MEDICINAL PLANTS AS A
SOURCE OF ANTIMICROBIAL
AGENTS
Under supervision
PROF.DR.Mohamed Hisham EL Masry
By
Wesam Said Ebrahim
BRIEF HISTORY
Hippocrates (in the late fifth century B.C.)
mentioned 300 to 400 medicinal plants
 Dioscorides wrote De Materia Medica, a
medicinal plant catalog
 The Bible offers descriptions of approximately
30 healing plants
 During the Dark Ages,the Arab world continued
to excavate their own older works and to build
upon them.

MAJOR GROUPS OF ANTIMICROBIAL
COMPOUNDS FROM PLANTS
PLANTS HAVE ANTIMICROBIAL ACTIVITY

Allium cepa
(onion)

Allium sativum
(garlic)
PLANTS HAVE ANTIMICROBIAL ACTIVITY

Aloe vera
(aloe)
PLANTS HAVE ANTIMICROBIAL ACTIVITY

Camellia sinensis
(green tea)
 Capsicum
annuum
(chili peppers)
PLANTS HAVE ANTIMICROBIAL ACTIVITY

Carum carvi(Caraway)

Cinnamomum verum
(Ceylon cinnamon)
PLANTS HAVE ANTIMICROBIAL ACTIVITY

Lawsonia inermis
(henna)

Matricaria chamomilla
(chamomile)
PLANTS HAVE ANTIMICROBIAL ACTIVITY

Olea europaea
(Olive oil)

Vicia faba
(Fava bean)
Scientific name
Allium cepa
Allium sativum
Aloe barbadensis,
Aloe vera
Anacardium pulsatilla
Camellia sinensis
Common name
Compound
Class
Activity
Onion
Allicin
Sulfoxide
Bacteria, Candida
Garlic
Allicin, ajoene
Aloe
Latex
Complex mixture
Cashew
Salicylic acids
Polyphenols
Green tea
Catechin
Flavonoid
Sulfoxide, Sulfated
terpenoids
General
Corynebacterium,
Salmonella, Streptococcus,
S. aureus
P. acnes
Bacteria, fungi
General ,Shigella Vibrio ,
S. mutans
Viruses
Capsicum annuum
Carum carvi
Cinnamomum verum
Lawsonia inermis
Chili peppers, paprika
Capsaicin
Caraway
Terpenoid
Bacteria
Coumarins
Bacteria, fungi, viruses
Ceylon cinnamon
Essential oils,
others
Terpenoids, tannins
General
Henna
Gallic acid
Phenolic
S. aureus
Phenolic acid
M. tuberculosis,
S. typhimurium,
S. aureus,
Matricaria chamomilla
Chamomile
Anthemic acid
helminths
Olea europaea
Olive oil
Hexanal
Thyme
Caffeic acid
Thymol
Tannins
Thymus vulgaris
Vicia faba
Fava bean
Fabatin
Aldehyde
General
Terpenoid
Phenolic alcohol
Polyphenols
Viruses, bacteria, fungi
Flavones
Thionin
Plants containing antimicrobial activity
Bacteria
MAJOR GROUPS OF ANTIMICROBIAL
COMPOUNDS FROM PLANTS
Plants have an almost limitless ability to
synthesize aromatic substances
 these substances serve as:
plant defense mechanisms against predation by
microorganisms, insects, and herbivores.
Some, such as terpenoids, give plants their odors;
others (quinones and tannins) are responsible for
plant pigment.
Many compounds are responsible for plant flavor
(e.g., the terpenoid capsaicin from chili peppers)

MAJOR GROUPS OF ANTIMICROBIAL
COMPOUNDS FROM PLANTS
Phenolics and Polyphenols
 Terpenoids and Essential Oils
 Alkaloids
 Lectins and Polypeptides
 Mixtures

PHENOLICS AND POLYPHENOLS
1-Simple phenols and phenolic acids.
 2-Quinones
 3-Flavones, flavonoids, and flavonols
 4-Tannins.
 5-Coumarins.

PHENOLICS AND POLYPHENOLS
1-Simple phenols and phenolic acids
 the simplest bioactive phytochemicals consist
of a single substituted phenolic ring.
Ex.

