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Antibiotics are chemotherapeutic agents used to inhibit or kill bacteria. There are many different classes of antibiotic drugs, each exerting a different type of inhibitory effect that specifically impacts bacteria.

Bacterial cells are prokaryotic; primitive cells that differ significantly from humans' eukaryotic cells. Antibiotics are selectively toxic, meaning that they can destroy microbes without harming the eukaryotic cells of the host. Penicillins, and other beta-lactam antibiotics, work by inhibiting the synthesis of the bacteria cell wall.

Each article in this Antibiotic Mode of Action Series covers a specific class of antibiotic and includes the following information:

* a list of the specific antibiotics that fall in the class (generic and brand names)
* mode of action
* type of infection the antibiotic class to against
* type of bacteria inhibited or killed
* pros and cons of using the class of antibiotics

The main classes of antibiotics include:

* Aminoglycosides
* Cephalosporins (a Beta-lactam)
* Macrolides
* Penicillin (a Beta-lactam)
* Quinolones (Fluoroquinolones)
* Sulfonamides
* Tetracyclines

* History of Penicillin *

In 1929 Alexander Fleming, a British bacteriologist, inadvertently discovered penicillin. He had observed bacterial Staphylococci colonies disappearing in cultures that were contaminated with mold. Fleming eventually extracted the compound from the mold that had been responsible for destruction of the bacterial colonies. The product was named penicillin, after the Penicillium mold from which it was derived.

Penicillins include the following drugs (this is not a complete list):

* amoxicillin
* ampicillin
* bacampicillin
* oxacillin
* penicillin

* Penicillin Mode of Action *

Penicillins and cephalosporins (beta-lactam antibiotics) work by interfering with interpeptide linking of peptidoglycan, the strong, structural molecule found specifically in bacterial cell walls. Cell walls without intact peptidoglycan cross-links are structurally weak, prone to collapse, and disintegrate when the bacteria attempts to divide. Since the eukaryotic cells of humans do not have cell walls or peptidoglycan, our cells are not damaged by penicillins.

* Antimicrobial Spectrum of Penicillins *

Penicillins have a bacteriocidal effect on Gram-positive bacteria. In Gram-positive cells, multiple layers of peptidoglycan make up as much as 90% of the thick, compact cell wall, including the outermost layer. Penicillins are not effective against Gram-negative bacteria, which have cell walls in which peptidoglycan is not the outermost layer, but instead exists in a single layer, protected between the plasma membrane and a lipopolysaccharide (LPS) outer membrane. Therefore, penicillin cannot access the peptidoglycan of Gram-negative cells.

* Type of Infections Penicillins Are Used For: Beta-lactam antibiotics are used to treat Gram+ bacterial infections which, depending on the specific microbe involved, cause a wide range of illnesses including skin infections, dental infections, ear infections,

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