Mycoplasma pneumoniae - Classification, Morphology, Culture, Biochemical test, Antigen

Classification of Mycoplasma pneumoniae

Mycoplasma pneumoniae can be classified as:

Domain: Bacteria

Phylum: Mycoplasmatota

Class: Mollicutes

Order: Mycoplasmatales

Family: Mycoplasmataceae

Genus: Mycoplasma

Species: pneumoniae

Characteristics of Mycoplasma pneumoniae

Mycoplasma pneumoniae causes respiratory tract diseases. It is known for causing primary atypical pneumonia or walking pneumonia. It can also cause pericarditis, hemolytic anemia, arthritis, nephritis, Bell’s palsy, and meningoencephalitis.

The multiplication takes place by binary fission.

Morphology of Mycoplasma pneumoniae

Mycoplasma pneumoniae are small (0.3 x 0.8 μm) / 150-250 nm and lack a cell wall and cell membrane containing sterols. It shows both intracellular and extracellular parasitism in vivo. The bacterium is pleomorphic and occurs as granular and filamentous and multiplication takes place by binary fission.

Mycoplasma pneumoniae do not contain flagella or pili- buts show gliding motility. Also, the bacterium stains poorly by gram stain and is gram-negative. They are better stained by Giemsa and Diene stains.

Culture

Mycoplasma pneumoniae is a strict aerobe that can be cultured at 37°C at pH 7.3-7.8.

PPLO broth (Pleuropneumonia like organism broth)

PPLO is the medium used for the isolation of mycoplasma species such as Mycoplasma pneumoniae. It contains 20% horse serum, 10% yeast extract, and glucose. Animal serum (in high concentration) can be used as the source of exogenous sterols (cholesterol and other lipids).

Phenol red is used as a pH indicator. Penicillin, ampicillin, and polymyxin B inhibit growth-contaminating bacteria while amphotericin B inhibits fungal growth.

PPLO agar

The addition of agar to PPLO broth gives agar Mycoplasma pneumoniae are slow grower with a generation time of 1-6 hours. On PPLO agar, Mycoplasma produces a small, fried egg colony consisting of a central, opaque, granular area of growth surrounded by a flat, translucent, peripheral area.

But Mycoplasma pneumoniae does not produce fried egg colonies. Its colonies are mulberry-shaped. After staining by Diene’s method, the fried egg colony of Mycoplams appears highly granular with the center of the colonies stained dark blue and the periphery of the colony stained light blue.

Since they are slow growers, they require 1-4 weeks to produce colonies on agar. Most Mycoplasms produce a zone of hemolysis on BA. Do not have the ability to synthesize cholesterol and related sterols and thus need supply from outside for growth. They also lack the ability to synthesize purines and pyrimidines.

Biochemical reaction of Mycoplasma

The biochemical reactions of Mycoplasma spp. are as follows:

• Mycoplasma pneumoniae, Mycoplasma fermentans, Mycoplasma genitalium, Mycoplasma agalactiae – utilize glucose and other carbohydrates as the major source of energy; also utilizes arginine

• Mycoplasma salivarium, Mycoplasma orale, Mycoplasma hominis, Mycoplasma fementans – utilize arginine as the major source of energy

• They are chemo-organotrophs and metabolism is fermentative while other species may be non-fermentative

• requires cholesterol and other sterols as growth factors

Antigenic properties, cell wall components of Mycoplasma pneumoniae

Membrane glycolipids and proteins are the major Antigenic determinants of Mycoplasma pneumoniae. Membrane glycolipids have a similar antigenic structure in neurons in the human brain, So, cross-reaction with human tissues and other bacteria occurs causing damage to neuronal cells

Mycoplasma pneumoniae possesses two major surface proteins. Adhesion protein P1 is responsible for the attachment of bacteria to cell structures. P1 protein induces the production of Ab which also reacts with Antigenic determinants of RBCs, leading to the lysis of erythrocytes in the autoimmune disease process. This protein antigen is identified by ELISA.