Summary auto-generated
This study investigated the genetic and antigenic relationship between Brucella species and Ochrobactrum anthropi using protein profiling, Western blotting, immunoelectrophoresis, and 16S rRNA sequence analysis. The researchers analyzed multiple bacterial strains and found that O. anthropi is heterogeneous, consisting of at least two distinct groups previously identified by DNA-DNA hybridization. Analysis of 16S rRNA sequences revealed that strains LMG 3301 and LMG 3306 are more closely related to Brucella species than to the O. anthropi type strain (LMG 3331T). Western blot analysis of whole-cell protein extracts confirmed this closer relationship, showing that LMG 3301 clustered with Brucella rather than with LMG 3331T. The two groups could also be differentiated by colistin sensitivity and PCR using Brucella-specific 16S rRNA primers. The authors additionally identified this distinction in clinical isolates previously classified as O. anthropi. Based on these findings, the researchers propose establishing a new species, Ochrobactrum intermedium, for the LMG 3301 cluster and related strains that show greater phylogenetic and antigenic similarity to Brucella than to typical O. anthropi.
Key findings
- O. anthropi is heterogeneous; strains LMG 3301 and LMG 3306 are more closely related to Brucella species than to the O. anthropi type strain LMG 3331T based on 16S rRNA sequence analysis
- Western blot analysis of whole-cell proteins showed the LMG 3301 cluster grouped with Brucella species while LMG 3331T grouped with Agrobacterium, despite conventional phenotypic tests classifying both as O. anthropi
- The two O. anthropi groups can be differentiated by colistin sensitivity and PCR with Brucella 16S rRNA primers, with some clinical isolates belonging to the LMG 3301 cluster
- The authors propose the name Ochrobactrum intermedium sp. nov. for the LMG 3301 cluster due to its intermediate position and closer relationship to Brucella than to O. anthropi sensu stricto
- Serological cross-reactivity was more intense between Brucella and O. anthropi strains than with Agrobacterium species, supporting their closer evolutionary relationship
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Abstract
The relatedness of Brucella spp. and Ochrobactrum anthropi was studied by protein profiling, Western blot, immunoelectrophoresis and 16S rRNA analysis. Whole-cell and soluble proteins of brucellae and O. anthropi showed serological cross-reactivities quantitatively and qualitatively more intense than those existing with similar extracts of Agrobacterium spp. Numerical analysis of Western blot profiles of whole-cell extracts showed that O. anthropi LMG 3301 was closer to Brucella spp. than to O. anthropi LMG 3331Ta result not obtained by protein profiling. These differences were not observed by Western blot with soluble fractions, and immunoelectrophoretic analyses suggested that this was due to destruction of conformational epitopes in Western blot procedures with the subsequent simplification of antigenic profile. Analysis of the 16S rRNA sequences of strains previously used in the species definition confirmed that strain LMG 3301, and also LMG 3306, were closer to the brucellae, and that LMG 3331Twas in a separate cluster. The LMG 3301 and the LMG 3331Tclusters could also be separated by their different colistin sensitivity and by PCR with 16S rRNA Brucella primers, and both methods showed strains of both clusters among clinical isolates classified as O. anthropi by conventional tests. These results and those of previous DNA-DNA hybridization studies [Holmes, B., Popoff, M., Kiredjian, M. & Kersters, K. (1988). Int J Syst Bacteriol 38, 406–416] show that the LMG 3301 cluster and related clinical isolates should be given a new species status for which the name Ochrobactrum intermedium sp. nov. is proposed (type strain is LMG 3301T= NCTC 12171T= CNS 2-75T).