Positive Gram

The Bactérie S with positive Gram are highlighted by a technique of coloring called Coloration of Gram. The bacteria with gram positive appear mauve then with the Microscope. The technique of coloring rests on the characteristics membrane S and of wall of the bacterium. Coloring in Gram is a determining factor in the Taxinomie (classification) bacterial.

Principle of coloring of positive Gram

After fixing of the Bacterium S on a blade (two possible methods: fixing with the ethanol with 90° or by passage of the blade in the flame):

the blade is plunged in a first dye: the Purple of gentian (or a close product, the purple Crystal). The purple one of gentian is coloring powerful (Toxique and Cancérigène). It will cross the wall S and membrane S of the bacteria and to fix itself in their Cytoplasme S. Ainsi at this stage all the cells are coloured purple.
the blade is then treated with the Lugol's solution iodo-iodized in solution which is used as corrosive : it will reinforce purple gentian contained in the Cytoplasme of the bacteria.
One drives out then the purple one with a solution of ethanol to 90°. This stage is crucial because it determines which bacterium is negative Gram and which bacterium is gram positive . The principle is the following: the bacteria gram positive have a wall rich in Peptidoglycane, component which prevents alcohol from carrying purple gentian this one remaining in the cytoplasm. The bacterium is thus not faded (for more information, to see below the section Caractéristiques of the bacteria Gram-positive ).
the blade after being rinsed is briefly plunged in a second dye, the Fuchsine . All the bacteria coloured purple are known as " GRAM+" and those coloured pink are " GRAM - "

The blade is then recovered, rinsed and dried, then observed with the optical Microscope generally with the objective x100 + oil with immersion. The bacteria gram positive will appear purple. The observation of their colors is generally accompanied by structural descriptions (e.g. bacillus or hull).

Characteristics of positive the Gram bacteria

Description of the envelope

The bacteria positive Gram have a structure which is organized in three great parts: (of outside towards the interior)

the layer of Peptidoglycane
space periplasmic
the plasmic membrane

The layer of positive Peptidoglycane of the bacteria with gram is very thick contrary to that of the bacteria with negative Gram, Its composition varies very slightly according to the kind even of the species of the bacterium concerned. It is mainly made of several layers of polymer of N-acétylglucosamine (NAG) and of Acide N-acétylmuramique (NAM) in alternate series. The positive peptidoglycane of the gram is crossed laterally by large chains polymeric which connects it to the plasmic membrane: acids lipotéichoïques. Of another chains like the acids téichoïques are contained in the peptidoglycane and ensure its stability .

Space periplasmic, much narrower than at the negative Gram, is a storage space of Enzyme S, of Nutriment S, Protéine S, Ion S… It has many of other functions in particular in certain stages of the Synthèse of protein and in the Métabolisme. It is located between the layer of Peptidoglycane and the plasmic membrane.

The membrane has porous proteins leading in space periplasmic (Synthèse of protein). The plasmic membrane contains many other proteinic complexes of vital importance for the bacterium (as ATP synthase ) which have paramount roles in the bacterial metabolism.

Description of the stocks

The bacteria positive Gram are for the majority of the nondemanding germs, i.e. they easily cultivate in the basic mediums. The majority of the hulls are grams positive but many bacilli is also gram positive.

Examples of bacteria gram positive

Kind Staphylococcus ;
Kind Micrococcus ;
Kind Lactococcus ;
Kind Lactobacillus ;
Kind Clostridium ;
Kind Bacillus ;
Kind Streptococcus
Kind Enterococcus
Kind Listeria

Discrimination enters the bacteria in positive Gram is done by the research of the Catalase.

The research of the catalase

Realization

On a clean microscopic blade, to deposit a hydrogen peroxide drop (or Hydrogen peroxide H₂O₂). To take on a medium gélosé, the colony to be tested by means of a Pipette sterile Pasteur or of a metal ensemencor and to deposit the colony in the drop.

Observations and conclusions

If one observes a gaseous emission (Dioxygène), one says that the result is positive, the stock is catalase +. If one observes no gaseous emission, one says that the result is negative, the stock is catalase -.

See too

negative Gram.
the Yeast S: appear purple with the coloring of Gram but one cannot say in so far as they are positive Gram because they do not have at all the same characteristics of envelope.
the Mycobactérie S constitute an exception, because they are not colourable by the coloring of Gram: one indicates them like acido-alcoolo-resistant. See Coloring of Ziehl-Neelsen.

Random links: