Infection can be defined as the multiplication of microbes in the tissues of the host. The host may or may not be symptomatic. Microorganisms can cause diseases without actually come in contact with the host by virtue of toxin production. The pathogenic organisms are highly adapted to the pathogenic state and have developed characteristics that enable them to be transmit, attach to surfaces, invade tissue, avoid host defenses, and thus cause disease.  Approximately 53 million deaths worldwide in 2009, at least a third were due to infectious diseases [1]. Recently, antibiotics and most drugs on the market have shown unwanted symptoms and the emergence of resistant pathogenic microorganisms, toxic effects related to these drugs, and withdrawal issues restricting their use in many countries [2].

Garlic is the most  commonly used food and flavoring agent. When used as a food product, garlic is not  produce any health benefits or side effects. When used as a medicinal product, garlic may produce both desired and unwanted effects in the body. Garlic products sold as health supplements may vary  in the amount of allicin, the active ingredient in garlic. Allicin is unstable and can be reduced in garlic products when they are aged to reduce odor. Odorless garlic may contain little to no allicin. The lower the amount of allicin cause less effectiveness the product might be. Garlic taken orally has been used as alternative medicine in treating high blood pressure, coronary artery disease , circulation problems in the legs, high cholesterol, stomach ulcers caused by H. pylori, stomach cancer, colon cancer , rectal cancer etc.  Garlic applied to the skin is used in treating fungal skin infections like  ringworm, jock itch, or athlete's foot. Preventing the common cold and reversing difficulty urination in patients with prostatomegaly are uses not proved by research till now [3].Garlic is one of the edible part which have generated a lot of interest throughout human history as a medicinal plant. A wide range of microorganisms such as bacteria, fungi, protozoa ,viruses etc  have been shown to be sensitive to crushed garlic preparations [4]. Allicin [S-(2-propenyl)-2-propene-1-sulfinothioate], the most biologically active sulfur-containing compound of garlic, is responsible for its smell and taste [5]. Alliin (S-allyl-L-cysteine sulfoxide) is the main precursor of allicin, which represents about 70% of total thiosulfinates existing in the crushed cloves [6].

       
           
       
Fig. 2

the cooking process . The total amount of saponin in purple garlic was almost 40 times higher than that in white garlic, and several saponin compounds were only found to exist in purple garlic, such as desgalactotigonin-rhamnose, proto-desgalactotigonin, proto-desgalactotigonin- rhamnose, voghieroside D1, sativoside B1-rhamnose, and sativoside R1 . Moreover, garlic contained more than 20 phenolic compounds, with higher contents than many common vegetables . The main phenolic compound was ?-resorcylic acid, followed by pyrogallol, gallic acid, rutin, protocatechuic acid, as well as quercetin [7] . Recently garlic has been proven to be effective against a plethora of gram- positive, gram-negative and acid-fast bacteria and fungi. It has been documented that garlic exerts a differential inhibition between beneficial intestinal microflora and potentially harmful enterobacteria [8]. Garlic contains more than 200 chemical compounds with multiple properties. It is 65% water, 28?rbohydrates, 2.3% organosulfur compounds, 2% proteins, 1.2% free amino-acids, and 1.5% fiber. It also contains fat-soluble vitamins (vitamin A, vitamin K, and vitamin E), water-soluble vitamins (vitamin C, B-complex vitamins: B1, B2, B3, B6, and B8), and minerals (Ca, Fe, Mg, P, K, Na, and Zn). Organosulfur compounds give garlic its characteristic taste and odor as well as its pharmacological properties [9].

Table:1

Antibacterial activity

Various garlic extracts (aqueous, chloroform, methanolic, and ethanolic extracts) were reported to inhibit the growth of several pathogenic bacteria with varying degrees of susceptibility [11]. Allicin’s antimicrobial activity is due to its chemical interaction with enzymes containing thiol e.g., thioredoxin reductase, RNA polymerase, and alcohol dehydrogenase by oxidizing protein cysteine or glutathione residues under physiological conditions [12].

Antifungal activity

The antifungal activity of various A. sativum extracts namely aqueous, ethanolic, methanolic, and petroleum ether against human pathogenic fungi such are Trichophyton verrucosum, T.mmentagrophytes, T.rubrum, Botrytiscinerea, Candida species, Epidermophyton floccosum, Aspergillus niger, A. flavus, Rhizopus stolonifera, Microsporum gypseum, M. audouinii, Alternaria alternate, Neofabraea alba, and Penicillium expansum. The garlic extract acted by affecting the fungal cell wall and causing irreversible ultrastructural changes in the fungal cells, which lead to loss of structural integrity and affected the germination ability. These changes in the cytoplasmic content lead to nucleus and cell organelles damage that ultimately leads to cell death [13].