Cinnamic and caffeic acids( in tarragon and
thyme ) , which is effective against viruses,
bacteria,and fungi.
PHENOLICS AND POLYPHENOLS

Catechol (2 OH )and pyrogallol (3OH) both are
hydroxylated phenols, shown to be toxic to
microorganisms.
Catechol (2 OH )


OH
pyrogallol (3OH)
Toxicity
The mechanisms thought to be responsible for phenolic
toxicity to microorganisms include enzyme inhibition
PHENOLICS AND POLYPHENOLS
2-Quinones
 aromatic rings with two ketone substitutions
 highly reactive
 Colored
 responsible for the browning reaction
in cut or injured fruits and vegetables
 are an intermediate in the melanin synthesis
pathway in human skin
THE MELANIN SYNTHESIS PATHWAY IN HUMAN
SKIN
PHENOLICS AND POLYPHENOLS
ex
Hypericin (Hypericum perforatum)
antidepressant, and has antimicrobial
properties
PHENOLICS AND POLYPHENOLS
3-Flavones, flavonoids, and flavonols
 Flavones are phenolic structures containing
one carbonyl group
 flavonol = flavones + 3-hydroxyl group
 Flavonoids are also hydroxylated phenolic
substances but occur as a C6-C3 unit linked to
an aromatic ring.
Flavone
Flavonol
PHENOLICS AND POLYPHENOLS
3-Flavones, flavonoids, and flavonols
 synthesized by plants in response to microbial
infection
 effective antimicrobial substances against a
wide array of microorganisms.
 Mechanism complex with extracellular and
soluble proteins and complex with bacterial cell
walls
PHENOLICS AND POLYPHENOLS
ex
Catechins in green teas
inhibited in vitro Vibrio cholerae O1,
Streptococcus mutans, Shigella,
and other bacteria and microorganisms

in vivo tests of conventional rats,the rats were
fed a diet containing 0.1% tea catechins,
fissure caries (caused by S. mutans) was
reduced by 40%
PHENOLICS AND POLYPHENOLS
4-Tannins.
 polymeric phenolic substances
 tanning leather or precipitating gelatin from
solution
 complex with proteins through so-called
nonspecific forces such as hydrogen bonding
and hydrophobic effects
PHENOLICS AND POLYPHENOLS

Tannis inhibit insect growth and disrupt
digestive events in ruminal animals (in plants)

toxic to filamentous fungi, yeasts,and bacteria

Condensed tannins have been determined to
bind cell walls of ruminal bacteria, preventing
growth and protease activity
PHENOLICS AND POLYPHENOLS
5-Coumarins
 Coumarins are phenolic substances made of
fused benzene and a-pyrone rings
 Warfarin is a particularly well-known coumarin
which is used both as an oral anticoagulant
and, interestingly,as a rodenticide & also have
antiviral effects
TERPENOIDS AND ESSENTIAL OILS
Terpenes general chemical structure is
C10H16, and they occur as diterpenes,
triterpenes, and tetraterpenes (C20, C30, and
C40)
 additional elements, usually oxygen+ Terpenes
= terpenoids
ex Camphor (monoterpenes)
 Terpenenes or terpenoids are active against
bacteria ,fungi ,viruses ,and protozoa

ALKALOIDS

Heterocyclic nitrogen compounds

alkaloids, commonly isolated from the plants of
the Ranunculaceae family are commonly found
to have antimicrobial properties .
LECTINS AND POLYPEPTIDES

Peptides which are inhibitory to
microorganisms were first reported in 1942

Their mechanism of action may be the
formation of ion channels in the microbial
membrane or competitive inhibition of
adhesion of microbial proteins to host
polysaccharide receptors
Polypeptides mechanism of action
LECTINS AND POLYPEPTIDES

Lectins are proteins or glycoprotiens

Both have antibacterial and
antifungal activity
Ricin
MIXTURES
chewing stick
 within one stick the chemically active
component may be heterogeneous
 The active component of the Nigerian chewing
stick (Fagara zanthoxyloides) was found to
consist of various alkaloids