[Kinds of antimicrobial agents and their mode of actions]

Hardness of development of drug-resistant bacteria has cross relation with mechanisms of antibacterial activities of antimicrobial agents. When the site of action of certain antibiotic is single enzyme and the enzyme can be converted to tolerant against the antibiotic by change of single amino acid retaining the enzymatic activity, drug-resistant bacteria can emerge easily. On the other hand, if the site of action is complex metabolic reactions, the drug-resistant bacteria would emerge hardly, because multiple mutations are required in this case. So that knowledges of mechanisms of antimicrobial agents are important to prevent the development of drug-resistant bacteria. Antimicrobial agents are classified into several categories, i.e. inhibitors for bacterial cell wall such as beta-lactam drugs, fosfomycin, and vancomycin; inhibitors for protein biosynthesis such as tetracyclibnes, macrolides, aminoglycoside antibiotics; inhibitors for DNA synthesis such as 4-quinolones; inhibitors for RNA synthesis such as rifampicin.