Diagnostic usefulness of OMP31 from B. melitensis in human and animal brucellosis

CASSATARO J; PASQUEVICH K; BRUNO L; WALLACH JC; FOSSATI CA; BALDI PC

Pamplona, España

Congreso; Brucellosis 2003 International Research Conference; 2003

The group 3 of outer membrane proteins (OMP) of Brucella includes OMP25 and OMP31, which share 34% identity. OMP25 is highly conserved in Brucella species, and OMP31 is present in all species, except B. abortus. Some antigenic differences have been described between OMP31 from B. ovis and that from B. melitensis. We obtained recombinant purified OMP31 (B. melitensis) and tested by indirect ELISA its recognition by sera from humans and animals suffering from brucellosis. Sera from 73 patients, 55 sheep and 31 dogs were analyzed. All patients had yielded hight titers of IgG against Brucella smooth LPS and all but one were also positive for IgG to total cytoplasmic proteins (both measured by ELISA). Blood cultures were available for 52 patients and were positive for Brucella in 29 cases (9 B. suis, 5 B. abortus, 9 B. melitensis and 6 Brucella spp.). Forty-one patients (56%) were positive for antibodies to OMP31, including 5 cases of B. suis infection, 1 of B. abortus, 9 of B. melitensis and 4 of Brucella spp. Among patients included in the study, 34 had yielded negative result for antibodies to a particular cytoplasmic protein of Brucella (lumazine synthase -BLS-); 20 of these patients were positive for antibodies to OMP31. Among 38 sheep infected with B. melitensis (biovars 1 and 3), 24 (63%) were positive for antibodies to OMP31. Anti-OMP31 antibodies were also detected in 12 out of 17 rams (70%) in which B. ovis was isolated from semen. All the 31 dogs included in the study had B. canis isolated from blood and had yielded positive result by direct agglutination (B. canis M-) and by ELISA against cytoplasmic proteins from Brucella. Antibodies to OMP-31 were detected in 25 (80%) of these dogs. These results suggest that an indirect ELISA using recombinant purified OMP31 from B. melitensis would have a limited usefulness for the diagnosis of human and animal brucellosis. Nevertheless, the potential usefulness of this antigen in combination with other recombinant proteins from Brucella should not be dismissed. Notably, 59% of the patients that were negative for anti-BLS antibodies had positive anti-OMP31 reactivity. Regarding B. melitensis infection in sheep, although the percentage of detection remained low, the results obtained by ELISA were largely superior to those obtained previously by other authors using Western blotting.