What is Penicillin?
[[File:Penicillin core.svg|thumb|right|250px|Core structure of Penicillin: R is the variable group]] [[File:Penicillium notatum.jpg|thumb|Certain [[mold]]s naturally produce Penicillin]] '''Penicillin''' is a group of common [[antibiotics]], used to treat [[bacteria]]l infections. It was one of the first antibiotics to be discovered, and worked well against [[staphylococcus|staphylococci]] and [[streptococcus|streptococci]]. Many strains of bacteria are now [[antibiotic resistance|resistant]]. Chemists keep changing part of its structure in the effort to keep it working against the bacteria. Penicillin is sometimes used to treat [[syphilis]], [[tonsillitis]], [[meningitis]], and [[pneumonia]] as well as other diseases. == Mechanism == Penicillin can be used to enter and kill two types of bacteria, [[Gram-positive]] and [[Gram-negative]] bacteria. Gram-positive bacteria have no outer [[cell membrane]] (protective layer around the bacteria cell) and have large pores (holes) which allows penicillin to enter easily and kill the cell from the inside.<ref>{{Cite journal|last=Lambert|first=P.A.|date=2002-05-01|title=Cellular impermeability and uptake of biocides and antibiotics in Gram-positive bacteria and mycobacteria|url=http://dx.doi.org/10.1046/j.1365-2672.92.5s1.7.x|journal=Journal of Applied Microbiology|volume=92|pages=46S–54S|doi=10.1046/j.1365-2672.92.5s1.7.x|pmid=12000612 |s2cid=24067247 |issn=1364-5072}}</ref> Gram-negative bacteria are harder for penicillin to enter as they have smaller pores and an outer cell membrane so penicillin has to enter through smaller [[Aqueous solution|aqueous]] pores (holes in the membrane where water enters and leaves the cell). This means that killing Gram-negative bacteria takes a longer amount of time and some penicillin drugs may not work against them.<ref>{{Citation|last1=Masi|first1=Muriel|title=Outer Membrane Porins|date=2019|url=http://dx.doi.org/10.1007/978-3-030-18768-2_4|work=Subcellular Biochemistry|pages=79–123|place=Cham|publisher=Springer International Publishi