What is Penicillin?

Alright, my trends challenge grinded to a hold, when I so sick that I needed penicillin. Now I'm starting to feel better, so I decided to write about penicillin. :-)

Penicillin was discovered in 1928 by accident by bacteriologist Alexander Fleming. When working with bacteria at St. Mary's Hospital in London, one of his petri dishes with staphylococcus bacteria was contaminated with fungus. He observed that the bacteria could not grow close to the fungal colony. He identified the fungus as Penicillium chrysogenum. He discovered the antibacterial activity was present in a filtrate of a broth when the fungus had grown, and called the filtrate penicillin.

Fleming cultivated the fungus and examined the broths effect on various bacteria. He found out the filtrate had antibacterial activity in many pathogenic Gram-positive bacteria, responsible for diseases like scarlet fever, meningitis, pneumonia and diphtheria. However, it had no effect on Gram-negative bacteria except Neisseria species responsible for gonorrhea and meningitis.

In 1939, ten years after Fleming's fortunate discovery, it was Howard Walter Florey and Ernst Boris Chain from Oxford University who managed to extract penicillin in powder form and show that they had a clinical response to infectious disease in animals. The volumes, which they had isolated was too small to be used for clinical trials in humans.

In 1941, the British researchers went to the U.S. where they got help from the Peoria Lab to develop a method for producing large quantities of penicillin. They used a different strain of Penicillium chrysogenum, as it grew better in the deep fermentation tanks and thereby producing more penicillin. In 1943 they performed the necessary clinical trials on humans and production was quickly scaled up. It was thus possible to treat wounded Allied soldiers on D-Day during second World War II. After intensive research, they succeeded in isolating and purifying penicillin.

In 1945 the structure of benzylpenicillin was solved by Dorothy Crowfoot Hodgkin using X-ray crystallography.

That same year Fleming, Florey and Chain received the Nobel Prize in medicine and physiology.

How does penicillin work?

Penicillins act by inhibiting the formation of peptidoglycan cross-linkages in the bacterial cell wall. This weakens the cell wall and causes the bacteria to lyse due to osmotic pressure. By mimicking the amino acid sequence D-alanyl-D-alanine, the β-lactam ring binds to the enzyme DD-transpeptidase (also called the penicillin-binding protein or PBP), which thus can not form cross-linkage.

Written by Jannich Brendle tor 08 december 2011 In Blogging