The first known antibiotic, penicillin, was discovered by accident in 1928 by Alexander Fleming. Fleming noticed that a mold, from which the antibiotic was derived, killed all the bacteria around the mold. Further study led to the isolation of the compound penicillin and the ability to effectively kill bacteria was achieved. Antibiotics work by interrupting different growth factors required for bacterial growth, while leaving human cell biosynthesis unimpeded.
Bacterial Cell Wall
The bacterial cell wall is an ideal target for many antibiotics. Bacteria have a cell wall in the form of peptidoglycan. All bacteria have a cell wall, though some contain a thicker wall than others. The cell wall in bacteria is responsible for maintaining cell rigidity and for resisting cell membrane lysis from osmotic imbalance. According to the textbook "Microbiology: Sixth Edition", antibiotics like bacitracin, vancomycin and penicillin block steps in the synthesis of new cell wall subunits from being attached.
Protein Synthesis
Many antibiotics target bacterial specific protein synthesis. If the invading bacteria can't produce the proteins needed for survival, the cell will die. Protein gets synthesized off of ribosomes within the cell. Bacterial ribosomes are different from human ribosomes, and make an effective target for inhibition. Aminoglycosides, chloramphenicol, erythromycin and tetracycline target the bacterial ribosomes to stop protein production.
DNA synthesis
Bacteria possess specific enzymes, such as deoxyribonucleic acid gyrase, which interact with DNA during synthesis. Novobiocin, ciprofloxacin and nalidixic acid are the major antibiotics responsible for blocking enzymes associated with DNA synthesis. The antibiotics function very differently. Novobiocin effectively "outcompetes" the DNA gyrase enzyme for the binding spot. Ciprofloxacin and nalidixic acid bind to the actual DNA gyrase enzyme, ruining the enzymatic function.
Folic Acid Synthesis
Bacteria are unable to obtain folic acid from the environment due to the size of the molecule. It is unable to pass through the cell membrane. For this reason, bacteria must synthesize its own folic acid within the cell. Antibiotics which target folic acid synthesis include: sulfonamides, sulfones, trimethoprim, methotrexate and pyrimethamine. These antibiotics have different modes of action for inhibiting the synthesis of folic acid. As with many of the antibiotics above, some strains of bacteria have gained resistance to folic acid inhibitors.
References
- Nobelprize.org: The Nobel Prize in Physiology or Medicine 1945
- "Microbiology: Sixth Edition"; Lansing Prescott, John Harley and Donald Klein; 2005
- University of South Carolina School of Medicine: Antibiotics
