Brucella

Bacteriology Brucella
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Brucella Brucella
? Clinical Manifestations
Brucellosis is a severe acute febrile disease? caused by bacteria of the genus Brucella. Relapses are not uncommon; focal lesions may occur in bones, joints, genitourinary tract, and other sites. Hypersensitivity reactions can follow occupational exposure. Infection may be subclinical. Chronic infections may occur.
? Structure
Brucellae are Gram-negative coccobacilli; non-spore-forming and non-motile; aerobic, but may need added CO2.
? Classification and Antigenic Types
Three species? (B melitensis, B abortus, B suis) are important human pathogens; B canis is of lesser importance. Species are differentiated by
1. production of urease
2. H2S, dye sensitivity, cell wall antigens
3. phage sensitivity. The major species are divided into multiple biovars.
? Pathogenesis
Portals of entry are the mouth, conjunctivae, respiratory tract and abraded skin. Organisms spread, possibly in mononuclear phagocytes, to reticuloendothelial sites. Small granulomas reveal a mononuclear response; hypersensitivity is a major factor.
? Host Defenses
Effective host defense depends mainly upon cell-mediated immunity.
? Epidemiology
Brucellosis is a zoonosis, acquired from handling of infected animals or consuming contaminated milk or milk products. Exposure is frequently occupational. The disease is now uncommon in the United States and Britain but common in the Mediterranean and Arabian Gulf regions, Latin America, Africa, and parts of Asia.
Bacteriology Brucella
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? Diagnosis
Diagnosis can be made clinically if there is a history of exposure. Blood cultures may be positive in early disease but serology is mainstay of diagnosis. Interpretation is complicated by subclinical infections and persistent levels of antibody.
? Control
Brucellosis is prevented by pasteurizing milk, eradicating infection from herds and flocks, and observing safety precautions (protective clothing and laboratory containment). The disease is treated with doxycycline, streptomycin and rifampin.
? Introduction
Bacteria of the genus Brucella cause disease primarily in domestic, feral and some wild animals and most are also pathogenic for humans. In animals, brucellae typically affect the reproductive organs?, and abortion? is often the only sign of the disorder. Human brucellosis is either :
1. acute febrile disease, or:
2. persistent disease with a wide variety of symptoms.
It is a true zoonosis in that virtually all human infections are acquired from animals. The disease is controlled by the routine practice of pasteurizing milk and milk products, as well as by comprehensive campaigns to eradicate the disease by destroying domestic animals which exhibit positive serologic reactions to brucellae. Vaccines providing some protection to cattle, sheep and goats are available.
? Clinical Manifestations
The presentation of brucellosis is characteristically variable. The incubation period is often difficult to determine but is usually from 2 to 4 weeks. The onset may be insidious or abrupt. Subclinical infection is common.
?In the simplest case,
? the onset is influenza-like with fever reaching 38 to 40°C.
? Limb and back pains are unusually severe, however, and
? sweating and fatigue are marked.
? The leukocyte count tends to be normal or reduced, with a relative lymphocytosis.
? On physical examination, splenomegaly may be the only finding.
Bacteriology Brucella
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If the disease is not treated, the symptoms may continue for 2 to 4 weeks. Many patients will then recover spontaneously but others may suffer a series of exacerbations. These may produce an ?undulant fever in which the intensity of fever and symptoms recur and recede at about 10 day intervals. Anemia is often a feature. True relapses may occur months after the initial episode, even after apparently successful treatment.
?Most affected persons recover entirely within 3 to 12 months but some will develop complications marked by involvement of various organs, and a few may enter an ill-defined chronic syndrome.
Complications include;
? Arthritis
? often sacroiliitis
? spondylitis (in about 10 percent of cases)
? central nervous system effects including meningitis (in about 5%)
? uveitis
? epididymoorchitis.
In contrast to animals, abortion is not a feature of brucellosis in pregnant women. Hypersensitivity reactions, which may mimic the symptoms of an infection, may occur in individuals who are exposed to infective material after previous, even subclinical, infection.
? Structure
Brucellae are Gram-negative coccobacilli (short rods) measuring about 0.6 to 1.5 ?m by 0.5-0.7 ?m. They are non-sporing and ?lack capsules or flagella and, therefore, are non-motile. The outer cell membrane closely resembles that of other Gram-negative bacilli with a dominant lipopolysaccharide (LPS) component and three main groups of proteins. The G+C content of the DNA is 55-58 moles/cm. ?No Brucella species has been found to harbor plasmids naturally although they readily accept broad-host-range plasmids.
The metabolism of the brucellae is mainly oxidative and they show little action on carbohydrates in conventional media. They are aerobes but some species require an atmosphere with added CO2(5-10 percent). ??Multiplication is slow at the optimum temperature of 37°C and enriched medium is needed to support adequate growth.
????Brucella colonies become visible on suitable solid media in 2-3 days. The colonies of smooth strains are small, round and convex but dissociation, ??with loss of the O chains of the LPS, occurs readily to form rough or mucoid variants. These latter forms are natural in B canis and B ovis as the LPS of these ??lack O chains.
Bacteriology Brucella