Brucellosis is a zoonotic disease transmitted from infected animals to humans through contact with bodily fluids or unpasteurized dairy. It causes significant illness in both animals and humans. Blood culture is the gold standard for diagnosis but has variable success rates. Serologic testing is more common and detects antibodies but has limitations including potential cross-reactivity with other bacteria. False positives can also occur due to cross-reactivity with antigens on other gram-negative bacteria. The lipopolysaccharide is a major virulence factor in Brucella that varies between strains impacting pathogenicity and ability to induce protective immunity.

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INTRODUCTION
• Brucellosis is a zoonotic infection transmitted to humans by contact
with fluids from infected animals (sheep, cattle, goats, pigs, or other
animals) or derived food products such as unpasteurized milk and
cheese. It is one of the most widespread zoonoses worldwide.
Brucellosis has high morbidity both for humans and animals; it is an
important cause of economic loss and a public health problem in many
developing countries .

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• DIAGNOSIS
• Blood culture is considered the diagnostic gold standard, but isolation rates may
vary considerably (25%–80%) depending on stage of infection, previous use of
antibiotics, type and volume of clinical specimen, and culture method used.
Bacterial growth can be observed within 3–5 days in culture but may take longer;
therefore, cultures should be held for ≥10 days before considering the sample
culture-negative.

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• To increase recovery of the organism when focal disease is suspected,
samples for culture should be collected from the affected area (for
example, cerebrospinal fluid, joint aspirate, or urine). Inform the
laboratory if brucellosis is suspected when submitting blood, bone
marrow, or other clinical specimen for culture, as the bacteria take
longer to grow, and laboratory personnel require additional personal
protective equipment when handling.

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• Serologic testing
• Serologic testing is the most common method for diagnosis. The
serum agglutination test (SAT) is the standard method for serologic
diagnosis and detects IgM, IgG, and IgA. In general, ELISA tests have
good sensitivity and specificity and can detect IgM and IgG.

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• Some limitations to the use of serologic tests must be taken into
consideration when diagnosing Brucella infections, as most serologic
assays for brucellosis show variable levels of cross-reactivity with
other gram-negative bacteria (for example, E. coli O:157, FrancisElla
tularensis, and Yersinia enterocolitica). Brucella antibodies can persist
for more than a year despite successful antibiotic treatment.

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• Last, no validated serologic assays are available to detect antibodies
produced against infections caused by B. canis and B. abortus RB51
strain. If infection by either of these organisms is possible or
suspected, culture should be performed.

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• Causes of false positive or negative brucellosis.
• Cross-reactions and false-positivte test results can occur in Brucella
antibody tests. The primary immune determinant and virulence factor
for Brucella species is the cell wall surface lipopolysaccharide, which
is antigenically similar to the lipopolysaccharide of other gram-
negative rods.

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• False-positive Brucella antibody test results can be caused by cross-
reactivity of antibodies to Escherichia coli O157, Francisella
tularensis, Moraxella phenyl pyruvica, Yersinia enterocolitica, and
certain Salmonella species (9). Most cross-reacting antibodies are IgM
(10), making interpretation of any IgM assay difficult because of false
positivity. Therefore, results obtained using EIA should be confirmed
by a reference method.

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• variation
• The lipopolysaccharide (LPS) is considered the major virulent factor
in Brucella spp. Several genes have been identified involved in the
synthesis of the three LPS components: lipid A, core and O-PS.
Usually, Brucella strains devoid of O-PS (rough mutants) are less
virulent than the wild type and do not induce undesirable interfering
antibodies. Such of them proved to be protective against brucellosis in
mice. Because of these favorable features, rough strains have been
considered potential brucellosis vaccines.

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• In this study, we evaluated the antigenic, immunologic and genetic
characteristics of rough strains B.abortus RB51, B.melitensis B115
and B.melitensis B18. RB51 derived from B.abortus 2308 virulent
strain and B115 is a natural rough strain in which the O-PS is present
in the cytoplasm. B18 is a rough rifampin-resistan mutant isolated in
our laboratory.

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• The surface antigenicity of RB51, B115 and B18 was evaluated by
testing their ability to bind antibodies induced by rough or smooth
Brucella strains. The antibody response induced by each strain was
evaluated in rabbits. Twenty-one genes, involved in the LPS-synthesis,
were sequenced and compared with the B.melitensis 16M strain.n

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• The results indicated that RB51, B115 and B18 have differences in
antigenicity, immunologic and genetic properties. Particularly, in B115
a nonsense mutation was detected in wzm gene, which could explain
the intracellular localization of O-PS in this strain.
• Complementation studies to evaluate the precise role of each mutation
in affecting Brucella morphology and its virulence, could provide
useful information for the assessment of new, attenuated vaccines for
brucellosis.