Mollicutes

Classification

What one commonly calls Mycoplasme gathers of the bacteria belonging to division 3 of the Tenericutes ( tener cuti-reactions means “tender skin”) reign of the Procaryota . Of the Mollicutes includes/understands the S Acholeplasmatales, Anaeroplasmatales, Entomoplasmatales, Mycoplasmatales.

Of the Mycoplasmataceae , which has an interest in human Médecine and veterinary, includes/understands two S:

the kind Mycoplasma with more than 100 S;
the kind Ureaplasma with 6 species.

They are very small Procaryote S (0,3 µm). They are equipped with a very small genome (including between 600 and 2200k Pb according to the species) and with a Coefficient of Chargaff (percentage G + C) low, ranging between 23% and 39%.

Evolution

Mycoplasmes are descendants of a primitive bacterium which would have existed before the development of the Peptidoglycane or they would be only degenerated forms of Eubactéries which would have lost their wall? The assumption currently retained according to the study of the sequences of ribosomal ARN 16S is that on the contrary the mycoplasmes are very advanced forms, derived of bacteria with positive Gram with low content guanine + cytosine. The mycoplasmes would have evolved/moved starting from these ancestors (certainly starting from bacteria of the kind Clostridium ) by a process including/understanding of the successive reductions of the size of the Génome and a loss of the wall. Clostridium innocuum and C. ramosum is the species nearest phylogenetically.

Bacteriological characters

The class of Mollicutes gathers procaryotic organizations deprived of wall and incompetents to synthesize the Peptidoglycane. They are thus polymorphic micro-organisms (spherical or pyriforme with the helicoid, or ramified filament). They are generally motionless bacteria (but certain species can move by slip), with coloring negative Gram, optional anaerobe. Because they do not have a wall, the β-lactamines are ineffective. The absence of wall confers an osmotic sensitivity to them.

The culture can be done on inert medium but certain species push better on cellular cultures. The majority of the mycoplasmes have very strict nutritive requirements, they develop on mediums complex, rich, added with a strong concentration of serum. They generally require sterol or fatty-acids for the growth. On solid media they form very typical fried egg colonies “” with an opaque central zone and a wide peripheral zone. The mycoplasma have the Enzyme S necessary to the synthesis of their metabolites. They can degrade a large variety of sugars and amino-acids. Their metabolism uses Glucide S or Arginine in the case of Mycoplasma and the Urée in the case of Ureaplasma .

Habitats

The mollicutes are species parasite S, commensales or Saprophyte S of the plants, insects, ticks, animals and of the man. They cause named diseases " mycoplasmose". The habitat of the Mycoplasma is represented by the mucous surface of the respiratory or genital tract, the eyes, the glands mammaires, the articulations of the animals or the Man.

The mycoplasmes often contaminate the cellular cultures of laboratory and are difficult to detect and eliminate.

Mycoplasma mycoides is the agent responsible for Péripneumonie Contagieuse Bovine (PPCB).

Mycoplasma hominis is a parasite of the genital ways of the man and the woman (sexually transmitted disease).

Mycoplasma pneumoniae causes respiratory infections.

Mycoplasma agalactiae is one of the species responsible for the syndrome of the contagious agalaxie of the small Ruminants (goat, sheep).

Mycoplasma bovis is pathogenic at the bovines, person in charge of bronchopneumonies, otitis medias in calf and mammites in the cow.

Ureaplasma urealyticum is a parasite of the genital ways of the man and the woman.

The species of the kind Spiroplasma are parasites of the plants (cause yellowing) and/or pathogenic certain insects.

The species of the kind Entomoplasma are isolated from plants and insects.

The species of the kinds Anaeroplasma and Asteroplasma are isolated from the rumen of the bovines and the sheep.

The members of the kind Acholeplasma are isolated from the intestine of insects.

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