Diagnosis of human and animal brucellosis using extracts of bacteria phylogenetically related to Brucella

M. VICTORIA DELPINO; JORGE WALLACH; CARLOS A. FOSSATI; PABLO C. BALDI

España

Congreso; Brucellosis 2003 International Research Conference.; 2003

Abstract Members of the genus Brucella are gram negative bacteria that cause brucellosis, an infectious disease affecting livestock and humans, and whose laboratory diagnosis is usually performed by bacteriological and serological tests. Brucella sp, Agrobacterium sp, Sinorhizobium sp and Ochrobactrum sp are gram negative bacteria of the a-2 subgroup of the domain Proteobacteria. We studied the potential usefulness of cytoplasmic proteins of some representative bacteria of this subgroup as antigens in an indirect ELISA to diagnose brucellosis in humans (n=32), sheep (n=75), cows (n=59), and dogs (n=61) Sera from infected humans, sheep and cows were all positive for antibodies against lipopolysaccharides and cytoplasmatic protein of Brucella sp by ELISA. Proteins from A. tumefaciens, S. meliloti and O. anthropi were obtained by French press disruption, followed by ultracentrifugation and DNAse and RNAse digestion. Cut-off values were calculated as mean ± SD of specific optical densities (sOD= OD with antigen – OD without antigen) obtained with normal sera (humans, 20; sheep, 20; cows, 36; dogs, 34). Canine infection by B. canis was detected with high specificity (97,6% for Agrobacterium, 93,3% for Sinorhizobium, 100% for Ochrobactrum) and sensitivity(32% for Agrobacterium, 77% for Sinorhizobium, 100% for Ochorbactrum) by all the ELISAs tested, and it was possible to diagnose the disease shortly after the exposure to the pathogen (15 days). In contrast, normal sera from humans, sheep, and cattle yielded high sOD with all the antigens, which resulted in high cut-off values and, consequently, in low sensitivities. For human sera, cut-off values were 2.550 for Agrobacterium, 1.820 for Sinorhizobium, 1.500 for Ochrobactrum; for sheep, cut off values were 1.821, 1.255, 0.856 for, respectively; for cattle cut off values were 0.822, 0930, 0.665, respectively. These results show that antibodies to cytoplasmatic proteins antibodies of related proteobacteria have no diagnostic role in ovine, bovine and human brucellosis, But it was highly specific and sensitive for the diagnosis of canine brucellosis and can detect the infection by B. canis shortly after the exposure to the pathogen.