Tetracyclines

Tetracycline is an antibiotic group that works by preventing the growth and spread of bacteria, and they are named for their 4 hydrocarbon rings. Tetracyclines are used primarily for treating infections as well as controlling acne and rosacea (1). The 6 members of the tetracycline group are oxytetracycline, tetracycline, demeclocycline, methacycline, doxycycline, and minocycline (2). Once inside the bacterial cell wall, tetracyclines bind reversibly to the 30S ribosomal subunit to block the binding of the aminoacyl-tRNA to the acceptor site on the mRNA-ribosome complex (2). Blocking translation will cause a stoppage of protein synthesis in the bacteria cell. A unique side effect for tetracyclines is phototoxicity, or an increased risk of sunburn. Other side effects of taking this antibiotic include itching of the rectum or vagina, sore mouth, changes in skin color, severe headache, blurred vision, and dark-colored urine (1). Tetracyclines used to be helpful for a variety of bacterial problems, but resistance buildup by bacteria has changed that. Bacteria have used two main types of resistant mechanisms: tetracycline efflux and ribosomal protection. Efflux is responsible for moving toxic substances, such as antibiotics, out of the cell. An animation of how efflux is done can be seen in the video below. Ribosomal protection protein Tet(O) is a translational GTPase with high similarity to the elongation factor EF-G. This will "protect" the ribosome from binding with the tetracycline antibiotic during translation (3). Efflux resistance genes are generally found on plasmids, whereas genes involved in ribosome protection have been found on both plasmids and conjugative transposons (both are transmissible elements). Tetracyclines are excreted via urine and feces into the environment, creating estrogen effects and antibiotic resistant microorganisms (4).

References:
1. "Tetracycline: MedlinePlus Drug Information." U.S National Library of Medicine. U.S. National Library of Medicine, n.d. Web. 19 Oct. 2013.
2. May, Byron. "Tetracyclines." Tetracyclines. N.p., n.d. Web. 19 Oct. 2013.
3. Li, Wen. Mechanism of Tetracycline Resistance by Ribosomal Protection Protein Tet(O). N.p., July 2012. Web. 19 Oct. 2013.
4. Daghrir, R. "Tetracycline Antibiotics in the Environment: A Review." Environment Chemistry Letters. N.p., Sept. 2013. Web. 11 Nov. 2013.