Brucellosis 2003 proceedings - PHIDIAS

Poster Session
controversial. While the concentration of 2-mercaptoethanol used in the test is
assumed to destroy only IgM, the extent to which IgG is affected has never been
addressed. We conducted a comparison between 2ME titers and levels of IgG to
Brucella smooth lipopolysaccharide (LPS) measured by ELISA in 158 serum samples
referred to our laboratory. These samples were from people with confirmed recent or
past brucellosis (patients), individuals with positive slide agglutination in blood bank
or pre-laboral tests, and persons with symptoms compatible with brucellosis that
were referred for serological confirmation of the disease (suspected brucellosis). Anti-
LPS IgG levels were expressed as a positivity index (PI), calculated as the optical
density yielded by each sample divided by the cut-off of the assay. Anti-LPS IgG was
considered negative when the PI was < 1, weakly positive for PI between 1 and 2,
and strongly positive when the PI was higher than 2. Sixty-four samples were
negative by 2ME, 20 were positive with a titer of 25, 28 yielded a titer of 50, and 46
had a titer of 100 or higher. Anti-LPS IgG was strongly positive for 52 (81%), 19
(95%), 26 (93%), and 46 (100%) of these samples, respectively. A separate analysis
was performed for the samples that showed the most discordant results (negative or
25 by 2ME, strongly positive by ELISA). The standard tube agglutination (STA) had
yielded significant titers (ò100) in 13 (25%) of the 52 samples with negative 2ME and
in 8 (42%) of the 19 samples with a 2ME titer of 25. Among the 52 subjects with
negative 2ME and high levels of IgG, 32 had documented recent or past brucellosis,
including 25 (48%) with current clinical manifestation; other 18 individuals had
compatible symptoms but lacked bacteriological confirmation of the disease. Among
subjects with a 2ME titer of 25, 14 (74%) had documented brucellosis with current
clinical manifestation. These results suggest that a significant proportion of patients
with active brucellosis are missed by the 2ME test, but can be correctly diagnosed if
anti-LPS IgG is measured by ELISA.
39- DIAGNOSTIC USEFULNESS OF Omp31 FROM B. melitensis IN HUMAN AND
ANIMAL BRUCELLOSIS.
J. Cassataro 1 , K. Pasquevich, L. Bruno 1 , J.C. Wallach 2,3 , C. A Fossati 2 , and P.C. Baldi 2 . (1)
Laboratorio de Inmunogenética, Hospital de Clínicas, Universidad de Buenos Aires, Argentina. (2)
Servicio de Brucelosis, Hospital F.J. Muñiz, Buenos Aires, Argentina. (3) IDEHU, Facultad de
Farmacia y Bioquímica, Universidad de Buenos Aires, Buenos Aires, Argentina.
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
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Brucellosis 2003 International Research Conference