Antimicrobial drugs: Their classification and resistance development
Microbial infections are the most life-threatening infections which require antimicrobial agents for their eradication. In the current practices of anti-infective therapy, those agents having a broad spectrum of activity and diverse therapeutic prospects are the most popular anti-microbial agents. The present article was focused on the various classes of antibiotics, their mechanism of action and the mechanisms by which the resistance was developed against those antibiotics.
Definition of antimicrobial drugs
Antimicrobial drugs are those which that kills or inhibits the growth of microorganisms such as bacteria, fungi etc. Antimicrobial drugs can kill microbes (known as microbicidal) and some can only prevent the growth of microbes (known as microbiostatic). Examples of some antimicrobial drugs: penicillin, cycloserine, ciprofloxacin, ofloxacin erythromycin, tetracycline, rifamycins, streptomycin etc.Mechanism of action of antimicrobial drugs
Anti-microbial drugs can act by the inhibition of:Classification of antibiotics
1)β – lactams: Penicillin, Cephalosporins etc.
These antibiotics were found active against gram-positive as well as gram-negative organisms.
2)Oxapenam ring derivatives: Clavulinic acid.
This drug was obtained from Streptomyces clavuligerus which inhibits β – lactamase enzyme and showed its activity against both gram-positive and gram-negative bacteria.
3)Monobactams: Aztreonam.
This drug was obtained from Chromobacter violaceum which was found active against both gram-positive and gram-negative bacteria and was useful mainly for penicillin allergic patients.
4)Carboxypenem: Imipenem.
This drug was obtained from Streptomyces cattleya and was found active against both gram-positive and gram-negative bacteria.
5)Aminoglycosides: Streptomycin, Gentamicin etc.
6)Glycopeptides: Vancomycin.
This drug was obtained from Streptomyces orientales and was found to be nephrotoxic.
7)Lincomycins: Clindamycin.
This drug was obtained from Streptomyces lincolensis and was found active against gram-positive as well as gram-negative bacteria.
8)Polypeptides: Polymyxin, Bacitracin.
9)Polyenes: Amphotericin, Nystatin etc.
10)Rifamycins: Rifampicin.
This drug was obtained from Streptomyces mediterranei and was found active against gram-positive bacteria, gram-negative bacteria and Mycobacterium tuberculosis.
11)Tetracycline: Natural and semi-synthetic bacteria.
This drug was found active against gram-positive bacteria, gram-negative bacteria, ehrlicnia and borrelia. This drug was successfully used in malaria and leprosy.
12)Chloramphenicol: This drug was obtained from Streptomyces venezuelae which was found active against gram-positive bacteria, gram-negative bacteria and used only in life threatening microbial infections. These major adverse effects caused by this drug were bone marrow depression and gray baby syndrome.Development of resistance to antimicrobial drugs
Resistance against antimicrobial drugs may develop due to: