Mycoplasma pneumoniae
Mycoplasma pneumoniae is a very small bacterium in the class Mollicutes
The Mollicutes are a class of bacteria distinguished by the absence of a cell wall. The word "Mollicutes" is derived from the Latin mollis , and cutis . They are parasites of various animals and plants, living on or in the host's cells. Individuals are very small, typically only 0.2–0.3 μm in size...

It causes the disease mycoplasma pneumonia
Mycoplasma pneumonia
Mycoplasma pneumonia is a form of bacterial pneumonia which is caused by the bacteria species Mycoplasma pneumoniae....

, a form of atypical
Atypical pneumonia
Atypical pneumonia aka "walking pneumonia" is a pneumonia not caused by one of the more traditional pathogens, and with a clinical presentation inconsistent with typical pneumonia. It can be caused by a variety of microorganisms...

Bacterial pneumonia
Bacterial pneumonia is a type of pneumonia caused by bacterial infection.-Sign and symptoms:*Fever*Rigors*Cough*Dyspnea*Chest pain*Pneumococcal pneumonia can cause Hemoptysis-Gram positive:...

Pneumonia is an inflammatory condition of the lung—especially affecting the microscopic air sacs —associated with fever, chest symptoms, and a lack of air space on a chest X-ray. Pneumonia is typically caused by an infection but there are a number of other causes...

, and is related to cold agglutinin disease.

Cell wall/Treatment

This species lacks a peptidoglycan
Peptidoglycan, also known as murein, is a polymer consisting of sugars and amino acids that forms a mesh-like layer outside the plasma membrane of bacteria , forming the cell wall. The sugar component consists of alternating residues of β- linked N-acetylglucosamine and N-acetylmuramic acid...

 cell wall
Cell wall
The cell wall is the tough, usually flexible but sometimes fairly rigid layer that surrounds some types of cells. It is located outside the cell membrane and provides these cells with structural support and protection, and also acts as a filtering mechanism. A major function of the cell wall is to...

, like all Mollicutes. Instead, it has a cell membrane
Cell membrane
The cell membrane or plasma membrane is a biological membrane that separates the interior of all cells from the outside environment. The cell membrane is selectively permeable to ions and organic molecules and controls the movement of substances in and out of cells. It basically protects the cell...

 that incorporates sterol
Sterols, also known as steroid alcohols, are a subgroup of the steroids and an important class of organic molecules. They occur naturally in plants, animals, and fungi, with the most familiar type of animal sterol being cholesterol...

 compounds, similar to eukaryotic cell
A eukaryote is an organism whose cells contain complex structures enclosed within membranes. Eukaryotes may more formally be referred to as the taxon Eukarya or Eukaryota. The defining membrane-bound structure that sets eukaryotic cells apart from prokaryotic cells is the nucleus, or nuclear...

s. It obtains these sterols from the host serum, allowing it to retain a simple structure. Lacking a cell wall
Cell wall
The cell wall is the tough, usually flexible but sometimes fairly rigid layer that surrounds some types of cells. It is located outside the cell membrane and provides these cells with structural support and protection, and also acts as a filtering mechanism. A major function of the cell wall is to...

, these organisms are resistant to the effects of penicillin
Penicillin is a group of antibiotics derived from Penicillium fungi. They include penicillin G, procaine penicillin, benzathine penicillin, and penicillin V....

s and other beta-lactam antibiotics, which act by disrupting the bacterial cell wall. Antibiotics with activity against these organisms include certain macrolides (erythromycin
Erythromycin is a macrolide antibiotic that has an antimicrobial spectrum similar to or slightly wider than that of penicillin, and is often used for people who have an allergy to penicillins. For respiratory tract infections, it has better coverage of atypical organisms, including mycoplasma and...

, azithromycin
Azithromycin is an azalide, a subclass of macrolide antibiotics. Azithromycin is one of the world's best-selling antibiotics...

, clarithromycin
Clarithromycin is a macrolide antibiotic used to treat pharyngitis, tonsillitis, acute maxillary sinusitis, acute bacterial exacerbation of chronic bronchitis, pneumonia , skin and skin structure infections...

), fluoroquinolones and their derivatives (e.g., ciprofloxacin
Ciprofloxacin is a synthetic chemotherapeutic antibiotic of the fluoroquinolone drug class.It is a second-generation fluoroquinolone antibacterial. It kills bacteria by interfering with the enzymes that cause DNA to rewind after being copied, which stops synthesis of DNA and of...

