Mycoplasma characteristics, taxonomy, morphology, symptoms

Philip Kelley

Mycoplasma it is a bacterial genus made up of approximately 60 species. They are part of the normal flora of the mouth and can be isolated from saliva, oral mucosa, sputum, or normal tonsil tissue, especially M. hominis Y M. salivarius.

However, they are recognized pathogens of the human respiratory and urogenital tract and of the joints in animals. The most important species of this genus is Mycoplasma pneumoniae, responsible for 10% of pneumonia, and Mycoplasma hominis, causing postpartum fever in women and fallopian tube infections.

Mycoplasma pneumoniae

Mycoplasmas are the smallest bacteria that can live free in nature and self-replicate extracellularly, in addition to having DNA and RNA. All these characteristics differentiate them from viruses.

They pass through filters whose pore size is 450nm, and therefore in this respect they are comparable to Chlamydia and larger viruses. Despite their small size, they can grow in synthetic laboratory culture media.

Article index

  • 1 Features
    • 1.1 Nutritional characteristics
    • 1.2 Susceptibility to antibiotics
  • 2 Taxonomy
  • 3 Morphology
  • 4 Cultivation
  • 5 Virulence factors
  • 6 Pathologies
    • 6.1 Diseases in man
    • 6.2 Disease in animals
    • 6.3 Diseases in plants
  • 7 Diagnosis
  • 8 Treatment
  • 9 Epidemiology
  • 10 Immunity
  • 11 Prevention and control
  • 12 References


-Mycoplasmas can live saprophytically in inhospitable environments such as hot springs, mine drains, or parasitically on humans, animals, and plants..

-Mycoplasmas have an affinity for the membranes of mammalian cells.

-Some species of Mycoplasmas have been isolated from the genital, urinary, respiratory and mouth tracts, without causing any damage. But the species M. pneumoniae never found as normal microbiota.

-Its presence stimulates the formation of cold agglutinins, nonspecific antibodies that agglutinate human erythrocytes when cold. These antibodies help the diagnosis, since they are elevated in convalescence.

Nutritional characteristics

Mycoplasmas use glucose as an energy source and need a microaerophilic environment (5% COtwo) to grow. Likewise, it is essential that the culture media contain sterol, purines and pyrimidines so that they can develop.

They grow very slowly and it may take up to 3 weeks for colonies to appear..

Mycoplasma pneumoniae it is strictly aerobic but the other species are facultative anaerobes.

Susceptibility to antibiotics

This genus is resistant to all beta-lactam antibiotics and glycopeptides, since they act at the cell wall level and these microorganisms lack this structure.

But if they are inhibited by tetracycline and erythromycin.


Domain: Bacteria,

Phylum: Firmicutes,

Class Mollicutes,

Order: Mycoplasmatales,

Family: Mycoplasmataceae,

Genus: Mycoplasma.


-Their size ranges from 125 to 300 nm, they are pleomorphic, that is, they can take different forms.

-They lack a rigid cell wall, their cytoplasm being limited by a trilaminar cell membrane containing sterol. For this reason, they do not stain with the Gram stain, staining slightly with Giensa.

-It has a very small double-stranded genomic DNA.


On solid culture media, colonies are characteristically embedded below the surface. These colonies are plastic protoplasmic masses of indefinite shape that are easily deformed.

Growth in liquid media produces many different shapes, including rings, bacillary, spherical, pyriform, filamentous, and stellate bodies. They grow in special PPLO (Pleuropneumonia Like Organism) media at 37 ° C for 48 to 96 hours or more.

After this time, tiny isolated round colonies measuring 20 to 500 µm can be observed with a magnifying glass..

Colonies of some Mycoplasmas species have a grainy surface with a dense center typically buried in agar (inverted fried egg appearance).

Virulence factors

Little is known about these microorganisms in this regard, but the presence of adhesins has been observed in the cytoplasmic membrane, which are proteins that bind to a receptor on the cells of the affected tissues..


Diseases in man


They can be caused by M. hominis.


It can be caused by Mycoplasma genitalium.

Pelvic inflammatory disease and vaginitis

Produced by Mycoplasma hominis. If it is not treated in time it can cause infertility.

Puerperal fever

Postpartum fever caused mainly by M. hominis.


Mycoplasma pneumoniae It is the main cause of pneumonia, especially in ages 5 to 20 years. The infection can go unnoticed (asymptomatic), be mild, or severe. It can also affect the ear causing otitis media or bullous myringitis..

This type of pneumonia is called atypical pneumonia because it does not respond to penicillin treatment and to differentiate it from pneumonia caused by Streptococcus pneumoniae.

Common symptoms include chest pain, sore throat, fever, chills, sweating, or a dry cough..

There may be complications such as earache, muscle and joint pain, skin rashes, among others..

Disease in animals

Animals can be affected by these microorganisms. Bovine pleuropneumonia (pneumonia and pleural effusion) has been seen which can cause the death of the animal. The disease spreads through the air.

Sheep and goat agalactia has been observed in the Mediterranean region. This infection is characterized by local lesions of the skin, eyes, joints, udder and scrotum, causing atrophy of the lactating breasts in females..

The microorganism is isolated from the blood, milk and exudates of the animal. In poultry, microorganisms cause various respiratory diseases that cause serious financial problems. The bacteria are transmitted from the hen to the egg and to the chicken.

In general, Mycoplasma can cause infections that particularly affect the pleura, peritoneum, joints, respiratory tract and eyes in animals such as pigs, rats, dogs, mice and other species..

