抗生素英文课件精品MicrobiologyPrinciples and .ppt

Antimicrobial Agents A special group of chemotherapeutic agents used to treat diseases caused by microbes Antibiosis: literally means “against life” Antibiotic: A chemical substance produced by microbes which has the capacity to inhibit or destroy the growth of bacteria/other microbes Synthetic/semi-synthetic drugs 1910: Paul Ehrlich used Salvarsan to treat syphilis 1935: Gerhard Domagk discovered prontosil, a red dye, inhibits growth of many gram-positive bacteria 1936: Ernest Fourneau discovered that the sulfanilamide portion contained antimicrobial activity Selective Toxicity The Spectrum of Activity Modes of Action Side Effects The Resistance of Microorganisms The antimicrobial agent must harm the microbes without causing significant damage to the host Toxic dosage level: causes host damage Therapeutic dosage level: successfully eliminates the pathogenic organism if the level is maintained The range of different microbes against which an antimicrobial agent acts Broad spectrum: Agents effective against both gram-positive and gram-negative bacteria Narrow spectrum: Agents effective against a small number of microbes Inhibition of cell wall synthesis Disruption of cell-membrane function Inhibition of protein synthesis Inhibition of nucleic acid synthesis 5. Action as antimetabolites Inhibiting cell wall synthesis selectively damages bacterial and fungal cells Penicillin and cephalosporin contain a structure called a ?-lactam ring The ?-lactam ring attaches to the enzymes that cross-link peptidoglycans and prevent cell wall synthesis Certain polypeptide antibiotics, such as polymyxins Act as detergents and distort bacterial cell membranes Bind to phospholipids in the membrane Especially effective against gram-negative bacteria which have an outer membrane An example of selective toxicity Attack bacterial cells without significantly damaging animal cells Aminoglycoside antibiotics: Tetracycline, Erythromycin, streptomycin, chloramphen