332
flavonoids suitable candidate molecules for drug development. Flavonoids from the
leaf extract of Leiothrix spiralis are shown to be effective against E. coli and P.
aeruginosa (Araujo et al. 2011). Alkaloids, on the other hand, attack bacteria by
acting as a DNA intercalating agent or by inhibiting enzymes such as RNA polymerase, DNA gyrase, and topoisomerase IV (Yi et al. 2007).
Essential oils from plants are a great source of antimicrobials. Antibacterial,
antifungal, and antiviral properties of essential oils containing volatile substances
such as monoterpenes, sesquiterpenes, and/or phenylproanoids are reported
(Prabuseenivasan et al. 2006). Both phenolic and nonphenolic compounds of essential oils are found effective against various pathogens. Phenolic compounds of
essential oils such as oleuropein (olive oil), terpenoids (tea-tree oil), etc. have
broader antimicrobial effects. Nonphenolic oil compounds present in lemongrass,
rosemary, garlic, clove, cinnamon, etc. show promising antibacterial activity on
both Gram positive and Gram negative organisms (Gutierrez et al. 2008, Holley and
Patel 2005; Mandalari et al. 2007). Other nonphenolic constituents of essential oils
such as allyl thiocyanate and allyl isothiocyanate are proved to be effective against
Gram negative bacteria and many fungi (Nielsen and Rios 2000; Yin and Cheng
2003). Other secondary metabolites such as terpenes, steroids, polyketides, peptides, etc. are also considered to be brilliant candidates for antimicrobial therapeutic
development with their proven ability to act even against multidrug-resistant M.
tuberculosis (Garcia et al. 2012). Natural resins derived from plants belonging to
various families including Euphorbiaceae, Apiaceae, Burseraceae, Fabaceae, etc.
and their specific extracts and compounds isolated from them are suggested to have
potential antimicrobial activities. They are found to be active against different types
of microorganisms including bacteria, fungi, and protozoan parasites (Termentzi
et al. 2011). Since such plants have been used successfully in traditional medicine
for centuries, it is never too far from getting therapeutically active compounds isolated from them. Technological advancements and focused screening programs conducted in this field would function together toward this goal (Savoia 2012).
Endophytes are organisms that live inside (Greek: Endo) a plant (Greek: Phyte)
for at least a part of their life (Wilson 1995). Since the endophytes are nonpathogenic fungi and bacteria, they are rightly considered endosymbionts. Ecomycins,
pseudomycins, munumbicins, and xiamycins are examples of endophyte-derived
compounds having antimicrobial effects (Christina et al. 2013). Among them, ecomycins and pseudomycins are two families of peptide antimycotics which are
proved to be very active against Cryptococcus neoformans and Candida albicans
(Harrison et al. 1991). The other two classes of antibiotics are derived from
Streptomyces spp.; the former is a wide-spectrum antibiotic and the latter is shown
to have anti-HIV activity (Castillo et al. 2002; Ding et al. 2010).
Antimicrobial peptides (AMPs) or host defence peptides (HDPs) are small peptides (6–50 amino acids) having net positive charge (Bradshaw 2003; Hancock and
Patrzykat 2002) that are part of the innate immune response. AMPs derived from
plants is yet another interesting class of molecules having antimicrobial activities.
They are shown to be active against plant pathogens as well as bacteria pathogenic
to humans (Montesions and Bardaji 2008). AMPs are diverse peptides and they
Lini Nirmala and D.P. Zyju
flavonoids suitable candidate molecules for drug development. Flavonoids from the
leaf extract of Leiothrix spiralis are shown to be effective against E. coli and P.
aeruginosa (Araujo et al. 2011). Alkaloids, on the other hand, attack bacteria by
acting as a DNA intercalating agent or by inhibiting enzymes such as RNA polymerase, DNA gyrase, and topoisomerase IV (Yi et al. 2007).
Essential oils from plants are a great source of antimicrobials. Antibacterial,
antifungal, and antiviral properties of essential oils containing volatile substances
such as monoterpenes, sesquiterpenes, and/or phenylproanoids are reported
(Prabuseenivasan et al. 2006). Both phenolic and nonphenolic compounds of essential oils are found effective against various pathogens. Phenolic compounds of
essential oils such as oleuropein (olive oil), terpenoids (tea-tree oil), etc. have
broader antimicrobial effects. Nonphenolic oil compounds present in lemongrass,
rosemary, garlic, clove, cinnamon, etc. show promising antibacterial activity on
both Gram positive and Gram negative organisms (Gutierrez et al. 2008, Holley and
Patel 2005; Mandalari et al. 2007). Other nonphenolic constituents of essential oils
such as allyl thiocyanate and allyl isothiocyanate are proved to be effective against
Gram negative bacteria and many fungi (Nielsen and Rios 2000; Yin and Cheng
2003). Other secondary metabolites such as terpenes, steroids, polyketides, peptides, etc. are also considered to be brilliant candidates for antimicrobial therapeutic
development with their proven ability to act even against multidrug-resistant M.
tuberculosis (Garcia et al. 2012). Natural resins derived from plants belonging to
various families including Euphorbiaceae, Apiaceae, Burseraceae, Fabaceae, etc.
and their specific extracts and compounds isolated from them are suggested to have
potential antimicrobial activities. They are found to be active against different types
of microorganisms including bacteria, fungi, and protozoan parasites (Termentzi
et al. 2011). Since such plants have been used successfully in traditional medicine
for centuries, it is never too far from getting therapeutically active compounds isolated from them. Technological advancements and focused screening programs conducted in this field would function together toward this goal (Savoia 2012).
Endophytes are organisms that live inside (Greek: Endo) a plant (Greek: Phyte)
for at least a part of their life (Wilson 1995). Since the endophytes are nonpathogenic fungi and bacteria, they are rightly considered endosymbionts. Ecomycins,
pseudomycins, munumbicins, and xiamycins are examples of endophyte-derived
compounds having antimicrobial effects (Christina et al. 2013). Among them, ecomycins and pseudomycins are two families of peptide antimycotics which are
proved to be very active against Cryptococcus neoformans and Candida albicans
(Harrison et al. 1991). The other two classes of antibiotics are derived from
Streptomyces spp.; the former is a wide-spectrum antibiotic and the latter is shown
to have anti-HIV activity (Castillo et al. 2002; Ding et al. 2010).
Antimicrobial peptides (AMPs) or host defence peptides (HDPs) are small peptides (6–50 amino acids) having net positive charge (Bradshaw 2003; Hancock and
Patrzykat 2002) that are part of the innate immune response. AMPs derived from
plants is yet another interesting class of molecules having antimicrobial activities.
They are shown to be active against plant pathogens as well as bacteria pathogenic
to humans (Montesions and Bardaji 2008). AMPs are diverse peptides and they
Lini Nirmala and D.P. Zyju