species. In general, fingerprint patterns grouped by host species. The data suggest that the marine mammal isolates are distinct types of Brucella and not one of the classical species or biovars invading new host species. In keeping with historical precedent, the designation of several new Brucella species may be appropriate.

FIG. 1

DNA sequence of the 16S rRNA gene from Brucella isolate M2357/93 (common seal). A 1,412-bp sequence of the 16S rRNA locus is presented. The sequence is identical to that determined for B. abortus biovar 1 (strain 544) in this study.

FIG. 2

Southern blot analysis of Brucella isolates obtained from marine mammal hosts probed with IS711 DNA. EcoRI genomic digests of 23 Brucella strains were electrophoresed, blotted onto nylon membrane, and probed with DIG-labeled IS711 DNA. Sizes of fragment are given in kilobase pairs on the right side. H. porpoise, harbour porpoise; c. dolphin, common dolphin; c. seal, common seal; h. seal, harbor seal; r. seal, ringed seal; b. dolphin, bottlenose dolphin; and std, size standard (DIG-labeled lambda DNA cut with HindIII). Lanes 1 through 9 contain DNA obtained from hosts in the eastern North Atlantic Ocean or North Sea; lanes 10 through 19 and 21 through 23 contain DNA from hosts found in the eastern Pacific Ocean, Canada, and the western Atlantic Ocean. The arrow indicates a 1.7-kbp fragment common to most isolates. Isolate M336/94 (common seal) is not pictured but has a pattern identical to common seal isolates M972/94 and M339/94.

FIG. 3

Southern blot analysis of two marine mammal isolates and six classical Brucella species probed with IS711 DNA. EcoRI genomic digests of eight Brucella strains were electrophoresed, blotted onto nylon membrane, and probed with DIG-labeled IS711 DNA. Sizes of fragment are given in kilobase pairs on the right side. The arrow indicates the location of the marine-mammal-specific copy of IS711 used for PCR identification.