Penicillin is the oldest known antibiotic in the whole world and what is really surprising that it was discovered by total coincidence. It was discovered by Alexander Fleming in the late nineteenth century when he was trying to multiply the penicillum fungi in the lab. Penicillin is still used till now for the treatment of many bacterial and fungal infections and of course it was developed immensely since that time.

There are now different categories of penicillin but the core of these categories is the natural penicillin or what is known the penicillin G. natural penicillin is effective against most of the gram positive microorganisms like streptococcus and staphylococcus. It is also effective against some gram negative bacteria and it is mainly used for treatment of oral cavity infections.

The second category of penicillin antibiotic is penicillinase resistant antibiotics. Oxacillin and cloxacillin are prominent examples for this group. This group does not target a wide range of microorganisms like the natural penicillin but it targets a specific group of bacteria which produces the beta lactamase enzyme. The lactamase producing bacteria are resistant to natural penicillin.

The third category of penicillin antibiotics is the aminopenicillins. Amoxicillin is the best example for this group and it is widely used today. This is group is very potent against gram negative bacteria like E-coli and Hemophelus influenza. The best feature of this group of penicillin antibiotics is that they can tolerate the gastric acid. This means that they could be administered orally without being degraded through the acid medium of the stomach.

The fourth group is called the extended penicillin antibiotics, although this group is effective against many gram - negative microorganisms but they are still inactive against beta- lacatam producing bacteria like the aminopinicillins.

The four categories of penicillin are still used till now to combat different types of microorganisms and every category is used to perform its specific role. All penicillin drugs act in the same way by affecting the bacterial cell wall. Suppression the formation of the bacterial cell wall will cause the bacteria to die and omit the effect of the microorganism on the body, the best feature of penicillin is that it develops the least side effects on the patient.