This document provides information on Brucella, the causative agent of brucellosis. It discusses that Brucella is a gram-negative coccobacillus that can infect various domestic animals and cause zoonotic infections in humans. The four main human pathogenic species are B. abortus, B. melitensis, B. suis, and B. canis. Brucellosis is transmitted to humans primarily through the consumption of contaminated, unpasteurized dairy products. The disease causes acute or chronic systemic infections and can occasionally lead to localized complications like endocarditis. Laboratory diagnosis involves culture and serological tests. Treatment involves prolonged courses of antibiotic combinations like doxycycline and rifamp

1. Chapter 5:
Special Bacteriology
BEMS
Syeda Ambreena Batool

2. Gram Negative Bacilli

3. Brucella
• Brucellosis is primarily a zoonotic infection
caused by Brucella organisms infecting the
domestic animals.
• The condition is known by various names, such
as Malta fever, Mediterranean fever, undulant
fever

4. Brucella
• Family : Brucellaceae
• Genus : Brucella
• The genus Brucella consists of seven species,
four of which are human pathogens. These are
Brucella abortus(cattle), Brucella
melitensis(goats, sheep), Brucella suis(swine),
and Brucella canis(dogs).

5. Morphology
• Brucellae are Gram negative, but
counterstain poorly and require
relatively more time for staining.
• They are small coccobacilli,
measuring 0.5–0.7 x 0.6–1.5μm in
size.
• These are arranged singly or in
short chains.
• The genus Brucella is small,
nonmotile, nonsporing,
nontoxigenic, nonfermenting
aerobic, and Gram-negative
coccobacilli .

6. Pathogenesis and Immunity
Brucella species have predilection for intracellular growth
hence may be demonstrated inside phagocytes.
Virulence Factor: Brucella produces the following
virulence factors:
a)LPS
b)Intracellular location of the bacterium.

8. • Pathogenesis :Brucella enter through:
• Abrasion or cut in the skin
• Conjunctiva
• Respiratory tract
• Gastrointestinal tract
• Shortly after gaining entry to the body, brucellae are rapidly
ingested by polymorphonuclear leukocytes, which are
attracted to the site of inflammation. But inside the
leukocytes, the brucellae are not killed due to the presence of
enzyme superoxide dismutase, O polysaccharide of LPS, and
nucleotide-like substances produced by the bacteria.

9. • Brucellae that are not killed by leukocytes spread from the
site of infection to the local lymph nodes which drain the site
of infection. Inside the lymph glands, the bacteria multiply
and are released to the blood stream following rupture of the
cells and are phagocytosed by the macrophages.
• Bacteria present in the macrophages are then carried to the
organs of reticuloendothelial system, such as liver, spleen,
bone marrow, lymph nodes, and kidney. In these organs,
brucellae multiply in phagosomes of macrophages due to
production of adenine and guanine monophosphate, which
inhibits the phagolysosome fusion, oxidative burst activity,
and tumor necrosis factor production.

11. • Host Immunity : Immunity in brucellosis, like other
obligate intracellular pathogens, is primarily cell-mediated
immunity.
• The humoral immunity is characterized by production of
antibodies against LPS of the bacteria.
• Clinical Syndromes:
• B.melintensis is the most virulent species. It causes the most
severe and acute cases of brucellosis. It is also the most
common cause of brucellosis (survive in phagocytic cells
and multiply in them, it produces a large number of
bacteria.)
• B.suis is associated with a prolonged course of illness often
with suppurative, destructive lesions.
• B.abortus causes mild to moderate sporadic disease that is
rarely associated with complications.
• B.canis infection is associated with an insidious onset, more
relapses.

12. ◗ Brucellosis
• The incubation period may range from 3 days to several
weeks. Human infections may be of three types, as
follows:
• (a) acute brucellosis.
• (b) chronic brucellosis.
• (c) localized infection.
• Acute brucellosis
• Undulant fever.
• Headache.
• Limb and back pains are unusually severe, night sweating
and fatigue are marked.
• Anorexia, weakness, loss of weight, depression.

