universe84a

Introduction of Brucella

Major-General Sir David Bruce, in  1886 isolated  Brucella from a spleen of the fatal case, in Malta and the disease called brucellosis. Brucellosis is essentially an infection of animals ( zoonotic disease) mainly of domestic animals, caused by genus Brucella. The other names of brucellosis include (human /animal disease)-

Malta fever/Bang’s disease

Mediterranean fever/epizootic abortion

Undulant fever/enzootic abortion

Rock fever of Gibraltar/slinking of calves

Contagious abortion/spontaneous abortion

Gastric fever/ram epididymitis

Scientific Classification of Brucella

Domain: Bacteria

Phylum: Proteobacteria

Class: Alphaproteobacteria

Order: Rhizobiales

Family: Brucellaceae

Genus: Brucella

Main species of Brucella

• B. melitensis- Sheep, goat
• B. abortus-Cattle
• B. suis-Pig

Morphology of Brucella

Brucellae are coccobacilli or short rod, 0.5 -0.7 × 0.6 -1.5 micron arranged singly or in short chains, aerobic, Gram-negative, non-motile, non-sporing, on capsulated, non-acid fast, and slow-growing. Bipolar staining is common.

Pathogenicity

Sources of infection: Infected animals

Mode of infection: Intestinal tract through consumption of infected milk and milk product

Direct contact: slaughtermen, farmworkers, veterinary surgeons who come in frequent contact with infected animals.

Organisms may enter through the skin, mucosa, and conjunctive.

Lymphatic channels to blood resulting bacteremia – then to the reticuloendothelial system ( liver, spleen, and bone marrow) where organisms multiply inside the cells, leading to developing splenomegaly, hepatomegaly, and also enlargement of lymph nodes. The organism is responsible for Sunderland fever.

Laboratory diagnosis of Brucellosis 

Blood culture

Bone marrow

Lymph node aspirates/biopsy

Spleen aspirates

Occasionally:

Breast Milk,

Vaginal discharge,

Seminal fluid

Culture:

Castaneda’s method of blood culture

( Use of biphasic medium: Trypticase Soy broth and agar/ Serum dextrose broth/ agar)

Note: The addition of bacteria, polymyxin, and cycloheximide makes the medium selective.

Culture characteristic :

Brucella abortus needs an additional 5-10% CO₂for its growth.

Growth is slow and scanty (4-6 weeks incubation is required)

Colonies are small, moist, translucent, and glistening.

Biochemical tests:

Catalase + ve, Oxidase -ve,

The organism is identified based on dye tests, biochemical tests, agglutination with monospecific antisera, and lyses by bacteriophage.

Serological test (Detection of antibodies in patient’s blood):

Culture is often unsuccessful and a lot is allowed to culture Brucella everywhere. Thus culture is not done to diagnose brucellosis.

Following methods are used to estimate antibodies level in the patient’s blood:

• Agglutination test
• Dipstick assay-The dipstick assay is a rapid test in use for the detection of Brucella-specific IgM antibodies.
• Complement Fixation Test (CFT)
• Passive haemagglutination test
• Enzyme-Linked Immunosorbent Assay ( ELISA)
• The lateral flow assay (LFA): The LFA is a simplified version of an ELISA contained in a suitable plastic device.

Antibody levels:

Acute infection:

Antibody titre : more than 1:1000 ( both IgM and IgG)

Disappears after recovery

Chronic infection:

IgM and IgA are raised but not IgM

Healthy contact:

Positive for IgM type of antibodies.

Those who are in touch frequently with infected animals.

Note: 2- Marceptoethanol destroys IgM.

Use of Nucleic Acid Amplification Tests

Amplification strategies-(i) Conventional PCR assays
PCR-enzyme immunoassay (PCR-EIA)
Real-time PCR

Treatment 

Antimicrobial agents commonly used to treat brucellosis include:
doxycycline
streptomycin
ciprofloxacin or ofloxacin.
rifampin
sulfamethoxazole/trimethoprim
tetracycline

Prevention

Following are the preventive measures for brucellosis-

• Evitate the consumption of raw meat or unpasteurized milk, cheese, and ice cream.
• Wear gloves and protective glasses when handling animal or animal tissues.
• Cover any open wounds on your skin when you come into contact with animal blood.
• Wear protective clothing and gloves to help give birth to animals.

Key Notes on Brucella

• David Bruce was an Australian-born British pathologist and microbiologist who investigated Malta fever and African trypanosomiasis. He discovered a protozoan parasite transmitted by insects, later named Trypanosoma brucei after him.
• Brucella organisms multiply and concentrate within the reticuloendothelial system and therefore the growth of these macrophage-rich tissues may increase the recovery of bacteria.
• Bone marrow cultures are the diagnostic gold standard as compared to blood.
• Brucella comes under the risk group 3 organism and thus may cause laboratory-acquired infection due to conventional methods of culturing and thus manual biphasic methods i.e. Castañeda flask was designed by Ruiz-Castañeda in the late 1940s to obviate the necessity of performing repeat blind subcultures to minimize infection.
• Brucella organisms are also agents of biowarfare.
• The Bactec system is superior for recovering brucellae.
• The matrix-assisted laser desorption ionization-time of flight mass spectrometry (MALDI-TOF) technology is really very useful in the clinical microbiology laboratory for the identification of microorganisms in the following ways- make possible the fast, accurate, reproducible, and cost-effective identification of isolates to the species level, replacing tedious biochemical testing. But even to its technical simplicity, the MALDI-TOF instrument is particularly suitable for use in busy laboratories, where it can be operated by less-skilled technicians.
• Infective dose: between 10 and 100 organisms

Further Reading 

1. https://cmr.asm.org/content/33/1/e00073-19
2. https://www.sciencedirect.com/topics/immunology-and-microbiology/brucella
3. https://emedicine.medscape.com/article/213430-overview
4. https://www.who.int/csr/resources/publications/Brucellosis.pdf
5. https://www.who.int/news-room/fact-sheets/detail/brucellosis