331
penicillins, cephalosporins, tetracyclins, etc. Plants and their preparations have also
been considered as rich sources of bioactive compounds as they produce many therapeutically important primary as well as secondary metabolites. Animals of different phyla are proved to be great sources of compounds with antimicrobial properties.
Extracts of various body parts, secretions, and other animal products such as venoms are also explored for such compounds.
13.5.1 Plants
Traditional medicinal preparations, indigenous to different cultures that stood the
test of time, invariably used plants as source of antimicrobial chemotypes. They
have proved effective against infectious diseases and at the same time exhibit very
little or no side effects. Considering their enormous therapeutic potential, plants
need to be studied in greater detail (Tagboto and Townson 2001). Only 10–15% of
higher plants have been investigated and among them only approximately 6% have
been screened for biological activity. This underscores the need for a detailed study
on plant-derived compounds and their role as potential antimicrobials (Borris 1996;
Lucas et al. 2010; Osman et al. 2012). Plants produce a plethora of bioactive compounds called secondary metabolites. Many of these compounds are used in the
development of antimicrobial drugs. These compounds exist in biologically active
or inactive forms in plants. Pathogen attack or tissue damage triggers the biologically inactive molecules and they become active in order to protect the plant from
such adverse conditions (Cowan 1999; Rauha et al. 2000). Three families of phytochemicals are largely known: phenolics, terpenes, and alkaloids; the former being
the largest group of secondary metabolites having exhibited antimicrobial activity.
Phenols, phenolic acids, flavones, flavonoids, coumarins, etc. are examples of subclasses in this group. Some of these molecules are used as drugs while some others
are used as drug precursors, templates for synthetic modification, and pharmacological probes (Salim et al. 2008).
The potential role of phenolic compounds to be used as antimicrobials could be
inferred from the understanding that they are known to protect plants from microbial infections (Saleem et al. 2010). These compounds exhibit different modes of
action for combating microbes. Flavones disrupt bacterial envelopes and catechins
form complexes with bacterial cell wall. The ability of phenolic compounds such as
quinones, anthraquinones, etc. to bind with and cause loss of function of microbial
proteins underlines their therapeutic potential (Kurek et al. 2011; Saleem et al.
2010). Another group of phenolic compounds, tannins, are active against microbes
by their ability to inactivate bacterial adhesins, enzymes, and membrane-bound proteins (Engels et al. 2011). Flavonoids – which are commonly found in plant parts
such as stem, flowers, fruits, and seeds, and plant derivatives such as wine, honey,
etc. – and their derivatives also show excellent antimicrobial activity. Their ability
to bind to form complexes with both extracellular and soluble proteins renders the
bacteria inactive. Detection of anticandidal and antibacterial activity of plantderived flavonoids like angusticornin B and bartericin A (Kuete 2010) makes
13 Novel Sources of Antimicrobials
penicillins, cephalosporins, tetracyclins, etc. Plants and their preparations have also
been considered as rich sources of bioactive compounds as they produce many therapeutically important primary as well as secondary metabolites. Animals of different phyla are proved to be great sources of compounds with antimicrobial properties.
Extracts of various body parts, secretions, and other animal products such as venoms are also explored for such compounds.
13.5.1 Plants
Traditional medicinal preparations, indigenous to different cultures that stood the
test of time, invariably used plants as source of antimicrobial chemotypes. They
have proved effective against infectious diseases and at the same time exhibit very
little or no side effects. Considering their enormous therapeutic potential, plants
need to be studied in greater detail (Tagboto and Townson 2001). Only 10–15% of
higher plants have been investigated and among them only approximately 6% have
been screened for biological activity. This underscores the need for a detailed study
on plant-derived compounds and their role as potential antimicrobials (Borris 1996;
Lucas et al. 2010; Osman et al. 2012). Plants produce a plethora of bioactive compounds called secondary metabolites. Many of these compounds are used in the
development of antimicrobial drugs. These compounds exist in biologically active
or inactive forms in plants. Pathogen attack or tissue damage triggers the biologically inactive molecules and they become active in order to protect the plant from
such adverse conditions (Cowan 1999; Rauha et al. 2000). Three families of phytochemicals are largely known: phenolics, terpenes, and alkaloids; the former being
the largest group of secondary metabolites having exhibited antimicrobial activity.
Phenols, phenolic acids, flavones, flavonoids, coumarins, etc. are examples of subclasses in this group. Some of these molecules are used as drugs while some others
are used as drug precursors, templates for synthetic modification, and pharmacological probes (Salim et al. 2008).
The potential role of phenolic compounds to be used as antimicrobials could be
inferred from the understanding that they are known to protect plants from microbial infections (Saleem et al. 2010). These compounds exhibit different modes of
action for combating microbes. Flavones disrupt bacterial envelopes and catechins
form complexes with bacterial cell wall. The ability of phenolic compounds such as
quinones, anthraquinones, etc. to bind with and cause loss of function of microbial
proteins underlines their therapeutic potential (Kurek et al. 2011; Saleem et al.
2010). Another group of phenolic compounds, tannins, are active against microbes
by their ability to inactivate bacterial adhesins, enzymes, and membrane-bound proteins (Engels et al. 2011). Flavonoids – which are commonly found in plant parts
such as stem, flowers, fruits, and seeds, and plant derivatives such as wine, honey,
etc. – and their derivatives also show excellent antimicrobial activity. Their ability
to bind to form complexes with both extracellular and soluble proteins renders the
bacteria inactive. Detection of anticandidal and antibacterial activity of plantderived flavonoids like angusticornin B and bartericin A (Kuete 2010) makes
13 Novel Sources of Antimicrobials