Intro to antibiotics.docx

Antibiotics- chemical compounds used to treat infections caused primarily by bacteria: they should be sufficiently non-toxic to be given to the infected host. Used to supplement body’s natural defences to bacterial infection by either killing or inhibiting them. Uses Treating and preventing bacteria...

Antibiotics- chemical compounds used to treat infections caused primarily by bacteria: they should be sufficiently non-toxic to be given to the infected host. Used to supplement body’s natural defences to bacterial infection by either killing or inhibiting them. Uses Treating and preventing bacterial infections Pre-post-surgery or trauma Agriculture- livestock Classification of antibiotics Natural antibiotics- produced naturally by fungi or bacteria to selectively inhibit the growth of others. Semi-synthetic antibiotics- chemically modified natural antibiotics e.g. ampicillin. Totally synthetic antibiotics- manufactured. Antibiotics can work in either of 2 ways. Bactericidal- kills the bacteria. Bacteriostatic- prevents bacteria from dividing. Antibiotics can be either: Broad spectrum- kills wide range of bacteria. Narrow spectrum- kills specific type or group of bacteria. How do antibiotics work? Different parts of the bacteria can be targeted such as the peptidoglycan cell wall or the metabolism etc. B-Lactam Antibiotics Targets peptidoglycan cell wall Has a ring structure. Can be penicillin, Amoxicillin etc. When penicillin was discovered, it was penicillin G which was able to be hydrolysed by acid (HCL in stomach) hence couldn’t be used in the clinics. The penicillin was manipulated, and the structure was changed= very stable in acidic environment. Penicillin kills bacteria by weakening their cell walls (BACTERICIDAL) made of peptidoglycan which is a chain-link structure. Structure of peptidoglycan Transpeptidase (penicillin binding protein) catalyse the final stages of peptidoglycan formation- links NAG & NAM together. B-Lactam Antibiotics inhibit the transpeptidase. The cross links are inhibited in the peptidoglycan which provide its structural integrity= cell bursts open. This is competitive inhibition= irreversible Transpeptidase recognises D alanine and D alanine= forms a cross bridge. Antibiotic resistance Ability of bacteria to survive treatment by certain antibiotics. *Lab tests fall into 2 main categories* 1. Diffusion- disk diffusion assay AD= simple and inexpensive DISAD= qualitative, no information on antibiotic concentration. 2. Dilution- minimum inhibitory. AD= greater accuracy, quantitative. DISAD= more expensive and labour intensive.