History and Mechanisms of Antibiotics

Antibiotics

A chemical substance made by microorganisms to kill or inhibit BACTERIA

Antimicrobial agents

Chemotherapeutic agent used to treat diseases caused by a microbe

Disk diffusion or Kirby-Bauer

A method for determining sensitivities and resistance

Zones of inhibition

Size of zone related to degree of inhibition PLUS diffusion rate

Minimum inhibitory concentration (MIC)

The lowest concentration of an antimicrobial that will inhibit the visible growth of a microorganism

Broad spectrum

Useful if organism unknown

Narrow spectrum

Better choice if organism is known; minimizes harm to normal flora

Anti-metabolites

Inhibit metabolic processes in bacteria

Cell wall synthesis inhibitors

Antibiotics that prevent the formation of the bacterial cell wall

Penicillin

Discovered by Alexander Fleming in 1928; used to treat bacterial infections

Natural penicillins

Includes Penicillin G and Penicillin V, with specific administration routes

Semi-synthetic penicillins

Modified penicillins like Methicillin, Oxacillin, and Amoxicillin with broader spectrum

Cephalosporins

Antibiotics derived from fungus, often used when allergies to other drugs exist

Carbapenems

Antibiotics from bacteria that target peptidoglycan synthesis, reserved for resistant gram-negative rods

B lactamases

Enzymes produced by bacteria that cleave the b lactam ring

Polymyxins

Disruptors of cell membranes, often combined with bacitracin for topical treatment of gram (-)

Aminoglycosides

A class of antibiotics that affect bacterial ribosomes (30S)

Tetracyclines

Broad spectrum antibiotics that bind to ribosomes (30S) and are bacteriostatic

Chloramphenicol

Bacteriostatic antibiotic that affects the 50S subunits of ribosomes

Macrolides

Antibiotics like Erythromycin and Azithromycin that affect the 50S subunit

Rifampin

Inhibits RNA polymerase and prevents RNA synthesis, broad spectrum but primarily for TB

Quinolones

Synthetic antibiotics that block DNA gyrase

Resistance mechanisms

Include alteration of targets, membrane permeability, development of enzymes, and metabolic pathways

Resistance (R.) plasmids

Carry antibiotic resistance genes and can be transferred by conjugation

Synergism

Using 2 drugs at the same time that enhance each other's activities