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Introduction of Mycoplasma

A cell wall deficient organism was isolated by Nocard and Roux in 1998, from a cattle suffering from pleuropneumonia. The organism was filterable through bacteria stopping filter and highly pleomorphic. Because of their resemblance to the organisms responsible for pneumonia in the cattle, for many years this organism was called Pleuropneumonia-like organism (PPLO). Since organisms are seen like fungus in the form of branching filaments, the name given today for this organism is Mycoplasma.

Characteristics of Mycoplasma

• They do not have a rigid cell wall
• Size : 0.1-2 micron
• Contains a small unit of cytoplasm composed of a protein like a membrane
• The cytoplasm contains strands of DNA and ribosomes
• They are pleomorphic microorganisms and may appear as cocci or long filaments which may appear as branched.
• They are nonmotile.
• They are thought to reproduce by the coccal forms elongating and then forming new cocci which then become detached.
• Pathogenic organisms require sterols for their growth some also require urea. The urea requiring Mycoplasma form microscopic colonies on artificial media and is known as Tiny (T) Mycoplasma. These are classified as Ureaplasma species.  The T- Mycoplasma that does not require urea for their growth are included in the genus Mycoplasma.

The main species of medical  importance are :

• M.  pneumoniae
• M.  hominis
• Ureaplasma urealyticum

Normal Habitat

• Soil, plant, and mucus surface of the animal
• In humans, as a part of pathogens, M. hominins and Ureaplasma urealyticum are found in the lower genital tract, mouth, and throat.
• M. pneumoniae can be found in the respiratory tract.

Resistance

They are normally destroyed by heat at  45°C in 15 minutes.

They are relatively resistant to penicillins, and Cephalosporins.

They are sensitive to tetracyclines, and several other antibiotics.

Antigenic properties

• The surface antigens are glycolipids and proteins.
• Glycolipids are identified by complement fixation.
• Proteins antigens detected by ELISA method.

Pathogenicity of Mycoplasma

M. pneumoniae causes pneumonia, lower respiratory and upper respiratory tract infections including sore throat, inflammation of the ear.

Also stimulates the production of cold agglutinin autoimmunity.

M. hominis causes the following diseases-

• Pelvic inflammatory disease (PID)
• Pyelonephritis
• Spontaneous abortion
• Postpartum fever

Ureaplasma urealyticum causes

• Non – gonococcal urethritis in men
• PID

Clinical Manifestations

• Generalized aches and pains
• Fever (usually 102°F)
•  Cough – Usually non-productive
• Sore throat (non-exudative pharyngitis)
• Headache/ myalgias
• Chills but not rigors
•  Nasal congestion with coryza
• Earache
• General malaise

Laboratory diagnosis of Mycoplasma

Collection of samples: Samples are collected as per the site of infection

Microscopy

Mycoplasma can not be detected directly in the stained preparation. Therefore, culture is required.

Culture

• Media: Pleuropneumonia (PPLO) agar and
• PPLO biphasic medium ( broth/ agar)
• These media are supplemented with 20 % horse serum, yeast extract, and DNA.
• After inoculation of the specimen, incubate at 37°C in the presence of CO₂ for 7 -12 days.

Colony characteristic

Typical tiny fried egg appearance colonies are formed on the surface of the agar of the medium. The colonies should be studied with the help of a hand lens or under a stereomicroscope.

Staining of colonies

A small block of agar containing one or two colonies can be cut and put on the slide then stain with Dienes stain (Methylene and azure). The colony will take the royal intense blue color.

Subculture is done by rubbing the agar block containing Mycoplasma into new PPLO agar.

Biochemical  properties of different Mycoplasma

Thallium                      Tetrazolium                  Phosphatase          Urea

Sensitive                   reduction                     activity                        hydrolyses

M. pneumoniae      R          +                    –                               –

M.  hominis             S            –                    –                                –

U. urealyticum       S            –                   +                                –

Serological diagnosis of M. pneumoniae

1. Complement Fixation Test
2. Fourfold in titer in paired sera has diagnostic value
3. Cold agglutinin
4. 33-76% of patients with M. pneumoniae infection produce IgM autoantibodies that agglutinate their own red blood cells and other human red blood cells (Group O Rhesus negative ) at 4°C.

Mycoplasma is found in the oropharynx as a part of normal flora

• M. orale
• M.  salvarium
• M.  buccale
• M. faucium

Mycoplasma is found in the Genital tract as part of normal flora

• M. fermentans
• M. primatum

Treatment

Drugs used in Mycoplasma infections are as follows-

• Erythromycin (M. pneumoniae and  Ureaplasma spp.)
• Tetracyclines
• Clindamycin (M. hominis)
•  Levofloxacin
• Doxycycline
• Gentamycin

Key Notes

1. Mycoplasma is a cell wall deficient microorganism.
2. They differ from viruses in following ways-

• They grow on cell-free media in vitro.
• They contain both  RNA and DNA.
• They have both intracellular as well as extracellular parasitism in vivo.

References

1. https://www.ncbi.nlm.nih.gov/books/NBK7637
2. https://www.ncbi.nlm.nih.gov/pmc/articles/PMC2893430/
3. https://academic.oup.com/femsre/article/32/6/956/2683353
4. https://www.sciencedirect.com/science/article/pii/S1198743X14631141
5. https://en.wikipedia.org/wiki/Mycoplasma
6. https://www.cdc.gov/pneumonia/atypical/mycoplasma/hcp/disease-specifics.html
7. https://bestpractice.bmj.com/topics/en-us/605
8. https://www.hindawi.com/journals/tswj/2014/549858/
9. https://cmr.asm.org/content/17/4/697