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Indian Journal of Dental Research, 24(1), 201371

Antibacterial effect of different concentrations of garlic (Allium sativum) extract on dental plaque bacteria

Behzad Houshmand, Faranak Mahjour, Omid Dianat

Received : 18-07-11Review completed : 19-10-11Accepted : 27-11-11

ABSTRACTBackground: Allium sativum, commonly known as garlic, exhibits antibacterial effects against a wide range of bacteria.Aim: The objective of this in vitro study was to assess the antibacterial effect of different concentrations of garlic extract against human dental plaque microbiota.Materials and Methods: Antibacterial activities of four different concentrations of garlic extract (5%, 10%, 20%, and 100%) were evaluated against Streptococcus mutans, Streptococcus sanguis, Streptococcus salivarius, Pseudomonas aeruginosa, and lactobacillus spp. using the disk diffusion method. Papers soaked in 0.2% concentration chlorhexidine gluconate and saline were used as positive and negative controls, respectively. The data were subjected to one‑way ANOVA and the Tukey multiple comparisons test at a 5% significance level.Results: All bacterial strains were inhibited by all test materials. The inhibition zones of the different concentrations of garlic extract were not significantly different for S. mutans, S. sanguis, and S. salivarius. For P. aeruginosa and lactobacillus spp. the inhibition zones of 5%, 10% and 20% concentrations were not significantly different from one another, but they were significantly more than that of the 100% extract.Conclusion: The 5%, 10%, 20%, and 100% concentrations of garlic extract had similar effects, so further studies seem to be indicated on the usefulness of the 5% extract.

Key words: Allium sativum, antimicrobial effect, dental plaque, garlic extract, oral streptococci

Department of Periodontology, Dental School, Shahid Beheshti University of Medical Sciences, Tehran, Iran

Address for correspondence: Dr. Omid Dianat E‑mail: [email protected]

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DOI: 10.4103/0970-9290.114957

commonly reported undesirable effects of antibiotic usage.[4,5] The side effects of antibiotics, and particularly the increasing problem of antibiotic resistance, emphasizes the need for alternative solutions.

Allium sativum, commonly known as garlic, is one of suggested alternatives to antibiotics, with antibacterial effects against a wide range of bacteria, including Escherichia, Lactobacilli, Helicobacter pylori, Pseudomonas aeruginosa, Klebsiella pneumonia, and Mycobacterium tuberculosis.[6‑11] Streptococcus mutans are responsive to garlic extract, with the minimum inhibition concentration ranging from 4 to 32 µg/ml.[12]

In comparison with tetracycline, pure garlic extract shows more efficient antimicrobial activity against cecal bacteria.[13] Garlic extract also exhibits antifungal and antiviral activity.[14,15] For instance, garlic is reported to an effective fungicidal agent against Candida albicans, a fungus that is usually present in the oral cavity.[16] Garlic is also suggested to act synergistically with antibiotics.[6] These pharmacological properties have been attributed to the presence of allicin and thiosulphonates.[17,18] Elnima et al.[19] have shown that 25% garlic extract has good antimicrobial activity against human oral

Dental plaque is the major cause of dental caries and periodontal disease. Plaque is a habitat for different microorganisms.[1] While plaque removal is necessary for the prevention or treatment of dental caries and periodontal diseases, effective treatment should also ensure reduction of plaque bacteria.[2] The mechanical removal of the plaque is usually inadequate and so chemical agents, generally antibiotics, must also be used in the treatment process.[3] However, antibiotics often have undesirable side effects. Emergence of drug resistance; molecular changes in organisms, which might result in increased virulence; and development of drug hypersensitivity are the most

Original research

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Antibacterial effect of garlic extract on plaque bacteria Hooshmand, et al.

72Indian Journal of Dental Research, 24(1), 2013

microorganisms and have suggested that mouthwash containing 10% garlic extract can significantly reduce the level of oral bacteria.

Not much work has been carried out on the effects of different concentrations of garlic extract. The objective of this in vitro study was to assess the antibacterial effect of different concentrations of garlic extract against human dental plaque microbiota.

MATERIALS AND METHODS

Pure and fresh garlic extract was obtained from Zarband Pharmaceutical Company, Tehran, Iran. According to the manufacturers, the extract was prepared from rootless bulbs of fresh garlic, using an aqueous extraction method. In order to achieve concentrations of 5%, 10%, and 20%, the extract was diluted with sterilized distilled water.

Antibacterial activities of the different concentrations of extract were evaluated against Streptococcus mutans (ATCC 25172), Streptococcus sanguis (ATCC 10566), Streptococcus salivarius (ATCC 25975), Pseudomonas aeruginosa (ATCC 27853), and Lactobacillus spp., using the disk diffusion method. The strains were obtained from the Department of Microbiology, Hamedan Medical University, Hamedan, Iran.

The study was performed on double‑layered plates. The base layer of each plate contained 10 ml of sterilized Muller‑Hinton (MH) agar spread on sterilized petri dishes. Each strain of microorganism was activated and preserved separately in MH broth. All the samples were then incubated at 37°C in the presence of 5% CO2 for 24 h and then, in order to reach a turbidity of 0.5 on the McFarland scale, they were seeded into 15 ml of the MH agar. A total of 20 plates, plus 5 negative controls and 5 positive controls, were used. Filter papers soaked in 0.2% chlorhexidine gluconate (Shahrdaru, Tehran, Iran) and saline were used as positive and negative controls, respectively.

A 6‑mm‑diameter sterilized Whatman filter paper No. 1 (Rundfilter, Macherey‑Nagel, D‑5160 Doren, Germany, Werkstrabe 6‑8) was impregnated with 0.5 ml of the 5%, 10%, 20%, and 100% concentrations of garlic extract and were then located on each plate. The plates were again incubated at 37°C in the presence of 5% CO2 for 72 h. The process was performed under full aseptic conditions.