Antiprotozoal activity

The aqueous, ethanolic, and dichloromethane A. sativum extracts exhibited anthelmintic activity against Haemonchus contortus and the ethanolic extract was the most effective one, while aqueous garlic extract showed potent activity against Trichuris muris and Angiostrongylus cantonensis . Garlic was also examined in vivo and in vitro against Taenia taeniaeformis, Hymenolepis microstoma, H. diminuta, Echinostoma caproni, and Fasciola hepatica [14].

Antiviral activity

 In vivo experiment exhibited the antiviral activity of garlic extract and they reported that garlic showed protective activity against influenza viruses by improving the production of neutralizing antibodies when given to mice and this activity was based on the presence of several phytochemicals namely, ajoene, allicin, allyl methyl thiosulfinate, and methyl allyl thiosulfinate. Allicin acts by preventing several thiol enzymes, while ajoene’s antiviral activity was due to the prevention of adhesive interaction and fusion of leukocytes [15].

Disc diffusion method

Disc diffusion by the Kirby-Bauer method is a standardized technique for testing rapidly growing pathogens. It is the most flexible antimicrobial susceptibility testing method. The method consists of placing paper disks saturated with antimicrobial agents on a lawn of bacteria seeded on the surface of an agar medium, incubating the plate overnight, and measuring the presence or absence of a zone of inhibition around the discs. Because reproducibility depends on the log growth phase of organisms, fresh subcultures are used. Filter paper disks impregnated with a standardized concentration of an antimicrobial agent are placed on the surface, and the size of the zone of inhibition around the disk is measured after overnight incubation [16].

MATERIALS AND METHODS

Plant Material: The garlic bulb was collected from Payangadi town of Kerala during the month of December and authentified by botanist.

Bacterial strain

Escherichia Coli were used in the study. Pure culture was collected from Government Medical College, Pariyaram, Kannur, Kerala.

Preparation of Extract: The garlic bulb (150gm) was peeled, washed with distilled water thoroughly. 100 gm of garlic was weighed and partially crushed using clean mortar and pestle, 10 ml of distilled water was added to it and homogenized again with mortar and pestle and filtered through a clean muslin cloth. To this residue 5 ml distilled water was added and filtered again. The ethanolic extract was prepared using the same procedure with the exception of solvent which was 95% ethanol instead of distilled water. All the extracts were stored in a refrigerator.

Phytochemical screening

The extracts of Allium sativum bulb  was analyzed for the presence of phytochemical constituents such as steroids, triterpinoids, carbohydrates, alkaloids, glycosides, phenolic compounds, flavonoids, saponins, tannins, amino acids and sulphur with the standard qualitative phytochemical methods.

Table : 2

Antimicrobial Screening

Preparation of nutrient broth

Suspend 8.4 grams  of  Muller Hinton agar in 300 ml of distilled water.  Add 2.5 mg of agar-agar as a solidifying agent. Autoclave the  mixture at 121⁰C for 15 minutes. Once the nutrient agar has been autoclaved , allow it to cool but not solidify. When temperature reduces to 40⁰C transfer a pure culture of organism to the agar broth. Pour the nutrient agar into 5 different petri dishes and leave the plates on a sterile surface until the agar has solidified.

Preparation of standard drug solution

Ciprofloxacin tablets (500mg) were powdered using a mortar and pestle.1g of the powdered tablets was weighed and dissolved in 100ml of distilled water.1ml of this solution was pipette out and transferred into a 10ml volumetric flask. The flask was then filled up to the 10 ml mark with distilled water.

Preparation of discs

Sterilize filter paper discs by autoclaving them at 121⁰C for 15 minutes. Immerse the sterilized discs in the aqueous extract of Allium sativum. Immerse another set of discs in the ethanolic extract of Allium sativum. Soak other sets of discs in the Ciprofloxacin solution and soak the remaining discs in distilled water as a control. Allow the soaked discs to dry.

Disc diffusion method

Using sterile forceps, each disc is placed on the surface of  the inoculated and dried plate. Without moving the disc, fix it lightly to ensure complete contact. The disc should be positioned so that the minimum center-center distance is 24 mm and no closer than 10 to 15 mm from the edge of the petri dish. Four petri plates were prepared : Petri plate A (Ethanolic extract), Petri plate B (Aqueous  extract), Petri plate C (Ciprofloxacin) and  Petri plate D (control). All four prepared petri plates were observed for zone of inhibition is measured by using ordinary ruler.

Table:3

       
           
       
 DISCUSSION