Explain antimicrobial drugs.

(N/A) Diseases in human beings and animals may be caused by a variety of microorganisms such as bacteria,viruses,fungi,and other pathogens. Antimicrobial drugs are substances used to selectively destroy,prevent the development of,or inhibit the pathogenic action of microbes such as bacteria (antibacterial drugs),fungi (antifungal agents),viruses (antiviral agents),or other parasites (antiparasitic drugs). Antibiotics,antiseptics,and disinfectants are examples of antimicrobial drugs.
$(i)$ Antibiotics: These are chemical substances produced by microorganisms that can destroy or inhibit the growth of other microorganisms due to their low toxicity for humans and animals.
Antibiotics are used as drugs to treat infections. Initially,they were defined as substances produced by microorganisms. However,with the development of synthetic methods,many compounds are now produced wholly or partly by chemical synthesis. An antibiotic now refers to a substance that,in low concentrations,inhibits the growth or destroys microorganisms by intervening in their metabolic processes.
The search for chemicals that would adversely affect invading bacteria but not the host began in the nineteenth century. Paul Ehrlich,a German bacteriologist,developed the first effective treatment for syphilis,known as arsphenamine or salvarsan. He received the Nobel Prize for Medicine in $1908$. Although salvarsan is toxic to humans,its effect on the bacteria (spirochete) causing syphilis is much greater. Ehrlich noted the structural similarity between the $-As=As-$ linkage in arsphenamine and the $-N=N-$ linkage in azodyes,leading him to search for compounds that selectively bind to bacteria.