Antimicrobial agents and mode of action

Antimicrobial agents are chemical substance that kills or inhibit the growth of microorganism such as bacteria, fungus and yeast. Most of this agents are found in the nature and some are artificial synthesized. They are used for sterilization of instruments, cultures or even wounds. 

Alexander Fleming is the first person to discover a natural antimicrobial agent i.e penicillin. After that vast number of agents are discovered or synthesized in the lab. 

Chemical class	Examples	Biological source	Spectrum (effective against)	Mode of action
Beta-lactams (penicillins and cephalosporins)	Penicillin G, Cephalothin	Penicillium notatum and Cephalosporium species	Gram-positive bacteria	Inhibits steps in cell wall (peptidoglycan) synthesis and murein assembly
Semisynthetic beta-lactams	Ampicillin, Amoxicillin		Gram-positive and Gram-negative bacteria	Inhibits steps in cell wall (peptidoglycan) synthesis and murein assembly
Clavulanic Acid	Augmentin is clavulanic acid plus Amoxicillin	Streptomyces clavuligerus	Gram-positive and Gram-negative bacteria	Inhibitor of bacterial beta-lactamases
Monobactams	Aztreonam	Chromobacterium violaceum	Gram-positive and Gram-negative bacteria	Inhibits steps in cell wall (peptidoglycan) synthesis and murein assembly
Carboxypenems	Imipenem	Streptomyces cattleya	Gram-positive and Gram-negative bacteria	Inhibits steps in cell wall (peptidoglycan) synthesis and murein assembly
Aminoglycosides	Streptomycin	Streptomyces griseus	Gram-positive and Gram-negative bacteria	Inhibits translation (protein synthesis)
	Gentamicin	Micromonosporaspecies	Gram-positive and Gram-negative bacteria esp.Pseudomonas	Inhibits translation (protein synthesis)
Glycopeptides	Vancomycin	Amycolatopsis orientalisNocardia orientalis(formerly designated)	Gram-positive bacteria, esp.Staphylococcus aureus	Inhibits steps in murein (peptidoglycan) biosynthesis and assembly
Lincomycins	Clindamycin	Streptomyces lincolnensis	Gram-positive and Gram-negative bacteria esp. anaerobicBacteroides	Inhibits translation (protein synthesis)
Macrolides	Erythromycin Azithromycin	Streptomyces erythreus	Gram-positive bacteria, Gram-negative bacteria not enterics, Neisseria, Legionella, Mycoplasma	Inhibit translation (protein synthesis)
Polypeptides	Polymyxin	Bacillus polymyxa	Gram-negative bacteria	Damages cytoplasmic membranes
	Bacitracin	Bacillus subtilis	Gram-positive bacteria	Inhibits steps in murein (peptidoglycan) biosynthesis and assembly
Polyenes	Amphotericin	Streptomyces nodosus	Fungi (Histoplasma)	Inactivate membranes containing sterols
	Nystatin	Streptomyces noursei	Fungi (Candida)	Inactivate membranes containing sterols
Rifamycins	Rifampicin	Streptomyces mediterranei	Gram-positive and Gram-negative bacteria,Mycobacterium tuberculosis	Inhibits transcription (bacterial RNA polymerase)
Tetracyclines	Tetracycline	Streptomycesspecies	Gram-positive and Gram-negative bacteria, Rickettsias	Inhibit translation (protein synthesis)
Semisynthetic tetracycline	Doxycycline		Gram-positive and Gram-negative bacteria, RickettsiasEhrlichia,Borrelia	Inhibit translation (protein synthesis)
Chloramphenicol	Chloramphenicol	Streptomyces venezuelae	Gram-positive and Gram-negative bacteria	Inhibits translation (protein synthesis)
Quinolones	Nalidixic acid	synthetic	Mainly Gram-negative bacteria	Inhibits DNA replication
Fluoroquinolones	Ciprofloxacin	synthetic	Gram-negative and some  Gram-positive bacteria (Bacillus anthracis)	Inhibits DNA replication
Growth factor analogs	Sulfanilamide, Gantrisin, Trimethoprim	synthetic	Gram-positive and Gram-negative bacteria	Inhibits folic acid metabolism (anti-folate)
	Isoniazid (INH)	synthetic	Mycobacterium tuberculosis	Inhibits mycolic acid synthesis; analog of pyridoxine (Vit B6)
	para-aminosalicylic acid  (PAS)	synthetic	Mycobacterium tuberculosis	Anti-folate