Plant diseases

Mycoplasmas cause aster chlorosis, corn stunting, and other plant diseases. These diseases are transmitted by insects.


For the diagnosis of pneumonia due to Mycoplasma pneumoniae, first it is necessary to have the patient's medical history and physical examination.

Because Mycoplasmas grow very slowly in the laboratory, the diagnostic culture method is of little use. The sputum Gram does not help much either, because the microorganism will not be visible in it..

The diagnosis is usually based on serology, determination of specific IgM antibodies and the presence of cold agglutinins, capable of cold agglutinating human red blood cells of group "O".

However, although the elevation of these agglutinins suggests infection by Mycoplasma pneumoniae, It is not confirmatory, since these can appear in other infections due to adenovirus, influenza and mononucleosis.

Other more sophisticated and not routinely used diagnostic methods are immunoassays, DNA hybridization, and polymerase chain reaction (PCR)..

Other complementary tests may be chest X-ray and arterial blood gas..

In the case of Mycoplasma genitalium, does not grow in the usual media for Mycoplasmas, so its diagnosis is made only by molecular methods.


Depending on the severity of the disease, treatment can be oral outpatient or intravenous with a requirement for hospitalization. Tetracycline or any of the macrolides (azithromycin, clarithromycin, or erythromycin) is generally used.

Quinolones have also shown efficacy. Clindamycin is not helpful.

It should be clear that beta-lactams and glycopeptides cannot be used to treat this genus, since these antibiotics attack the cell wall and this structure is absent in Mycoplasmas..

The antibiotics that intervene in the synthesis of folic acid are not useful either..

It is recommended to drink a lot of water and fluids in general to help the phlegm and pulmonary secretions are eliminated in the case of respiratory infections caused by Mycoplasma pneumoniae.

The prognosis is good in most cases and recovery is faster after medical treatment..

In the case of M. hominis  it must be taken into account that this microorganism is resistant to erythromycin.


The main species of the genus Mycoplasma is the pneumoniae species and its only reservoir is man. The mode of transmission is through droplets of saliva from an infected person expelled by talking, coughing or sneezing, with or without symptoms..

It is said that the affected person can transmit the infection, from two to eight days before the symptoms appear, up to 14 weeks after recovery, so it is considered to be moderately contagious.

The inoculum for transmission is very low, approximately 100 CFU or perhaps less.

Infections by Mycoplasma pneumoniae occur throughout the world, but predominate in temperate climates, characterized by being sporadic and endemic.

It is common for it to spread in closed spaces, for example in members of the same family, in institutions, residences, etc., mainly affecting children and young adults.

Mycoplasma hominis can be present in the genitourinary tract in a carrier state in both men and women, mainly in promiscuous.

It is transmitted sexually and can affect the newborn during pregnancy or delivery..


Complement-fixing serum antibodies appear after Mycoplasma infection. They peak between 2 to 4 weeks after infection and gradually disappear after 6 to 12 months..

These antibodies play an important role in preventing reinfection, but for a certain time, so the infection can recur, since immunity is not permanent..

An immune response can also develop against the glycolipids of the outer membrane of Mycoplasmas..

This can be harmful as they mistakenly attack human erythrocytes, causing hemolytic anemia and jaundice, which can occur in approximately two-thirds of symptomatic patients with pneumonia due to M. pneumoniae.

Due to the fact that it has been observed that the infection can be more intense in patients with advanced age, it has suggested that the clinical manifestations of the disease are a consequence of the immune response rather than invasion by the bacteria.

Prevention and control

The only possible preventive measure is to avoid contact with patients with acute pneumonia in the case of Mycoplasma pneumoniae. Ideally, the patient should be isolated to reduce the likelihood of spread..

It is advisable to comply with hygiene measures, hand washing, sterilization of contaminated material, etc. Set aside utensils that may be of common use between the patient and their relatives, such as cutlery, glasses, etc..

Immunosuppressed patients should avoid going to closed places with crowds of people, such as cinemas, schools, among others.

In order to Mycoplasma hominis Y M. genitalium avoid having sex with promiscuous people.

In all the pathologies caused by the Mycoplasma genus, there may be people with asymptomatic infection, in these cases prevention is very difficult. So far there are no vaccines for this genus.


  1. Koneman E, Allen S, Janda W, Schreckenberger P, Winn W. (2004). Microbiological Diagnosis. (5th ed.). Argentina, Editorial Panamericana S.A.
  2. Ryan KJ, Ray C. (2010). SherrisMicrobiology Medical (6th edition) New York, U.S.A. McGraw-Hill Publishing House.
  3. Finegold S, Baron E. (1986). Bailey Scott Microbiological Diagnosis. (7 ma ed) Argentina Editorial Panamericana.
  4. Jawetz E, Melnick J, Adelberg E. (1992). Medical Microbiology. (14 ta Edition) Mexico, Editorial El Manual Moderno.
  5. Arnol M. Urogenital mycoplasmas as a cause of female infertility. Matanzas Provincial Gyneco-Obstetric Hospital. 2014-2015. Rev Méd Electron 2016; 38 (3): 370-382. Available at:
  6. Razin S. Mycoplasmas. In: Baron S, editor. Medical Microbiology. 4th edition. Galveston (TX): University of Texas Medical Branch at Galveston; 1996. Chapter 37. Available from:
  7. Kashyap S, Sarkar M. Mycoplasma pneumonia: Clinical features and management. Lung India: Official Organ of Indian Chest Society. 2010; 27 (2): 75-85. doi: 10.4103 / 0970-2113.63611.

Yet No Comments