Biological Effect of Garlic
Antibacterial Effects
Against Enterohemorrhagic Escherichia coli O157:H7
Food poisoning caused by enterohemorrhagic Escherichia coli O157:H7 was first re-
ported in 1983 by Riley et al. [3]. The symptoms of this unusual gastrointestinal ill-
ness were characterized by the sudden onset of severe abdominal cramps and
bloody diarrhea with no fever or low-grade fever. The illness sometimes develops a
hemolytic uremic syndrome (HUS), which differentiates it from other types of
food poisoning and can often be fatal to the patient, especially in infants.
After the huge outbreak of O157-caused food poisoning in Japan in 1996, spo-
radic outbreaks continued to occur nationwide, and are still reported even now.
This suggests that O157 has already become indigenous to Japan and our sur-
roundings are polluted by this bacterium. O157 is a remarkably resistant organism
that can survive for over three years just in water without any nutrients. It can also
change certain biochemical characters, often leading to microbiological misdiag-
nosis.
We began our study by looking for Japanese foods that have anti-O157 activity,
and soon found that garlic powder was effective [4]. The garlic powder used was
prepared from garlic harvested one year previously. Briefly, garlic bulbs were dried
in the shade for one year, cut into small pieces followed by drying at 60 °C for 6 h,
and grinding into a powder with a mill. Fresh garlic powder was similarly prepared
without air-drying from fresh garlic after harvesting, and used for antibacterial
tests against O157. The antibacterial activity of garlic powder was mainly tested by
the test-tube method, combined with the nutrient agar plate method. Garlic pow-
der easily killed O157 as shown in Table 4.1.
4.2 Garlic 81
Table 4.1 Anti-O157 activity of garlic powder prepared from old or fresh garlic bulbs.
Sample Number of O157 (cfu mL–1)
0 h 6 h 24 h (treatment)
1% Old garlic powder 4.0107 8.0106 0
1% Fresh garlic powder 4.0107 0 0
Control (water alone) 4.0107 8.0107 8.0108
cfu, colony forming unit.
Using the nutrient agar plate test, it was additionally found that garlic powder
killed other species of pathogens, such as methicillin-resistant Staphylococcus aureus
(MRSA), Pseudomonas aeruginosa, Escherichia coli and Bacillus subtilis (Fig. 4.1).
For this test half of the nutrient agar in the Petri dish was replaced by the garlic
powder-supplemented nutrient agar. Then the bacteria were streaked on both
types of agar to examine the growth inhibition activity of the samples.
It is known that the processing of garlic and onion into extracts, essence, and de-
hydrated foods leads to the formation of products with significantly different phy-
sicochemical and biological characteristics [2]. The garlic oil extracted by distilla-
tion in boiling water consists of dimethylsulfides, diallylsulfides, methyl allyl sul-
fides, and others, which have all been shown to process biological properties such
as antioxidant effects. However, it lacks bactericidal and antithrombotic activity.
When garlic is extracted with ethanol and water at room temperature, it yields the
oxide of diallyl disulfide, allicin, which is the source of the garlic odor. Under the
influence of allinase the precursor alliin decomposes to 2-propenesulfenic acid. Al-
licin possesses hypolipidemic, antimicrobial, and hypoglycemic activities [2], and
heat-unstable allicin is considered to be a principal antibacterial constituent [5].
However, as shown in Table 4.2, heat treatment at 100 °C for 20 min could not
eliminate the bactericidal potency and its activity remained in the garlic powder [4].
Thus it seems that garlic contains two types of antibacterial ingredients: the heat-
labile allicin and heat-stable sulfur compounds [6], both of which work together
against bacteria.
82 4 Bioactive Phytocompounds and Products Traditionally Used in Japan
Fig. 4.1 Bactericidal activity of garlic powder
prepared from old garlic bulbs. Pathogenic
bacteria were streaked on both sides of a Petri
dish (upper: control, bottom: 1% (left) and
2% (right) garlic-supplemented). Bacteria
failed to grow on the lower side. From left to
right: Pseudomonas aeruginosa, methicillinresistant
Staphylococcus aureus (MRSA),
Escherichia coli, enterohemorrhagic E. coli
O157, and Bacillus subtilis.
Table 4.2 Thermostability of anti-O157 activity in powder prepared from old garlic bulbs.
Sample Number of O157 (cfu mL–1) after 24 h incubation
1% Garlic powder 0
1% Garlic powder (100 °C, 10 min) 0
1% Garlic powder (100 °C, 20 min) 0
Control (water) 6.2107
cfu, colony forming unit. Garlic powder solution was heat-treated above described conditions.
