Penicillin

The penicillins are antibiotic beta-lactam antibiotics. At the base, penicillin is a toxin which comes from the mould Penicillium and which is inoffensive for the man. They are used in the treatment of bacterial infections, mainly against gram-positive germs. They were officially discovered, and in any case promoted, by the Scot Sir Alexander Fleming the September 3rd 1928 (Pénicilline G). They were introduced for therapies only starting from 1941 or 1943, thirteen years later. The German Chimie had preferred for its part to be directed in the way of the Sulfamidé S.

Chemical formula

Penicillins have as a chemical formula:

where R is a variable chain.

History

See also: Discovered penicillin

It is only when one learned how to oppose bacteria to bacteria that the large opening in the fight against the infectious illness was carried out. Penicillin was discovered on September 30th, 1928 by Alexander Fleming completely by chance. This Scottish researcher worked during several years to try to purify this Antibiotique. It is only into 1940 that two other researchers Florey and Chain, carried out the dream of Fleming by purifying penicillin. It however was exploited into therapeutic only towards 1940 and was up to that point used only to clean the boxes of $petri of their Bactérie S.

In 1996, penicillins were still an effective cure against the Pneumocoque; in 2001, the scientific community noted that this one presented a important resistance towards these antibiotics. It is the traditional effect darwinien: if 1% of a stock resist the blocking of its reproduction by an antibiotic, it is it only which will reproduce, and in the long term this stock will pass from 1% to 99% of the population. However, one is not yet there, and at present 85% of the pneumococci are still sensitive to penicillin. Moreover, there exists a form of Allergie to the penicillin which makes it inapplicable for certain people.

Mode of action

See also: Antibiotic beta-lactam antibiotic

Penicillins and the others antibiotic β-lactams act by inhibition of the formation of the bonds inter Peptidoglycane S in the cellular Paroi bacterial. Half Beta-lactam of penicillins binds to the Enzyme which should bind to the Molécule S of peptidoglycane of the Bactérie S and thus prevents the multiplication of the bacteria.

Penicillins do not kill the disease-causing agents on which they act: they block simply their mechanism of reproduction, which enables them not to submerge by their number natural defenses of the organization.

Alternatives

Penicillin benzathine

For Canada, penicillin benzathine is used exclusively against the Treponema pallidum , the bacterium of the Syphilis. This penicillin shape with slow release is given in only one intramuscular injection; the amount diffuses then slowly in the organization for one long period, at the end of which a primary education syphilis will be normally cured.

The benzylpénicilline (penicillin G)

Penicillin G is the intravenous shape of penicillin. One uses it for more severe infections where one cannot rely on penicillin in oral form. It has exactly the same spectrum of action as penicillin V, its perfect equivalent in oral form.

The phénoxyméthylpenicilline (penicillin V)

Penicillin V is the oral shape of penicillin. Its only difference compared to penicillin G is the route of administration.

The ampicilline (penicillin A)

Penicillin has is a penicillin with widened spectrum. The Ampicilline and especially the Amoxicilline are its two representatives.

Penicillins resistant to the penicillinases

Several bacteria resistant to conventional penicillins hold this resistance thanks to a family of enzymes, the penicillinases, which protect them by destroying the molecules from penicillin. It is the case in particular Staphylocoque gilded. To surmount this obstacle, of special penicillins were developed, which resist these defensive enzymes.

These penicillins are the méthicilline , the oxacilline and the cloxacilline ; they have all the same spectrum of action, that is to say that of conventional penicillins plus the bacteria protected by penicillinases, like the majority of the stocks of Staphylococcus aureus. They however do not have any action against or Staphylocoque aureus resistant to the méthicilline (SARM). The méthicilline, prototype of the family, are useful hardly than to carry out tests of sensitivity. The oxacilline is used clinically in the United States. In Canada, one employs the cloxacilline, which exists in intravenous and oral form.

The intravenous cloxacilline has unfortunately the defect to be very irritating for the veins, often involving venous thromboses (phlebitis) with the site of injection; moreover, its short half-life obliges to manage it each 4 hours. One thus prefers often a to him Céphalosporine, easier of employment.

Resistance

Primarily caused by the production of beta-lactamases of which penicillinases. At Gram negative, these beta-lactamases are periplasmic (between the two membranes). At positive Gram, they are at the level of the external plasmic membrane.

Developments at the beginning of penicillins

The narrow spectrum of penicillins, and the weak activity of the phénoxyméthylpénicilline activates per bone, led in the search of derived from penicillins able to treat a larger range of infections.

The first interesting progress was the Ampicilline. Later, one came to the Amoxicilline, prolonged effect.

Later the Flucloxacilline came Staphylococcus species. It is still No match for MRSA (Resistant Methicillin Staphylococcus aureus ). -->

Biosynthesis

See too

  • Roquefort (cheese) which was used, at one time, for its antibactériens effects contained in its blue mushroom, Penicillium.

References

Internal bonds

  • Antibiotic beta-lactam

External bonds

  • the discovery of Ernest Duchesne: http://perso.wanadoo.fr/santards.trad/grandes_figures.htm#duchesne
  • the thesis of Duchesne: http://lyon-sud.univ-lyon1.fr/bacterio/DOCDIV/Duchesne0.html
  • “official” history of penicillin: http://www.herodote.net/histoire09031.htm
  • the discovery of penicillin on the site CultureSciences-Chemistry of the National university
  • Determination of the structure and synthesis of penicillin on the site CultureSciences-Chemistry of the National university

Simple: Penicillin

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