1. Antibiotics By Dr. Humodi A. Saeed Associate Prof. of Medical Microbiology College of Medical Lab. Science Sudan University of Science and Technology E mail address: Biotechsust@hotmail.com

6. Definition of Antibiotic A substance of biological, semisynthetic or synthetic origin of low molecular weight ( non-protein) produced by a fungus or bacterium as secondary metabolites that inhibits or stop growth of other microorganisms in vitro and in vivo selectively, when it used in low concentration.

7. Characteristics of Antibiotics  It must be able to reach the part of the human body where the infection is occurring.

8. Characteristics of Antibiotics  It should not cause the development of resistant forms of parasites.

9. Characteristics of Antibiotics  It should not produce undesirable side effects in the host such as allergic reaction, nerve damage or irritation of the kidneys and gastrointestinal tract.

10. Characteristics of Antibiotics  It should be given orally without inactivation by stomach acid, or by injection (parenterally) without binding to the blood proteins.

11. Characteristics of Antibiotics  Finally, it should have a high level of solubility in the body fluids and be possible to achieve concentrations in the tissue or blood, which are sufficiently high to inhibit or kill the infectious agent.

12. Major groups of Antibiotics Beta-lactam antibiotic 1. Penicillin 2. Cephalosporins 3. Carbapenems 4. Monobactams

13. Toxicity Problem  The main toxicity problem with these antibiotics is an allergic reaction that occurs because of formation of beta- lactam/serum protein conjugate that elicits an inflammatory immune response.

14. Mode of Action  The beta-lactam antibiotics inhibit the last step in peptidoglycan synthesis, the transformation reaction that cross links the peptide side chains of the polysaccharide peptidoglycan backbone.

15. Spectrum  Some are effective against both Gram- positive and Gram- negative bacteria whereas others are more effective against Gram- positive than Gram- negative bacteria or vice versa.