Antibiotics are now widely used to cure viral diseases. An antibiotic is a substance or compound that kills or inhibits the growth of bacteria (Davey PG, 2000). Ever since 1928, when Penicillin, the first natural antibiotic, was discovered by Alexander Fleming (Brown, Kevin, 2004), and 1940, when Penicillin was first using in clinic, the diversity of antibiotics has been discovered or made up to thousands of kinds. Penicillin refers to a group of antibiotics derived from Penicillium fungi (Dorland's Medical Dictionary, 2007). Its discovery is historically significant because it can damage the cell wall of bacteria and kill the bacteria cell at its reproduction stage, and it is the first medicine that can cure human diseases, such as syphilis and Staphylococcus infections (Wikipedia, 2010). Even in today's world, penicillins are still popularly used. For example, in China, the doctor will prescribe Amoxicillin for the patient as long as they catch a tonsil inflammation, which also leads to another discussion on misusing antibiotics. In this paper, I am going to discuss the information on penicillin, describe its process and talk a little about its huge impact to human beings.
Fungal description
It is well known that penicillin was discovered by accident in 1928 by Alexander Fleming. However, he is not the first one to use its properties. Dating back to ancient times, Greek and India already held the methods of using moulds and other plants to treat infection (Wikipedia, 2010). Fleming's breakthrough was on the Friday morning, September 28, 1928, in the basement of St. Mary's Hospital, London: his own laboratory. He mistakenly left open a Staphylococcus plate culture. Three weeks after his vacation, he noticed the plate was contaminated by blue-green mould and there was a halo of inhibited bacterial growth around the mould. He concluded that the mould must be able to release a substance that can inhibit the growth and lyse the bacteria (Fleming A., 1929).
The core skeleton of penicillin is R-C9H11N2O4S (R is a variable group) showed in Figure 1. Its molecular weight (MW) is around 313 to 334 g/mol.
Penicillin is derived from Penicillium fungi. Penicillium belongs to the genus of ascomycetous (Breuil et al., 2010). The macroscopic view of Penicillium is showed in Figure 2. One can see its greenish color and little fluffy shape at the outer ring of the colonies. The color of the central part is darker, and fades as it goes outside. The outer part is a sectorial shape. The microscopic view of Penicillium is showed in Figure 3. The mycelium consists of a highly branched network of multinucleate, septate, often colorless hyphae. Many branched conidiophores sprout from the hyphae. Then, on the top, it branches again with sterigmata, bearing conidiospores. Conidiospores are the asexual reproduction part and usually green (Wikipedia, 2010). When the spores are mature enough, they leave the sterigmata and spread all over. The green color one can see on the petri dish is from the spores. Conidiophores grow vertically on the plate. The colorless or white part is the hyphae.
Mechanism
All penicillins are β-lactam antibiotics (Holten KB et al., 2000). Β-lactam antibiotics are bactericidal, and work by inhibiting the synthesis of the peptidoglycan layer of bacterial cell walls (Britta et al., 1997). The function group of penicillin binds with DD-transpeptidase, which is a kind of enzyme. This enzyme can react with the peptidoglycan molecules in bacteria, leading to the breakdown of cell wall by cytolysis. Also, peptidoglycan precursors can induce the bacterial cell wall hydrolases (enzyme) and autolysins. This process can further digest peptidoglycan (Britta et al., 1997).
Because the inhibition of peptidoglycan, aminoglycosides are able to penetrate the bacterial cell wall. This shows that penicillins have a synergistic effect with aminoglycosides. As long as aminoglycosides go into the cell wall, it stops the bacterial protein synthesis (Britta et al., 1997).
Penicillins, like other β-lactam antibiotics, can block not only the division of bacteria, including cyanobacteria, but also the division of cyanelles, the photosynthetic organelles of the glaucophytes, and the division of chloroplasts of bryophytes. In contrast, they have no effect on the plastids of the highly developed vascular plants. This supports the endosymbiotic theory of the evolution of plastid division in land plants (Britta et al., 1997).
Impact
Penicillin is an effective, low toxic and widely used clinical antibiotic. It has been used in medical application since March 14, 1942, when John Bumstead and Orvan Hess first saved a dying patient's life using penicillin (Saxon W., 1999). After that, it has saved billions of millions of lives, especially during World War II. Penicillin made a major difference in the number of deaths and amputations caused by infected wounds among Allied forces, saving an estimated 12%-15% of lives (Wikipedia, 2010).
The discovery of penicillin improved the immunity of human beings and drove the development of antibiotics.
In this decade, though many types of bacteria are now resistant to penicillins, medicine like amoxicillin is still used to fight against bacterial-related diseases. Common used penicillins are listed in Table 1.
Conclusion
Penicillin has a history of 70 years. It was derived from Penicillium fungi and discovered by accident. It acts by inhibiting the synthesis of peptidoglycan layer of bacterial cell walls. The utilization of antibiotics is a huge step to human in fighting with diseases, and with the development of technology, not only penicillins, but also all the family of antibiotics will have a bright future.
Appendix
Figure 2 Penicillin G, Antibiotic; inhibits murein synthesis in bacterial cell wall (Manuela, 2008).
Figure 1 Penicillin core structure, in 3D. Purple is variable group (Benjah-bmm27, 2007).Penicillin-nucleus-3D-balls.bmp penicillin_g_link.jpg
Figure 3 Conidiospores of Penicillium (Gary E. Kaiser, 2005).penicillium1_final.jpg
Table 1 Common used penicillins and its application and side-effects (Robert, 1999).
Penicillin
Amoxicillin
Flucloxacillin
broad spectrum antibiotic, streptococcal infection, syphilis, Lyme disease
Ampicillin
Mezlocillin
Azlocillin
Nafcillinum
Carbenicillin
Penicillin
Cloxacillin
Piperacillin
Dicloxacillin
Ticarcillin
