Penicillin is a group of antibiotics derived from Penicillium fungi. They include penicillin G, procaine penicillin, benzathine penicillin, and penicillin V. Penicillin antibiotics are historically significant because they are the first drugs that were effective against many previously serious diseases, such as syphilis, and infections caused by staphylococci and streptococci. Penicillins are still widely used today, though many types of bacteria are now resistant. All penicillins are β-lactam antibiotics and are used in the treatment of bacterial infections caused by susceptible, usually Gram-positive, organisms.

Medical uses

The term "penicillin" is often used generically to refer to benzylpenicillin (penicillin G), procaine benzylpenicillin (procaine penicillin), benzathine benzylpenicillin (benzathine penicillin), and phenoxymethylpenicillin (penicillin V).

Procaine penicillin and benzathine penicillin have the same antibacterial activity as benzylpenicillin but act for a longer period. Phenoxymethylpenicillin is less active against Gram-negative bacteria than benzylpenicillin. Benzylpenicillin, procaine penicillin and benzathine penicillin are given by injection (parenterally), but phenoxymethylpenicillin is given orally.

Discovery

The discovery of penicillin is attributed to Scottish scientist and Nobel laureate Alexander Fleming in 1928. He showed that, if Penicillium notatum were grown in the appropriate substrate, it would exude a substance with antibiotic properties, which he dubbed penicillin. This serendipitous observation began the modern era of antibiotic discovery. The development of penicillin for use as a medicine is attributed to the Australian Nobel laureate Howard Walter Florey, together with the German Nobel laureate Ernst Chain and the English biochemist Norman Heatley.

Medical use
Penicillin kills bacteria by interfering with the ability to synthesize cell wall. In this sequence, Escherichia coli were incubated in penicillin for 30 minutes. The bacteria lengthen, but cannot divide. Eventually the weak cell wall ruptures .

Inappropriate use of antibiotics (prophylactic treatment of herds in meat production and pointlessly treating viral infections with antibacterials) flood our environment with drugs that select for populations of antibiotic-resistant bacteria. Although penicillin was a wonder drug when discovered, some bacteria exposed to penicillin survived because they produced the enzyme β-lactamase that destroys penicillin’s structure. A solution was to devise other penicillin-like antibiotics (β-lactams) with structures that are not destroyed by β-lactamase.

Methicillin is one of those drugs developed in the late 1950’s. Unfortunately, an increasing threat is now Methicillin-Resistant Staph aureus (MRSA) which avoids methicillin and other β-lactams by an alteration in MRSA's penicillin target-binding site. Bacteria are constantly evolving such new defenses, so treatment of bacterial infections requires a constant search for antibiotics with novel modes of action.

superbug, methicillin resistant Staph aureus, Streptococcus pneumoniae, antibiotic misuse, vancomycin resistant Enterococcus, cephalosporin, penicillinase, antibiotic resistance