, levofloxacin
Levofloxacin is a synthetic chemotherapeutic antibiotic of the fluoroquinolone drug class and is used to treat severe or life-threatening bacterial infections or bacterial infections that have failed to respond to other antibiotic classes. It is sold under various brand names, such as Levaquin and...

), and tetracyclines (e.g., 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...

). The outer most boundary is three layered plasma membrane called trilaminar unit membrane.


M. pneumoniae has one of the smallest genome
In modern molecular biology and genetics, the genome is the entirety of an organism's hereditary information. It is encoded either in DNA or, for many types of virus, in RNA. The genome includes both the genes and the non-coding sequences of the DNA/RNA....

s known, with 816 kilobase pairs
Base pair
In molecular biology and genetics, the linking between two nitrogenous bases on opposite complementary DNA or certain types of RNA strands that are connected via hydrogen bonds is called a base pair...

 (kbs). Its genome and proteome
The proteome is the entire set of proteins expressed by a genome, cell, tissue or organism. More specifically, it is the set of expressed proteins in a given type of cells or an organism at a given time under defined conditions. The term is a portmanteau of proteins and genome.The term has been...

 have been fully characterized. It uses some unique genetic code, making its code more similar to mitochondria than to other bacteria. Thus it is said that Mycoplasma pneumoniae has a degenerate genome. It lacks the cellular machinery for making many essential compounds, including new purines and pyrimidines. It also has no tri-carboxylic acid cycle and an incomplete electron transport chain
Electron transport chain
An electron transport chain couples electron transfer between an electron donor and an electron acceptor with the transfer of H+ ions across a membrane. The resulting electrochemical proton gradient is used to generate chemical energy in the form of adenosine triphosphate...

. Because of this, it is an obligate parasite
Obligate parasite
An obligate parasite is a parasitic organism that cannot complete its life cycle without dependence on its host.-See also:*Obligate intracellular parasite*Parasitism*Parasitic plant*Facultative parasite...

 and is never found free-living.


M. pneumoniae was historically known as "Eaton's agent."

First M. pneumoniae was considered as a virus rather than a bacterium, when Eaton and colleagues cultured the causative agent of human primary atypical pneumonia (PAP) or "walking pneumonia." This agent could be grown in chicken embryos and passed through a filter that excluded normal bacteria. However, it could not be observed by high magnification light microscopy, and it caused a pneumonia that could not be treated with the antimicrobial
An anti-microbial is a substance that kills or inhibits the growth of microorganisms such as bacteria, fungi, or protozoans. Antimicrobial drugs either kill microbes or prevent the growth of microbes...

s sulphonamides
Sulfonamide (medicine)
Sulfonamide or sulphonamide is the basis of several groups of drugs. The original antibacterial sulfonamides are synthetic antimicrobial agents that contain the sulfonamide group. Some sulfonamides are also devoid of antibacterial activity, e.g., the anticonvulsant sultiame...

 and penicillin
Penicillin is a group of antibiotics derived from Penicillium fungi. They include penicillin G, procaine penicillin, benzathine penicillin, and penicillin V....

. Eaton suggested the possibility that the disease was caused by a mycoplasma, but the agent did not grow on the standard PPLO media of the time. These observations led to the conclusion that the causative agent of PAP is a virus. Researchers at that time showed that the cultured agent could induce disease in experimentally infected cotton rats and hamsters. In spite of controversy whether the researchers had truly isolated the causative agent of PAP (based largely on the unusual immunological response of patients with PAP), in retrospect their evidence along with that of colleagues and competitors appears to have been quite conclusive. There were reports linking Eaton's Agent to the PPLOs or mycoplasmas, well known then as parasites of cattle and rodents, due to sensitivity to antimicrobial compounds (e.g., organic gold salt).

In the early 1960s, Leonard Hayflick
Leonard Hayflick
Leonard Hayflick , Ph.D., is Professor of Anatomy at the University of California, San Francisco, School of Medicine, and was Professor of Medical Microbiology at Stanford University School of Medicine. He is a past president of the Gerontological Society of America and was a founding member of the...

, then at the Wistar Institute
Wistar Institute
The Wistar Institute is a biomedical center, with a focus on cancer research and vaccine development. It is located in the University City section of Philadelphia, Pa...

in Philadelphia, was first to isolate and cultivate the causative agent of primary atypical pneumonia (the Eaton Agent). He identified the agent as a mycoplasma and named it Mycoplasma pneumoniae. The ability to grow Eaton's agent, now known as Mycoplasma pneumoniae, in cell-free media allowed an explosion of research into what had overnight become the most medically important mycoplasma and what was to become the most studied mycoplasma.

External links

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