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temperature and pH normally inaccessible to advanced higher organisms. Human
beings are also included in the natural habitat of microorganisms. They inhabit the
skin, mucous layers, and the gastrointestinal tract of humans. Most of the human
microflora are nonpathogenic symbionts, and many of them endow the host with
numerous benefits, including a defense mechanism against the invasion by foreign
microbes. These microorganisms have coexisted with the human system for thousands of years and have learned to settle amicably inside it. But many microbes do
not render this favor to human beings. They access and survive in the human system
by causing serious damages to the host and are collectively called infectious microorganisms. Yet another group called the opportunistic pathogens normally inhabits
humans asymptomatically but causes diseases when an opportunity arises. The fight
against infective microorganisms had always been a primary goal of the biologists.
With the advent of modern science, systematic control measures were sought
against microorganisms. Synthetic azo dyes were discovered to have potential to
inhibit the growth of microorganisms. The discovery of penicillin in 1928 opened
up an entirely new arena in the fight against microorganisms. Incidentally, the antimicrobial substance penicillin was discovered from another microorganism, a fungus called Penicillium notatum. This discovery initiated the search for antimicrobial
substances from natural sources including microorganisms. These substances find
applications not only against microorganisms infecting human beings but also
against those infecting domesticated and economically important animals and
plants. Advances in the science of microbiology, fermentation technology and combinatorial chemistry greatly facilitated the search for novel antimicrobial compound
from microorganisms. Initially, during the so-called golden era of antibiotics, it
appeared that humans have won the fight against infective microorganisms. But it
did not take much for microbial pathogens to counteract the antimicrobials used
against them by developing mutated molecules and processes that offered them
resistance to antimicrobials. Moreover, the discovery of antimicrobials from microorganisms reached a level of saturation in the 1960s. Now the focus has shifted to
identify hitherto unknown classes of microbial metabolites that target novel molecules or pathways in microorganisms that do not provide them opportunity to
develop resistance. For instance, antimicrobials targeting lipids involved in cell
wall synthesis are well sought for targets as lipids do not develop mutations the way
proteins do. Untapped but potential sources such as uncultured microorganisms are
now targeted for novel antimicrobials. This chapter explores the important antimicrobial molecules isolated from microorganisms.
12.2 Antimicrobials
Antimicrobials can be defined as any substance of natural, semisynthetic or synthetic origin that inhibits the growth of microorganisms. The term antimicrobial
covers different classes of substances including disinfectants, antiseptics and antibiotics. Disinfectants are antimicrobials that are applied to nonliving surfaces to
inhibit the growth of microorganisms. Antiseptics are applied topically on living
D. Francis
temperature and pH normally inaccessible to advanced higher organisms. Human
beings are also included in the natural habitat of microorganisms. They inhabit the
skin, mucous layers, and the gastrointestinal tract of humans. Most of the human
microflora are nonpathogenic symbionts, and many of them endow the host with
numerous benefits, including a defense mechanism against the invasion by foreign
microbes. These microorganisms have coexisted with the human system for thousands of years and have learned to settle amicably inside it. But many microbes do
not render this favor to human beings. They access and survive in the human system
by causing serious damages to the host and are collectively called infectious microorganisms. Yet another group called the opportunistic pathogens normally inhabits
humans asymptomatically but causes diseases when an opportunity arises. The fight
against infective microorganisms had always been a primary goal of the biologists.
With the advent of modern science, systematic control measures were sought
against microorganisms. Synthetic azo dyes were discovered to have potential to
inhibit the growth of microorganisms. The discovery of penicillin in 1928 opened
up an entirely new arena in the fight against microorganisms. Incidentally, the antimicrobial substance penicillin was discovered from another microorganism, a fungus called Penicillium notatum. This discovery initiated the search for antimicrobial
substances from natural sources including microorganisms. These substances find
applications not only against microorganisms infecting human beings but also
against those infecting domesticated and economically important animals and
plants. Advances in the science of microbiology, fermentation technology and combinatorial chemistry greatly facilitated the search for novel antimicrobial compound
from microorganisms. Initially, during the so-called golden era of antibiotics, it
appeared that humans have won the fight against infective microorganisms. But it
did not take much for microbial pathogens to counteract the antimicrobials used
against them by developing mutated molecules and processes that offered them
resistance to antimicrobials. Moreover, the discovery of antimicrobials from microorganisms reached a level of saturation in the 1960s. Now the focus has shifted to
identify hitherto unknown classes of microbial metabolites that target novel molecules or pathways in microorganisms that do not provide them opportunity to
develop resistance. For instance, antimicrobials targeting lipids involved in cell
wall synthesis are well sought for targets as lipids do not develop mutations the way
proteins do. Untapped but potential sources such as uncultured microorganisms are
now targeted for novel antimicrobials. This chapter explores the important antimicrobial molecules isolated from microorganisms.
12.2 Antimicrobials
Antimicrobials can be defined as any substance of natural, semisynthetic or synthetic origin that inhibits the growth of microorganisms. The term antimicrobial
covers different classes of substances including disinfectants, antiseptics and antibiotics. Disinfectants are antimicrobials that are applied to nonliving surfaces to
inhibit the growth of microorganisms. Antiseptics are applied topically on living
D. Francis