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.
Antibiotics have been used increasingly over the last 50 years in animal feed for a couple of reasons. The antibiotics act as an anti-microbial agent as well as a growth-promoting agent. There are now a dozen antibiotics put into animal feed, including chlorotetracycline, procaine penicillin, oxytetracycline, tylosin, bacitracin, neomycin sulfate, streptomycin, erythromycin, linomycin, oleandromycin, virginamycin, and bambermycins (1). These twelve antibiotics are of microbial origin, and on top of these there are other chemically synthesized antimicrobial agents. The three main groups of chemically synthesized antibiotics are arsenical, nito-furan, and sulfa compounds.
Antibiotics are used in animal feed at a rate of 2-50 grams per ton for improved performance of animals. The rate increases to 50-200 grams per ton when specific diseases are being targeted. From 2009-2011, 72 percent of all United States sales of antimicrobials comprised of those routinely added to water or animal feed (2). There are major benefits from antibiotics, including increased efficiency and growth rate, treating clinically sick animals, and greatly reducing the incidence of infectious disease. There are a lot of risks with using this amount of antibiotics in feed, however. After being fed this food filled with antibiotics, the animals start to retain the strains of bacteria that are resistant to antibiotics (2). The resistant bacteria are then transmitted to other animals, and the resistant bacteria do well in the intestinal flora of the animals. The three main ways bacteria can exchange genetic material with other bacteria are transformation, conjugation, and transduction. All three of these ways of exchanging genetic material can change genomes and create new, more powerful strands of resistant bacteria. Humans can become infected with the bacteria too, mostly from interaction and contact with the infected animals' feces or by eating the infected meat.
1. "Effects of Antibiotics on Animal Feed." N.p., 1998. Web. 10 Oct. 2013. 2. Wallinga, D. "Do Antibiotics in Animal Feed Pose a Serious Risk to Human Health?"ScienceDaily. ScienceDaily, 11 July 2013. Web. 19 Oct. 2013.
Cephalosporins are a group of beta-lactam antibiotics derived from the mold Cephalosporium. Beta-lactam antibiotics all contain a four membered beta-lactam ring with three carbons and a nitrogen, as well as a carbonyl group off one of the carbons. There are three groups: Cephalosporin N,C, and P. These three groups all have a slightly similar chemical makeup. Cephalosporin N and C are chemically related to Penicillins, and Cephalosporin P is a steroid related to fusidic acid. They act in the same manner as Penicillins in the fact that they disrupt bacterial cell wall synthesis. First generation Cephalosporins are active against Gram positive bacteria, whereas later generations are more successful against Gram negative bacteria (1). Some examples of these antibiotics are Cefamandole, Cefurxiome, Cefonicid, and Cefoxitin. Cephalosporins are used to treat step throat, peritonitis, diverticulitis, staph infections, bronchitis, sinusitis, pneumonia and gonorrhea (2). Cephalosporins, like all antibiotics, do not work on treating viruses. There are symptoms that come with taking Cephalosporins, including stomach cramps, nausea, vomiting, and facial flushing. These antibiotics can be taken orally intravenously, or intramuscular injection. Bacterial resistance mechanisms are possible, and there are three main mechanisms used by bacteria on cephalosporins. The first is the destruction of the beta-lactam ring by beta-lactamases. Next is altering the affinity of cephalosporins for their target site. Lastly, bacteria can cause decreased penetration of the antibiotic to the target site. This is only possible for gram-negative bacteria because gram-positive bacteria lack an outer cell membrane (3). Cephalosporins should not be combined with alcohol or taken with medicines that contain alcohol.
References: 1. "Livertox." Cephalosporins. N.p., 2011. Web. 19 Oct. 2013. 2. "CEPHALOSPORINS - INJECTION Side Effects, Medical Uses, and Drug Interactions." MedicineNet. N.p., 2013. Web. 19 Oct. 2013. 3. Itokazu, Gail. "CEPHALOSPORINS." CEPHALOSPORINS. N.p., n.d. Web. 19 Oct. 2013.
