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11.1 Introduction
Plants act as an attractive source of antimicrobial agents. The study of medicinal
plants as antimicrobial agents is indispensable for gaining insight into the real value
of medicinal flora. The traditional use of medicinal plants is useful as a guideline in
the search for new drugs. Moreover, plants are a source of novel lead compounds
which would normally not have been synthesized. Isolation of these biologically
active lead compounds is a slow and expensive process. The therapeutic potential of
these compounds should be periodically reviewed, and it must be clinically proven
in order to accelerate the drug discovery process. Likewise, research in this area
should be carried on till the agent responsible for the activity has been identified.
Pharmaceutical sector is looking for unique drug candidates to manage microbial
infections. Many phytochemicals and plant extracts are already reported as potent
antimicrobials when used alone or as synergists of other antibacterial agents.
Infections caused by multidrug-resistant bacteria raise an alarming situation due to
the shortage of newly developed promising antibiotic candidates. Traditional methods employed for the discovery of antibiotics are futile to keep pace with the rate of
evolution of drug resistance. The problem of drug resistance necessitates the search
for novel lead molecules that target vital proteins in the prokaryotic system.
Secondary metabolites in plants form the defence system which fights against predators like herbivores, insects and microorganisms. Plant secondary metabolites act
by different mechanisms than conventional antibiotics, and thus it can be utilized in
the treatment of resistant bacteria. Pharmacokinetic parameters such as bioavailability and capacity to bind plasma protein are also important characteristics of
plant secondary metabolites. New drug targets in the bacterial structure are also
important in beating the resistant strains as it will be more effective if a drug has
several modes of action.
11.2 Antimicrobial Compounds
The beneficial medicinal properties of plants characteristically result from the combinations of several compounds present in them. In plants, these compounds are
mainly secondary metabolites such as alkaloids, tannins and other phenolic compounds, which are localized in specific parts or in all parts of the plant. Mostly, these
phytochemicals serve as plant defence mechanisms against predators and microbes.
Some, like quinones and tannins, give pigmentation to plants, others, like terpenoids, impart plants in their odours, and some other compounds are associated with
flavour and aroma. Figure 11.1 shows the chemical structures of some important
classes of antimicrobial plant metabolites.
Detailed information on the chemical nature and pharmacological activity of
some of these classes are given below.
R. Reghu et al.
11.1 Introduction
Plants act as an attractive source of antimicrobial agents. The study of medicinal
plants as antimicrobial agents is indispensable for gaining insight into the real value
of medicinal flora. The traditional use of medicinal plants is useful as a guideline in
the search for new drugs. Moreover, plants are a source of novel lead compounds
which would normally not have been synthesized. Isolation of these biologically
active lead compounds is a slow and expensive process. The therapeutic potential of
these compounds should be periodically reviewed, and it must be clinically proven
in order to accelerate the drug discovery process. Likewise, research in this area
should be carried on till the agent responsible for the activity has been identified.
Pharmaceutical sector is looking for unique drug candidates to manage microbial
infections. Many phytochemicals and plant extracts are already reported as potent
antimicrobials when used alone or as synergists of other antibacterial agents.
Infections caused by multidrug-resistant bacteria raise an alarming situation due to
the shortage of newly developed promising antibiotic candidates. Traditional methods employed for the discovery of antibiotics are futile to keep pace with the rate of
evolution of drug resistance. The problem of drug resistance necessitates the search
for novel lead molecules that target vital proteins in the prokaryotic system.
Secondary metabolites in plants form the defence system which fights against predators like herbivores, insects and microorganisms. Plant secondary metabolites act
by different mechanisms than conventional antibiotics, and thus it can be utilized in
the treatment of resistant bacteria. Pharmacokinetic parameters such as bioavailability and capacity to bind plasma protein are also important characteristics of
plant secondary metabolites. New drug targets in the bacterial structure are also
important in beating the resistant strains as it will be more effective if a drug has
several modes of action.
11.2 Antimicrobial Compounds
The beneficial medicinal properties of plants characteristically result from the combinations of several compounds present in them. In plants, these compounds are
mainly secondary metabolites such as alkaloids, tannins and other phenolic compounds, which are localized in specific parts or in all parts of the plant. Mostly, these
phytochemicals serve as plant defence mechanisms against predators and microbes.
Some, like quinones and tannins, give pigmentation to plants, others, like terpenoids, impart plants in their odours, and some other compounds are associated with
flavour and aroma. Figure 11.1 shows the chemical structures of some important
classes of antimicrobial plant metabolites.
Detailed information on the chemical nature and pharmacological activity of
some of these classes are given below.
R. Reghu et al.