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Mycoplasma

College of Medicine

Dep. of Microbiology

Assist. Proph. Dr. Ilham alsaedi

Mycoplasma

There are over 150 species in the class of cell wall free bacteria. At least 15 of these species are thought to be human origin, while others have been isolated from animals and plants.

In Human, Four species are of primary importance:

1-Mycoplasma pneumonia

Cause pneumonia and has been associated with joint and other infections.

2-Mycoplasma hominis

Sometimes causes postpartum fever and has been found with other bacteria in uterine tube infections.

3-Ureaplasma urealyticum

Is causes of nongonococcal urethritis in men and is associated with lung disease in premature of low birth weight.

4-Mycoplasma genitalium

Is closely related to M. pneumoniae and has been associated with urethral and other infections.

Important characteristics:-

1-       The smallest mycoplasmas are 125-250 nm in size.

2-       They are highly pleomorphic because they lack a rigid cell wall.

3-       They are completely resistant to penicillin because they lack the cell wall structures where penicillin acts. but they are inhibited by tetracycline or erythromycin.

4-       The cell membrane contain cholesterol and other sterol (that found in Eukaryotic cell membrane).

5-       They can reproduce in cell free media.

6-       They have an affinity for mammalian cell membrane

7-       They were firstly called(PPLO) plauropneumoniae like organism.

*Its gram negative smallest pleomorphic free living organism which is non motile, varying in shape from spherical to branching filaments. Its facultative anaerobes growing better aerobically, pathogenic strain grows optimally at 35-37°C

Virulence factors and pathogenesis:-

     The mechanism of infection is less well understood but may include several factors as follows:

1-Attachment factors: May pathogenic Mycoplasma have specialized polar tip structures(terminal protein attachment factors) that mediate adherence to host epithelial cells of respiratory mucosa tissue.

Surface protein adhesion binds the organism to receptor (sialoglycolipids or neuramic acid glycoproteins) on respiratory epithelial cells.

2-Some pathogenic Mycoplasma produce peroxide and hemolytic RBCs. Direct cytotoxicity through generation of hydrogen peroxide and superoxide radicals, and cytolysis mediated by antigen-antibody reaction associated with pathogenesis.

Transmission and Epidemiology

      Transmission of M. pneumoniae is from person to person by airborne route (respiratory droplets).

It is generally shed into URT for 2-4days before overt symptoms of disease are seen. Shedding may continue for as long as 14 days.

Other Mycoplasma  and Ureaplasma can be transmitted by sexual contact.

M. pneumoniae infections occur worldwide, with an increased incidence in the winter. Most frequent of pneumonia in young adults and is responsible for outbreaks in groups with close contact such as families, military personals, and college students.

M pneumonia is responsible for pneumonia epidemics every 4-8 years in both civilian and military populations.

Pathogenicity and clinical findings:

 ((Infection of Humans))

Mycoplasma have been cultivated from human mucous membranes and tissues, particularly from the genital, urinary, and respiratory tracts. Mycoplasma are part of the normal flora of the mouth and can be grown from normal saliva, oral mucous membranes, sputum, or tonsillar tissue.

M.salivarium, M.orale can be recovered from the oral cavities of many healthy adults, but an associated with clinical disease is uncertain.

M. hominis is found in the oropharynx of less than 5% of adults.

Infections of human urogenital tract are caused by M. hominis and U.urealyticum is found in the urethra of some men with non gonococcal urethritis. Such infection may play a role in male infertility.

M. pneumoniae the organism cause a RTI the disease is less severe than other form of bacterial pneumonia.

Mycoplasma pneumonia:

    Acute non bacterial pneumonia (pneumonitis) may be due to many infectious agents including Adenoviruses, Influenza viruses, Para influenza viruses, Chlamydia and Coxiellaburnetii (the causative agent of Q-fever)but the single most prominent causative agent is M. pneumoniae especially in persons of 5-15 years.

The incubation period from 1-3 weeks, fever ,headache ,sore throat ,cough with hemolytic anemia and a variety of skin lesions. Later there may be blood streaked sputum and chest pain.Death is very rare and is usually attributed to cardiac failure.

Lab. Diagnosis:

A-     Speciemens: Throat swabs, sputum, inflammatory exudates and respiratory, urethral or genital secretions.

B-      Microscopic examination: Is useless because Mycoplasma stain poorly with gram stain.

C-      Culture: The specimens are inoculated on the solid media and incubated for 3-10 days at 37C°with 5% CO2.

D-     Serology: Antibodies develop in humans infected with Mycoplasma and can be demonstrated by several methods: complement fixation(CF) test can be performed with glycolipid antigens.

HI (Haemagglutination Inhibition test) can be applied to tanned RBCs with adsorbed Mycoplasma antigens.

Control on infection:

a-       Treatment: drug of choice is either Erythromycin or Tetracycline.

b-       There is no vaccine.