Brucella
Encyclopedia
Brucella is a genus
Genus
In biology, a genus is a low-level taxonomic rank used in the biological classification of living and fossil organisms, which is an example of definition by genus and differentia...

 of Gram-negative
Gram-negative
Gram-negative bacteria are bacteria that do not retain crystal violet dye in the Gram staining protocol. In a Gram stain test, a counterstain is added after the crystal violet, coloring all Gram-negative bacteria with a red or pink color...

 bacteria. They are small (0.5 to 0.7 by 0.6 to 1.5 µm), non-motile, non-encapsulated coccobacilli
Coccobacillus
A coccobacillus is a type of rod-shaped bacteria. The word coccobacillus reflects an intermediate shape between coccus and bacillus . Coccobacilli rods are so short and wide that they resemble cocci. Haemophilus influenzae and Chlamydia trachomatis are coccobacilli...

, which function as facultative intracellular parasites.

Brucella is the cause of brucellosis
Brucellosis
Brucellosis, also called Bang's disease, Crimean fever, Gibraltar fever, Malta fever, Maltese fever, Mediterranean fever, rock fever, or undulant fever, is a highly contagious zoonosis caused by ingestion of unsterilized milk or meat from infected animals or close contact with their secretions...

, which is a zoonosis
Zoonosis
A zoonosis or zoonoseis any infectious disease that can be transmitted from non-human animals to humans or from humans to non-human animals . In a study of 1415 pathogens known to affect humans, 61% were zoonotic...

. It is transmitted by ingesting infected food, direct contact with an infected animal, or inhalation of aerosols. Transmission from human to human, for example through sexual intercourse or from mother to child, is exceedingly rare, but possible. Minimum infectious exposure is between 10 - 100 organisms. Brucellosis primarily occurs through occupational exposure (e.g. exposure to cattle, sheep, pigs), but also by consumption of unpasteurized
Pasteurization
Pasteurization is a process of heating a food, usually liquid, to a specific temperature for a definite length of time, and then cooling it immediately. This process slows microbial growth in food...

 milk products.

There are a few different species of Brucella, each with slightly different host specificity. B. melitensis
Brucella melitensis
-Introduction:Brucella melitensis is a gram negative coccobacillus bacteria from the Brucellaceae family. The bacterium causes Ovine Brucellosis, along with Brucella ovis. It can infect sheep, cattle, and sometimes humans and it can be transmitted by the stable fly...

which infects goat
Goat
The domestic goat is a subspecies of goat domesticated from the wild goat of southwest Asia and Eastern Europe. The goat is a member of the Bovidae family and is closely related to the sheep as both are in the goat-antelope subfamily Caprinae. There are over three hundred distinct breeds of...

s and sheep, B. abortus which infects cattle
Cattle
Cattle are the most common type of large domesticated ungulates. They are a prominent modern member of the subfamily Bovinae, are the most widespread species of the genus Bos, and are most commonly classified collectively as Bos primigenius...

, B. suis infects pigs, B. ovis
Brucella ovis
Brucella ovis is a gram negative coccobacillus from the Brucellaceae family. Along with Brucella melitensis, it is responsible for causing Ovine Brucellosis, which is a notifiable disease...

infects sheep and B. neotomae. Recently new species were discovered, in marine mammals (B. pinnipedialis and B. ceti ), in the common vole Microtus arvalis (B. microti ), and even in a breast implant (B. inopinata ). One unnamed strain (Brucella sp. NVSL 07-0026) has been isolated from a baboon.

However, the new NCBI
NCBI
NCBI may refer to:* National Center for Biotechnology Information, part of the U.S. National Institutes of Health* National Coalition Building Institute, a U.S. non-profit training group...

 taxonomy has named all Brucella species Brucella melitensis. They include Brucella melitensis 16M and 5 other biovars: abortus, canis, neotomae, ovis, and suis.

Diagnosis

Brucella is isolated from a blood culture
Blood culture
Blood culture is a microbiological culture of blood. It is employed to detect infections that are spreading through the bloodstream...

 on Castaneda medium. Prolonged incubation (up to 6 weeks) may be required as they are slow-growing, but on modern automated machines the cultures often show positive results within seven days. On Gram stain they appear as dense clumps of Gram-negative
Gram-negative
Gram-negative bacteria are bacteria that do not retain crystal violet dye in the Gram staining protocol. In a Gram stain test, a counterstain is added after the crystal violet, coloring all Gram-negative bacteria with a red or pink color...

 coccobacilli and are exceedingly difficult to see. In recent years molecular diagnostic techniques based on the genetic component of the pathogen have become more popular.

