Sir Alexander Fleming, a Scottish physician and microbiologist, returned from his holiday on 3 September 1928 to continue his project at St. Mary's Hospital in London. He noticed a bluish-green mold growing on his petri dish. He extracted it and investigated it further.

  It turned out that the mold was inhibiting the growth of Staphylococcus bacteria. He examined this mold further to realize it can easily kill off any bacteria. Back in the 1920s, bacterial infections were a common cause of deaths in the world. Therefore, he accidentally discovered a solution to that problem. 

  Soon, he kept producing the bacteria-killing mold and figured out ways to improve by mixing it with other chemicals such as corn steep liquor. This mold was called a Penicillium, it produces a juice to inhibit the formation of a bacterium's cell wall. The mold juice disrupts the synthesis of peptidoglycan, a key component of a bacterium's cell wall. Without a proper cell wall, the bacterium becomes vulnerable to internal pressure, causing it to burst and die.

  However, bacteria gradually adapted to becoming stronger against Penicillin. Thus, it became easier for bacteria to fight the Penicillium and other components of Penicillin. Nonetheless, with the help of organic and medicinal chemistry, new solutions for Antibiotics were generated and produced. The antibiotic's structure and adaptations were analysed, allowing scientists to modify it by fermenting it to make it pure, increasing its effectiveness. With modern-day technologies in addition up our sleeves, we can easily make new Antibiotics.