Mycoplasma: Introduction, Morphology and Biochemical Reactions

Introduction

  • Smallest micro organisms
  • Free living in nature
  • Can grow in cell free medium
  • Causes human infection
  1. M. pneumoniae: Pneumonia
  2. Ureaplasma urealyticum: non-gonococcal urethritis
  3. M. hominis and M. gentalium: genital tract infections.
  • Cell wall absent
  • Highly pleomorphic in nature
  • Has no fixed shape and size
  • Absence of cell wall precursors that are
  1. Muramic acid
  2. diaminopimelic acid
  • Soft tri-laminar unit membrane present, bound to the cells.
  • Such membrane made up of sterols.
  • Shows plasticity that enables them to pass through bacterial filters.
  • Mistakenly taken as viruses.
  • Nocard and Roux (1898) identified the first member of this group.
  • Isolated from bovine pleuro-pneumonia.
  • Also, similar organism isolated from contagious agalactia in sheep.
  • Similar isolates identified form different organisms and environmental sources.
  • Thus called, pleuropneumoia-like organisms (PPLO).
  • Later replaced by the term mycoplasma.
  • Myco: means fungus like branching filaments,
  • Whereas, plasma signifies plasticity of shape.

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Morphology

  • Easily passes through filters of pore size 450 nm.
  • Presence is seen in granular form.
  • Also found in filaments form that varies in sizes.

Granules: coccoid, balloon, ring or star, disc forms.

Filaments: slender, of different length, true branched.

  • Multiplies through binary fission
  • Genomic replication and cell division are often asynchronous.
  • Appears as budding forms or chains of beads.
  • Bulbous enlargement with differentiated tip structure in some species.
  • Thus, helps in adherence to the host cells having neuraminic acid receptors.
  • In some species, also responsible for hemadsorption.
  • Non-sporing, non-flagellated or non fimbriated.
  • Though Gram negative, better stained by Giemsa stain.
  • Some species shows gliding motility.

Cultural characteristics

  • Fluid or solid media required for cultivation.
  • Facultative anaerobes though better growth in aerobic condition.
  • Temperature requirement
  1. 22-41°C: Temperature range for growth
  2. 35-37°C: Optimum growth for parasitic species
  3. Lower temperatures: Saprophytic species
  • Enriched media used for cultivation
  1. 20% horse or human serum
  2. Yeast extract
  • Selective agents used are
  1. Penicillin
  2. Thallium acetate
  • High concentration serum required.
  • Fulfills cholesterol and other lipids requirements.
  • 2-6 days incubation required for colonies to appear.
  • Colonies characteristics
  1. 10-600 µm size
  2. -Typically biphasic
  3. Fried egg appearance
  4. -An opaque granular area located centrally
  5. -Extends into the depth of the medium
  6. -This area surrounded by a flat translucent peripheral zone
  7. -Hand lens can be used to observe colonies
  8. -Staining by Dienes method required for study of colonies

Mycoplasma: Introduction, Characteristics, Pathogenecity, Lab Diagnosis

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Dienes method of staining

Following steps are involved in this method of staining.

  • Firstly, a block of agar containing colony is cut.
  • After it, the block with the colony is placed on the slide.
  • Now, cover this slide containing colonies with a cover slip.
  • The coverslip used is firstly treated with alcoholic solution of methylene blue and azure and then dried.
  • Since, Loops cannot pick up the colonies due to its small size.
  • Thus, subculture is carried out by rubbing the cut colonies along with the agar block in the fresh plate.
  • In liquid medium
  1. -No turbidity appreciated
  2. -Pleomorphic forms are found

Biochemical reactions

  • Chemo-organotrophs
  • Metabolism: Fermentative
  • Source of energy: glucose or arginine(most species)
  • Urea hydrolysis: negative (except Ureaplasmas)
  • Non-proteolytic
  • Cholesterol and related sterols incorporated in their surface membranes
  • Purines and pyrimidines synthesis absent

Resistance

  • Heat resistance similar to non-sporing bacteria.
  • Some strains are more sensitive
  • Destroys: exposure to 45°Celsius for 15 minutes.
  • Resist: osmolytic shock related lysis.
  • Sensitive towards:
  1. surface active agents related lysis.
  2. lipolytic agents such as taurocholate and digitonin.
  3. tetracycline and many other antibiotics
  • Resistance against:
  1. Penicillin and cephalosporin
  2. Lysozymes acting on bacterial cell wall
  • Susceptible towards erythromycin.
  • Gold salt: growth inhibition
  • Some macrolide antibiotics: differentiation of species
  • 002% methylene blue:
  1. different species inhibited
  2. M. pneumoniae can grow

Antigenic properties

  • Serological tests used are:
  1. Agglutination
  2. Passive haem-agglutination
  3. Complement fixation
  4. ELISA
  5. Immunoflurescence
  • These tests are performed to identify isolates by detecting antibodies in sera.
  • Antigens present are generally surface antigens.
  1. Mainly glycolipids: identified by complement fixation test
  2. Proteins: identified by ELISA
  • “Growth inhibition test” also helps in identification of the isolates
  • It is based on the antisera ability to inhibit the growth of homologous species on solid media specifically.

References: 

i) https://www.healthline.com/health/mycoplasma-pneumonia

ii) https://www.ncbi.nlm.nih.gov/books/NBK7637/

Mycoplasma: Introduction, Morphology and Biochemical Reactions

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