It is crucial to be able to differentiate Brucella from Salmonella
Salmonella
Salmonella is a genus of rod-shaped, Gram-negative, non-spore-forming, predominantly motile enterobacteria with diameters around 0.7 to 1.5 µm, lengths from 2 to 5 µm, and flagella which grade in all directions . They are chemoorganotrophs, obtaining their energy from oxidation and reduction...

which could also be isolated from blood culture
Blood culture
Blood culture is a microbiological culture of blood. It is employed to detect infections that are spreading through the bloodstream...

s and are Gram-negative. Testing for urease
Urease
Urease is an enzyme that catalyzes the hydrolysis of urea into carbon dioxide and ammonia. The reaction occurs as follows:In 1926, James Sumner showed that urease is a protein. Urease is found in bacteria, yeast, and several higher plants. The structure of urease was first solved by P.A...

 would successfully accomplish the task; as it is positive for the Brucella and negative for the Salmonella.

Brucella could also be seen in bone marrow
Bone marrow
Bone marrow is the flexible tissue found in the interior of bones. In humans, bone marrow in large bones produces new blood cells. On average, bone marrow constitutes 4% of the total body mass of humans; in adults weighing 65 kg , bone marrow accounts for approximately 2.6 kg...

.

Laboratory acquired brucellosis is common. This most often happens when the disease is not thought of until cultures become positive, by which time the specimens have already been handled by a number of laboratory staff. The idea of preventive treatment is to stop people who have been exposed to Brucella from becoming ill with the disease.

There are no clinical trials to be relied on as a guide for optimal treatment, but a three week course of rifampicin
Rifampicin
Rifampicin or rifampin is a bactericidal antibiotic drug of the rifamycin group. It is a semisynthetic compound derived from Amycolatopsis rifamycinica ...

 and doxycycline
Doxycycline
Doxycycline INN is a member of the tetracycline antibiotics group, and is commonly used to treat a variety of infections. Doxycycline is a semisynthetic tetracycline invented and clinically developed in the early 1960s by Pfizer Inc. and marketed under the brand name Vibramycin. Vibramycin...

 twice daily is the combination most often used, and appears to be efficacious; the advantage of this regimen is that it is oral medication and there are no injections; however, a high rate of side effects (nausea, vomiting, loss of appetite) has also been reported.

Human brucellosis

Sir David Bruce
David Bruce (microbiologist)
Major-General Sir David Bruce KCB FRS FRSE was a Scottish pathologist and microbiologist who investigated the Malta-fever and trypanosomes, identifying the cause of sleeping sickness....

 isolated B. melitensis from British soldiers who died from Malta fever in Malta
Malta
Malta , officially known as the Republic of Malta , is a Southern European country consisting of an archipelago situated in the centre of the Mediterranean, south of Sicily, east of Tunisia and north of Libya, with Gibraltar to the west and Alexandria to the east.Malta covers just over in...

. The disease is characterized by acute undulating fever, headache, night sweats, fatigue and anorexia
Anorexia (symptom)
Anorexia is the decreased sensation of appetite...

. Human brucellosis is not considered a contagious disease and people become infected by contact with fluids from infected animals (sheep, cattle or pigs) or derived food products like unpasteurized milk and cheese. Brucellosis is also considered an occupational disease because of a higher incidence in people working with animals (slaughterhouse cases). The real worldwide incidence of brucellosis is unknown because there is a low level of surveillance and reporting in Brucella endemic areas.

Blue light study

In a study published in Science
Science (journal)
Science is the academic journal of the American Association for the Advancement of Science and is one of the world's top scientific journals....

 in August 2007, it was revealed that Brucella reacts strongly to the presence of the blue spectrum in natural light, reproducing at a great rate and becoming infectious. Conversely, depriving Brucella of the blue wavelengths dropped its reproductive rate by 90%, a result one of the co-authors called "spectacular."

External links

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