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Legionella Plate 01.png
Legionella sp. under ultraviolet illumination
Scientific classification
Domain: Bacteria
Phylum: Proteobacteria
Class: Gammaproteobacteria
Families and genera


The Legionellales are an order of Proteobacteria. Like all Proteobacteria, they are Gram-negative. [1] They comprise two families, typified by Legionella and Coxiella , both of which include notable pathogens. For example, Q fever is caused by Coxiella burnetii and Legionella pneumophila causes Legionnaires' disease [2] [3] and Pontiac fever. [4] [5] [6]

Proteobacteria phylum of Gram-negative bacteria

Proteobacteria is a major phylum of gram-negative bacteria. They include a wide variety of pathogens, such as Escherichia, Salmonella, Vibrio, Helicobacter, Yersinia, Legionellales and many other notable genera. Others are free-living (non-parasitic) and include many of the bacteria responsible for nitrogen fixation.

<i>Legionella</i> genus of bacteria

The genus Legionella is a pathogenic group of Gram-negative bacteria that includes the species L. pneumophila, causing legionellosis including a pneumonia-type illness called Legionnaires' disease and a mild flu-like illness called Pontiac fever.

<i>Coxiella burnetii</i> species of bacterium

Coxiella burnetii is an obligate intracellular bacterial pathogen, and is the causative agent of Q fever. The genus Coxiella is morphologically similar to Rickettsia, but with a variety of genetic and physiological differences. C. burnetii is a small Gram-negative, coccobacillary bacterium that is highly resistant to environmental stresses such as high temperature, osmotic pressure, and ultraviolet light. These characteristics are attributed to a small cell variant form of the organism that is part of a biphasic developmental cycle, including a more metabolically and replicatively active large cell variant form. It can survive standard disinfectants, and is resistant to many other environmental changes like those presented in the phagolysosome.

Related Research Articles

Q fever disease caused by infection with Coxiella burnetii, a bacterium that affects humans and other animals; the most common manifestation is flu-like symptoms; the name Q stands for “query”, so named when the pathogen was unknown

Q fever is a disease caused by infection with Coxiella burnetii, a bacterium that affects humans and other animals. This organism is uncommon, but may be found in cattle, sheep, goats, and other domestic mammals, including cats and dogs. The infection results from inhalation of a spore-like small-cell variant, and from contact with the milk, urine, feces, vaginal mucus, or semen of infected animals. Rarely, the disease is tick-borne. The incubation period is 9–40 days. Humans are vulnerable to Q fever, and infection can result from even a few organisms. The bacterium is an obligate intracellular pathogenic parasite.

Pontiac fever is an acute, nonfatal respiratory disease caused by various species of Gram-negative bacteria in the genus Legionella. It causes a mild upper respiratory infection that resembles acute influenza. Pontiac fever resolves spontaneously and often goes undiagnosed. Both Pontiac fever and the more severe Legionnaire's disease are caused by the same bacteria, but Pontiac fever does not include pneumonia.

Atypical pneumonia, also known as walking pneumonia, is the type of pneumonia not caused by one of the pathogens most commonly associated with the disease. Its clinical presentation contrasts to that of "typical" pneumonia. A variety of microorganisms can cause it. When it develops independently from another disease it is called primary atypical pneumonia (PAP).

<i>Legionella pneumophila</i> species of bacterium

Legionella pneumophila is a thin, aerobic, pleomorphic, flagellated, non-spore-forming, Gram-negative bacterium of the genus Legionella. L. pneumophila is the primary human pathogenic bacterium in this group and is the causative agent of Legionnaires' disease, also known as legionellosis.

Kawasaki disease Human disease in which blood vessels throughout the body become inflamed

Kawasaki disease, also known as mucocutaneous lymph node syndrome, is a disease in which blood vessels throughout the body become inflamed. The most common symptoms include a fever that lasts for more than five days not affected by usual medications, large lymph nodes in the neck, a rash in the genital area, and red eyes, lips, palms or soles of the feet. Other symptoms include sore throat and diarrhea. Within three weeks of the onset of symptoms, the skin from the hands and feet may peel. Recovery then typically occurs. In some children, coronary artery aneurysms may form in the heart after 1–2 years.

Intracellular parasites are microparasites that are capable of growing and reproducing inside the cells of a host. Some parasites can cause disease.

