What is Penicillin

One of a series ofbeta-lactam antibiotics, all of which possess a four-ring beta-lactam structure fused with afive-membered thiazolidine ring. These antibiotics are nontoxic and kill sensitive bacteria during their growth stage by the inhibition of biosynthesis of their cell wall mucopeptide.

The antibiotic properties of penicillin were first recognized by A. Fleming in 1928 from the serendipitous observation of a mold, Penicillium notatum, growing on a petri dish agar plate of a staphylococ-cal culture. The mold produced a diffuse zone which lysed the bacterial cells. Commercial production of penicillin came from the pioneer work of E. Chain and H. W. Florey in 1938, first in England and then in the United States, where it was developed from an academic project into a collaborative war effort between industry and government research. Penicillin (as penicillin G) was made available to the allied troops in Europe in the latter part of the World

War II.

Penicillin is produced from the fungal culture P. chrysogenum that was isolated from a moldy cantaloupe. The pharmaceutical industry uses highly mutated strains cultured in large, highly aerated, stirred tank fermentors controlled to optimize antibiotic production and to efficiently use raw materials such as corn syrup, corn steep liquor, and cottonseed flour. Temperature, pH, dissolved oxygen, soluble nitrogen and ammonia levels, and sugar feed rates are important control factors. The biosynthesis of penicillin is known in detail, and all the enzymes involved in the formation of this secondary metabolite have been isolated and purified.
Penicillin G, the most commonly fermented penicillin, is produced by the addition of a precursor phenylacetic acid to the growing culture. Use of phe-noxyacetic acid as a precursor produces penicillin V Both penicillins are recovered by extraction into organic solvents at acid pH and precipitation as their potassium or sodium salt.

Penicillin G is generally given by injection against penicillin-sensitive streptococci such as pneumo-cocci (meningitis), and in treatment of endocarditis and gonorrhea. Penicillin G procaine salt is used for intramuscular injection to provide quick distribution of the antibiotic. Penicillin G benzathine salt is used for slower release. Penicillin G can be given in combination with probenecid, a compound which delays urinary excretion. Penicillin V is acid stable and is usually given orally. It is effective in the treatment of upper respiratory infections and periodontal work.
More effective semisynthetic penicillins are produced by coupling different side chains to the active penicillin nucleus 6-aminopenicillanic acid. This nucleus is produced from either penicillin G or penicillin V by using specific immobilized enzymes. The various side chains confer different antibiotic properties on the penicillin.

The fermented penicillin G and penicillin V are susceptible to destruction by an enzyme (beta-lactamase) produced by certain bacteria which makes them resistant. The penicillins methicillin, oxacillin, nafcillin, cloxacillin and dicloxacillin all are resistant to hydrolysis by beta-lactamases and are used to treat staphylococcal infections. Cloxacillin and dicloxacillin are used orally. Ampicillin and amoxicillin are penicillins with extended spectra as they are effective against many gram-negative bacteria. They are used mainly orally against streptococci and other respiratory-tract pathogens, including Haemophilus influenzae,in the treatment of sinusitis, bronchitis, and pneumonia. They are used extensively in pediatrics and against Listeria mono-cytogenes and Salmonella spp.

Hetacillin, pivampicillin, and bacampicillin are effective pro drug forms of ampicillin. Amoxicillin is formulated with a beta-lactamase inhibitor clavu-lanic acid as Augmentin for the treatment of ampicillin-resistant infections. Carbenicillin, ticar-cillin, azlocillin, mezlocillin, and piperacillin were developed to combat pseudomonad, enterobacter, and serratia infections resistant to ampicillin. They are used mainly to treat urinary Pseudomonas aeruginosa infections, sepsis from burns, and chronic infections of the respiratorytract.
Reference : McGraw - Hill Encyclopedia of Science and Technology