Antibacterial Effects
Against Enterohemorrhagic Escherichia coli O157:H7
Food poisoning caused by enterohemorrhagic Escherichia coli O157:H7 was first re-
ported in 1983 by Riley et al. [3]. The symptoms of this unusual gastrointestinal ill-
ness were characterized by the sudden onset of severe abdominal cramps and
bloody diarrhea with no fever or low-grade fever. The illness sometimes develops a
hemolytic uremic syndrome (HUS), which differentiates it from other types of
food poisoning and can often be fatal to the patient, especially in infants.
After the huge outbreak of O157-caused food poisoning in Japan in 1996, spo-
radic outbreaks continued to occur nationwide, and are still reported even now.
This suggests that O157 has already become indigenous to Japan and our sur-
roundings are polluted by this bacterium. O157 is a remarkably resistant organism
that can survive for over three years just in water without any nutrients. It can also
change certain biochemical characters, often leading to microbiological misdiag-
nosis.
We began our study by looking for Japanese foods that have anti-O157 activity,
and soon found that garlic powder was effective [4]. The garlic powder used was
prepared from garlic harvested one year previously. Briefly, garlic bulbs were dried
in the shade for one year, cut into small pieces followed by drying at 60 °C for 6 h,
and grinding into a powder with a mill. Fresh garlic powder was similarly prepared
without air-drying from fresh garlic after harvesting, and used for antibacterial
tests against O157. The antibacterial activity of garlic powder was mainly tested by
the test-tube method, combined with the nutrient agar plate method. Garlic pow-
der easily killed O157 as shown in Table 4.1.
4.2 Garlic 81
Table 4.1 Anti-O157 activity of garlic powder prepared from old or fresh garlic bulbs.
Sample Number of O157 (cfu mL–1)
0 h 6 h 24 h (treatment)
1% Old garlic powder 4.0107 8.0106 0
1% Fresh garlic powder 4.0107 0 0
Control (water alone) 4.0107 8.0107 8.0108
cfu, colony forming unit.
Using the nutrient agar plate test, it was additionally found that garlic powder
killed other species of pathogens, such as methicillin-resistant Staphylococcus aureus
(MRSA), Pseudomonas aeruginosa, Escherichia coli and Bacillus subtilis (Fig. 4.1).
For this test half of the nutrient agar in the Petri dish was replaced by the garlic
powder-supplemented nutrient agar. Then the bacteria were streaked on both
types of agar to examine the growth inhibition activity of the samples.
It is known that the processing of garlic and onion into extracts, essence, and de-
hydrated foods leads to the formation of products with significantly different phy-
sicochemical and biological characteristics [2]. The garlic oil extracted by distilla-
tion in boiling water consists of dimethylsulfides, diallylsulfides, methyl allyl sul-
fides, and others, which have all been shown to process biological properties such
as antioxidant effects. However, it lacks bactericidal and antithrombotic activity.
When garlic is extracted with ethanol and water at room temperature, it yields the
oxide of diallyl disulfide, allicin, which is the source of the garlic odor. Under the
influence of allinase the precursor alliin decomposes to 2-propenesulfenic acid. Al-
licin possesses hypolipidemic, antimicrobial, and hypoglycemic activities [2], and
heat-unstable allicin is considered to be a principal antibacterial constituent [5].
However, as shown in Table 4.2, heat treatment at 100 °C for 20 min could not
eliminate the bactericidal potency and its activity remained in the garlic powder [4].
Thus it seems that garlic contains two types of antibacterial ingredients: the heat-
labile allicin and heat-stable sulfur compounds [6], both of which work together
against bacteria.
82 4 Bioactive Phytocompounds and Products Traditionally Used in Japan
Fig. 4.1 Bactericidal activity of garlic powder
prepared from old garlic bulbs. Pathogenic
bacteria were streaked on both sides of a Petri
dish (upper: control, bottom: 1% (left) and
2% (right) garlic-supplemented). Bacteria
failed to grow on the lower side. From left to
right: Pseudomonas aeruginosa, methicillinresistant
Staphylococcus aureus (MRSA),
Escherichia coli, enterohemorrhagic E. coli
O157, and Bacillus subtilis.
Table 4.2 Thermostability of anti-O157 activity in powder prepared from old garlic bulbs.
Sample Number of O157 (cfu mL–1) after 24 h incubation
1% Garlic powder 0
1% Garlic powder (100 °C, 10 min) 0
1% Garlic powder (100 °C, 20 min) 0
Control (water) 6.2107
cfu, colony forming unit. Garlic powder solution was heat-treated above described conditions.
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