Community-acquired pneumonia refers to pneumonia contracted by a person with little contact with the healthcare system. The chief difference between hospital-acquired pneumonia (HAP) and CAP is that patients with HAP live in long-term care facilities or have recently visited a hospital. CAP is common, affecting people of all ages, and its symptoms occur as a result of oxygen-absorbing areas of the lung (alveoli) filling with fluid. This inhibits lung function, causing dyspnea, fever, chest pains and cough.

Fever of unknown origin (FUO), refers to a condition in which the patient has an elevated temperature (fever) but despite investigations by a physician no explanation has been found.

Bartonella quintana, originally known as Rochalimaea quintana, and "Rickettsia quintana", is a micro-organism transmitted by the human body louse. This microorganism is the causative agent of the well known trench fever. This bacterium caused outbreaks of trench fever affecting 1 million soldiers in Europe during World War I.

Brugia timori is a human filarial parasitic nematode (roundworm) which causes the disease "Timor filariasis." While this disease was first described in 1965, the identity of Brugia timori as the causative agent was not known until 1977. In that same year, Anopheles barbirostris was shown to be its primary vector. There is no known animal reservoir host.

VZV globulin or VZV antibodies is an immune system medication that is used mostly for immunosuppressed patients who have been or may be exposed to the varicella zoster virus. It shortens the course of cutaneous disease and may protect against its dissemination. Varicella zoster virus is a human herpes virus that causes chickenpox, shingles, Ramsay Hunt syndrome type II, and postherpetic neuralgia. Unlike a Zoster vaccine which provides durable immunity, the protection is passive and short term; it may need to be readministered every 2-4 weeks as necessary. This medication is not recommended for administration to immune-competent persons for treatment of active disease.

1976 Philadelphia Legionnaires disease outbreak

The 1976 Legionnaires disease outbreak, occurring in the late summer in Philadelphia, Pennsylvania, was the first occasion in which a cluster of a particular type of pneumonia cases were determined to be caused by the Legionella pneumophila bacteria.

Legionella anisa is a Gram-negative bacterium, one of more than 40 species in the family Legionellaceae. After Legionella pneumophila, this species has been isolated most frequently from water samples. This species is also one of the several pathogenic forms of Legionella having been associated with rare clinical cases of illness including Pontiac fever and Legionnaires' disease.

Legionella cherrii is an aerobic, flagellated, Gram-negative bacterium from the genus Legionella. It was isolated from a heated water sample in Minnesota. L. cherrii is similar to another Legionella species, L. pneumophila, and is believed to cause major respiratory problems.

Legionella feeleii is a Gram-negative, rod-shaped bacterium from the genus Legionella which was isolated from an automobile plant and which was held responsible for causing Pontiac fever in 317 workers. The organism did not grow on blood agar, required L-cysteine, and showed significant quantities of branched-chain fatty acids. More recently, an unusual, extrapulmonary case was described in a 66-year-old woman admitted to Hopital Nord, Marseille, France because of a complicated cellulitis and an abscess on her right leg following a suspected insect or spider bite.

Legionella jordanis is a Gram-negative bacterium from the genus Legionella which was isolated from the Jordan River in Bloomington, Indiana and from the sewage in DeKalb County, Georgia. L. jordanis is a rare human pathogen and can cause respiratory tract infections.

Legionnaires disease legionellosis that is characterized by severe form of infection producing pneumonia. Symptoms include fever, chills, and cough.

Legionnaires' disease, also known as legionellosis, is a form of atypical pneumonia caused by any type of Legionella bacteria. Signs and symptoms include cough, shortness of breath, high fever, muscle pains, and headaches. Nausea, vomiting, and diarrhea may also occur. This often begins 2–10 days after exposure.


  1. George M. Garrity: Bergey's Manual of Systematic Bacteriology . 2. Auflage. Springer, New York, 2005, Volume 2: The Proteobacteria, Part B: The Gammaproteobacteria
  2. Fraser, D.W., Tsai, T,. Orenstein, W., et al. (1977). Legionnaires' disease: description of an epidemic of pneumonia. New England Journal of Medicine. 297:1189–1197.
  3. McDade, JE., Shepard, C.C., Fraser, D.W., et al., (1977) Legionnaires' Disease — Isolation of a Bacterium and Demonstration of Its Role in Other Respiratory Disease. New England Journal of Medicine. 297: 1197–1203.
  4. "General Information- Pontiac Fever". HPA. Retrieved 2013-04-07.
  5. http://jid.oxfordjournals.org/content/191/9/1530.full.pdf
  6. "Pontiac Fever Due to Legionella micdadei from a Whirlpool Spa: Possible Role of Bacterial Endotoxin". Jid.oxfordjournals.org. Retrieved 2013-04-07.