13. • Chronic brucellosis This condition develops in incompletely
treated patients.
• It is usually non bacteremic.
• There is lassitude sweating and joint pain.
• Symptoms often last for 3–6 months and occasionally for a year or
more.
• Localized infection
• B. suis is more likely to cause localized and suppurative infection.
Complications include infections of the heart, central nervous
system (CNS), and the skin.
• Brucella endocarditis is the most dangerous complication and is
responsible for 80% of deaths in brucellosis.
• Chronic meningoencephalitis is the usual manifestation of CNS
infection.

14. Transmission source
• Unpasteurized milk
• The infected animals, such as cattle, goats, sheep,
buffalos, and swine are the important reservoirs of
infections.
• Brucella organism is transmitted to humans by the
following ways:
(b) Ingestion
(a) inhalation.
(c) direct contact.
(d) accidental inoculation.

15. (a) Ingestion: Brucellosis results primarily by drinking
contaminated unpasteurized milk or milk products. The infection
can also be transmitted by drinking water or eating raw vegetables
contaminated with feces or urine of infected animals and also by
eating meat of infected animals.
(b) Inhalation: The infection is transmitted by inhalation of dust
from wool or other dried material of infected animals. Infection by
inhalation is important among veterinarians and laboratory workers.
(c) Direct contact: The infection is acquired by direct contact
with the infected materials of septic abortion of the animals or at
the time of slaughter of animals. Brucella species present in the
infected materials (placenta, fetuses, vaginal discharge, urine, or
infected carcasses) enter the human host through the mucosa,
conjunctiva, or skin.
(d) Accidental inoculation: Accidental inoculation is a serious
risk in laboratory workers who handle culture of the organism.

16. Laboratory Diagnosis
• Specimens Blood,bone marrow, and sometime synovial
fluid and pleural fluid is the specimen of choice and is
collected for culture and for serological test.
• Microscopy Gram staining is not useful for
demonstration of Brucella organisms in clinical
specimens due to their small size and intracellular
location.
• Culture brucella is isolated from a blood culture on
Castaneda medium or from bone marrow. Prolonged
incubation (up to six weeks) may be required, as they are
slow-growing, but on modern automated machines, the
cultures often show positive results within 7 days.

17. Idenfication of Brucella
• Brucellae are strict aerobes.
• Produce small, moist, translucent, and glistening colonies
after 3 or more days.
• Growth in the presence of aniline dyes, such as basic fuchsin
dyes or thionine.
• Oxidase positive.
• Agglutination with specific antibrucella sera.
• Susceptibility to lysis by bacteriophage.
• They grow at a temperature range of 22–40°C and pH range
of 6.6–7.4 .
• Grow best in medium enriched with glucose and animal
serum.

18. Serological Tests
• Serological tests are useful for diagnosis of subclinical
brucellosis and for cases of acute and chronic brucellosis by
demonstration of specific antibodies in patient’s serum.
• Specific brucella antibodies, both IgG and IgM antibodies,
appear in the serum 7–10 days after infection. IgM antibodies
persist for up to 3 months after which these antibodies
decline. Then IgG and IgA antibodies appear after 3 weeks of
infection and persist for longer time.
• A number of serological tests have been developed and
tested in serodiagnosis of brucellosis. Common methods are:
• (a) standard tube agglutination tests.
• (b) indirect immunofluorescent tests.
• (c) enzyme-linked immunosorbent assay (ELISA).

19. Treatment
• Tetracycline
• Streptomycin + tetracycline
• Rifampicin + doxycycline
• The combination of antibiotics is recommended whenever
possible.

20. Prevention and Control
• Pasteurization or boiling of milk
• Use of protective clothing and gloves by persons
handling or coming into close contact with animals.
• Vaccine: Vaccination of animals is effective to control
brucellosis in animals. Live attenuated B. abortus vaccine
containing B. abortus 1019 strain has been used
successfully to prevent infection in cattle. Vaccines are
not available against either B. suis or B. canis. No vaccine
is available for humans.

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