The diameter of the inhibition areas was determined in millimeters by a neutral observer. Two measurements, perpendicular to each other, were taken for each specimen. The test was repeated thrice, and the mean diameter was determined. The data were subjected to one‑way ANOVA and the Tukey multiple comparisons test at a 5% significance level.

RESULTS

The negative control showed bacterial growth, with no zone of inhibition perceived around the disk. All bacterial strains were inhibited by the positive control as well as all the test materials. The measured mean and standard deviation of the inhibition zones of all samples and positive control after 72 h are shown in Figures 1‑5. It can be seen that the inhibition zones with the different concentrations of garlic extract were not significantly different for S. mutans, S. sanguis, and S. salivarius. For P. aeruginosa and lactobacillus spp. the inhibition zones of 5%, 10% and 20% concentrations were not significantly different from one another, but they were all significantly greater than that of the 100% extract.

DISCUSSION

The aim of this investigation was to evaluate and compare the antibacterial effect of different concentrations of garlic extract against human dental plaque microbiota by using the disk diffusion method. The results of this study reveal that garlic extract at all the different concentrations tested demonstrates antimicrobial activity against plaque microorganisms. Its effect varies with different concentrations and against different microorganisms.

The antibacterial effects of different concentrations of garlic extracts on various strains of bacteria were similar to each other. However, the concentration of 100% of garlic extract was significantly less effective than other concentrations against P. aeruginosa and lactobacillus spp. Furthermore, according to our results the extract is somewhat more effective against lactobacillus spp. than against the other studied bacteria. This observed difference might be a result of genetic differences among the organisms.

A limited number of studies have investigated the antibacterial effects of garlic extract against human dental plaque microbiota. One previous study has reported the significant effect of 10% garlic solution in decreasing levels of oral microorganisms,[19] and our results are in total agreement with this study. Groppo et al.[20] have observed a remarkable reduction of mutans streptococci after gargling with a 2.5% garlic mouthwash solution. Another study, reporting a reduction in levels of S. mutans after garlic mouthwash, mentioned that a 3% concentration was the minimum concentration at which a zone of inhibition was observed.[21] Multidrug‑resistant and non‑multidrug‑resistant strains of S. mutans have also been reported to be sensitive to garlic extract.[12] In addition, combination of garlic with lime is reported to have a noticeable antibacterial effect against isolates from carious teeth.[22] Although these studies were performed using





Figure 1: Zone of inhibition (mean ± standard deviation) of different concentrations of garlic and positive control against S. mutans

Figure 2: Zone of inhibition (mean ± standard deviation) of different concentrations of garlic and positive control against S. sanguis

Figure 3: Zone of inhibition (mean ± standard deviation) of different concentrations of garlic and positive control against S. salivarius

Figure 4: Zone of inhibition (mean ± standard deviation) of different concentrations of garlic and positive control against P. aeruginosa

Figure 5: Zone of inhibition (mean ± standard deviation) of different concentrations of garlic and positive control against Lactobacillus spp

different concentrations from that used in our study, the similarity between our findings and that of other authors is obvious.

Allicin, a phytochemical component of garlic, has been considered to be responsible for the antimicrobial activity

of garlic.[23‑25] This antimicrobial effect of allicin has been attributed to its reactions with the thiol groups of various enzymes, e.g., alcohol dehydrogenase, thioredoxin reductase, and RNA polymerase.[10]

In this study, we compared the antibacterial effect of garlic extract with that of chlorhexidine. Chlorhexidine was more effective than garlic extract but it should be noted that this antimicrobial agent has been known to provoke an immediate hypersensitivity reaction and also has other side effects. For example, chlorhexidine has been reported to be cytotoxic to human periodontal ligament cells.[26] Also, it could hinder protein synthesis and affect mitochondrial activity in these cells.[27] Thus, chlorohexidine could cause serious harm to the oral tissues. In view of this, garlic extract might seem a suitable alternative for many patients.

Recently, there has been an increase in the popularity of herbal medicinal products. A survey revealed that 9.3% of adults use natural health products.[28] Most herbal medicine users have reported that herbs have worked efficaciously for them and, in some instances, been more




74Indian Journal of Dental Research, 24(1), 2013

efficacious than even conventional medicines. Such perceptions might explain the sustained popularity of herbal medicines.[29]

Halitosis, nausea, unpleasant taste,[20] and increased bacterial biofilm formation on orthodontic wire[30] were reported when garlic extract used as a mouth wash. Deodorization of garlic extract may resolve much of these drawbacks. Various methods, including drinking milk[31] and use of mushroom extract,[32] tea catechins, or plant extracts containing polyphenol and phenolic derivatives,[33‑35] have been reported to be effective in suppressing the malodor of garlic.

CONCLUSION

All microorganisms used in the present study were susceptible to the garlic extracts. No isolates were resistant to garlic, indicating that it is a promising antimicrobial agent. The 5%, 10%, 20%, and 100% concentrations of garlic extract had relatively similar effects, so the 5% solution can be considered for further studies. It might be concluded that using optimum concentrations of garlic extract in toothpastes or mouth washes can be useful in the management of dental caries and periodontitis. Clinical studies are necessary to evaluate the efficacy of garlic extract.

ACKNOWLEDGMENTS

The authors are grateful to the Iranian Center for Endodontic Research, Shahid Beheshti University M.C., Tehran, Iran, for technical support.

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How to cite this article: Houshmand B, Mahjour F, Dianat O. Antibacterial effect of different concentrations of garlic (Allium sativum) extract on dental plaque bacteria. Indian J Dent Res 2013;24:71-5.Source of Support: Nil, Conflict of Interest: None declared.

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