Common Antibiotics

Beta Lactum Antibiotics: Beta Lactum Antibiotics are chemicals that contain the 4-membered Beta Lactum Ring. They are produced by the fungus molds such as Pencillium and Cephalosporium. There antibiotics inhibit the last step in the bacterium's cell wall synthesis. Beta lactum antibiotics are useful against Gram-positive bacteria. Around 300-500 people die each year from an allergy to a beta lactum antibiotic. There are several kinds of beta lactum antibiotic:

•  Natural Penicillins are produced by fermentation of the fungus Penicillium notatum chrysogenum. They include Pencillin G and Penicillin V. They will kill streptococcus, gonococcus and staphylococcus. They are usually not effective against Gram-negative rod-shaped bacteria.

• Cephalolsporins are similar to penicillins and are made from a species of Cephalosporium. They are used as penicillin substitutes, and in surgical prophylaxis.

Semisynthetic penicillins: Semisynthetic penicillins were first used in 1959. A mold produces the main part of the molecule, which is then altered chemically. These antibiotics are usually constructed to have certain advantages over natural penicillins. Sometimes, chavulanic acid is added to a synthetic penicillin to extend the life of the drug. Here are some types of semisynthetic penicillin:

• Amoxycillin and Ampicillin are useful not only on Gram-positive bacteria, but also on some Gram-negative bacteria.
• Clavulanate also called Augmentin, is prepared by adding chavulanic acid to amoxycillin. Clavulanic acid is made from Streptomyces clavuligerus.

Bacitracin Antibiotic: Bacitracin Antibiotic is an antibiotic produced by a Bacillus species. It prevents the growth of the cell wall. Because of its high toxicity, it is not systemically used. It is used in topic antibiotics, and to sterilize the bowel before surgery, since it is not absorbed by the digestive tract.

Chloramphenicol: Chloramphenicol is produced by Streptomyces venezuelae. It works by inhibiting translation during protein synthesis. It is effective against both Gram-positive and Gram-negative bacteria. It is currently produced by chemical synthesis. Chloramphenicol causes aplastic anemia in a small percentage of patients, and ever since that was discovered, chloramphenicol has been used very little in non life-threatening situitions.

Polymyxin Antibiotic: Polymyxin is an antibiotic produced by Bacillus polymyxis. It works by inhibiting cell membrane growth. It is rather toxic to humans, so is therefore usually used only as a topical antibiotic. Occasionally, it is used to treat urinary tract infections, however it must be used under close hospital supervision, for it will easily damage the kidney and other organs.

Tetracyclines Antibiotics: Tetracyclines are a family of eight antibiotics, all products of Sptromyces. Some of these can now be produced synthetically. Tetracyclines block protein synthesis on isolated ribosomes. It concentrates in certain types of ribosomes possesed only by bacteria, so it is not toxic to the animal. Because of their extremely low toxicity, they were overused in the medical community, and now there is widespread resistance to tetracyclines. However, they are still useful in treatment of some diseases, such as Lyme disease.

Macrolides Antibiotics: Macrolides are produced by Streptomyces erythreus. Their chemical structures contain large lactone rings linked through glycoside bonds with amino sugars. Macrolides are inhibitors of protein synthesis. They are effective against Gram-positive bacteria and most Gram-negative bacteria, Neissera, Legionella, and Haemophilus, but not Enterobacteriaceae.

Aminoglycosides Antibiotics: Aminoglycosides are products of Spectromyces griseus. They are protein synthesis inhibitors binding to bacterial ribosomes to prevent the initiation of protein synthesis. They can be used against a wide variety of both Gram-positive and Gram-negative bacteria. Aminoglycoside usage has been limited because prolonged use has been found to cause kidney damage and injury to the auditory nerves, leading to deafness. Streptomycin has its primary use for treating tuberculosis patients.

• Gentamicin is used against many strains of Grma-positive and Gram-negative bacteria, including Pseudomonas aeruginosa
• Kanamycin is a complex of three different antibiotics. It is effective against many gram-positive bacteria, including penicillin-resistant staphlococci, even at low concentrations.
• Tobramycin, along with gentamicin, are the principal antibiotics used for treatments against Pseudomonas infections.

Nalidixic Acid: Nalidixic Acid is a synthetic chemotheraputic agent effective against Gram-negative bacteria. It binds to DNA gyrase enzyme (topoisomerase) and inhibits DNA duplication. It is a member of a group of compounds called the quinolones. It is mainly used in the treatment of urinary tract infections, and will kill several types of Gram-negative bacteria such as E. coli, Enterobacteriaceae aerogenes, K. pneumoniae, and Proteus species, which are common causes of urinary tract infections. It is not effective against Pseudomonas aeruginosa, and Gram-positive bacteria are usually resistant.

Rifamycines: Rifamycines are produced by Streptomyces mediterranei. They inhibit transcription in eubacterial RNA polymerase. A synthetic derivative of rifamycin is:

• Rifampicin is active against Gram-positive and Gram-negative bacteria. It is often used against Mycobacterium tuberculosis. It has a greater effect on the bacteria that causes tuberculosis than most other antibiotics. It has replaced isoniazid as the front-line drug to treat tuberculosis, especially where isoniazid resistance is present. It is also used to meningitis, caused by Neisseria meningitidis. It can be taken orally.

Sulfonamides: Sulfonmides were introduced in 1935 by Domagk. He discovered that these chemicals could cure mice with beta-hemolytic Streptococci infections. Sulfonamides are derived from the compound sulfanilamide. They are effective against Streptococcus pneumoniae, beta-hemolytic streptococci, and E. coli. The sulfonamides are used in treatment for urinary tract infections caused by E. coli and in treatment of meningococcal meningitis.

Isoniazid (INH): Isoniazid INH is primarily used in the treatment of tuberculosis. It works by inhibiting synthesis of mycolic acid. It is usually given together with rifampicin. It prevents the growth of bacteria resistant to rifampicin.

Paraaminosalicylic acid (PAS): Paraaminosalicylic acid is a chemotheraputic agent once used as the primary agent in tuberculosis treatment. Paraaminosalicylic acid is an anti-folate. It is used only as a secondary anti-tuberculosis agent, having been replaced by ethambutol.

Ethambutol: Ethambutol is a chemotheraputic agent used in the treatment of tuberculosis, works by inhibiting the incorporation of mycolic acids into the microbacterial cell wall.