Page 54 - journal-8-2-S-Full

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PP-5

Study on Effect of Downy Myrtle (Rhodomyrtus tomentosa (Aiton.) Hassk )

Leaf Extracts on Some Bacterial Food-Pathogens.

Suhaila Sama-ae, Paiboon Chaosuansreecharoen, Kannika Ruangdej

Sirindhon College of Public Health, Yala, 95000, Thailand.

Rationale: Foodborne infections have been one of the major public health concerns worldwide and ac-
count for considerably high cases of illnesses Some Bacterial Food-Pathogens are commonly distributed in
nature and it can easily contaminate many types of foods. Many attempts such as use of synthetic chemicals
have been made to control microbial growth and to reduce the incidence of foodborne pathogens. Recently,
consumers have grown concerned about the side effects and demand safer materials for preventing and control-
ling pathogenic microorganisms in foods. A wide range of natural antimicrobial substance is being investigated
for food preservation and as food additive to replace chemical agents. Certain antimicrobial substances from
plant origin have good antimicrobial properties. Rhodomyrtus tomentosa (Ait.) Hassk is a genus in the family
Myrtaceae. It is a small shrub, rose-pink flowers and the edible fruits are dark red and bell-shaped. This plant
possesses significant value in herbal medicine.
Objective: To investigate the antibacterial activity of downy myrtle (Rhodomyrtus tomentosa (Aiton.)
Hassk) leaf extracts on some bacterial food-pathogens.
Methodology: The ethanolic leaf extracts from downy myrtle (Rhodomyrtus tomentosa (Ait.) Hassk) was
determined for antibacterial activites on some bacterial food-pathogens. These included Bacillus cereus, Es-
cherichia coli, Listeria monocytogenes, Salmonella sp., Staphylococcus aureus and Vibrio cholerae. Preliminary
screening for their antibacterial activity was evaluated using disc diffusion assay. A modified broth microdilution
method according to guidelines by Clinical and Laboratory Standards Institute was used to determine the MIC
value of the extract. MBC was determined with the extracts that gave significant MIC values by sub-culturing
on fresh medium. The bactericidal actions on some bacterial food-pathogens were assessed at MIC, 2MIC, and
4MIC by counting viable cells after time intervals.
Result: The ethanolic leaf extracts from downy myrtle (Rhodomyrtus tomentosa (Ait.) Hassk) was deter-
mined for antibacterial activities on some bacterial food - pathogens. Preliminary evaluation of antibacterial
activity using paper disk agar diffusion assay using 2.5 mg/disc. Leaf extracts from downy myrtle exhibited
significant antibacterial properties. Minimum inhibitory concentration (MIC) values and minimum bactericidal
concentration (MBC) values of downy myrtle extracts on Bacillus cereus, Staphylococcus aureus, Listeria
monocytogenes, and Vibrio cholerae ranged from 256 - 1,024 and 512- 2,048 μg/ml, respectively. While, MIC and
MBC values of the extracts on Escherichia coli, Salmonella sp. were more than 2,048 μg/ml. The bactericidal
activity of the extract on Bacillus cereus, Staphylococcus aureus, Listeria monocytogenes, and Vibrio cholerae
in nutrient broth were assessed at MIC, 2MIC, and 4MIC by counting viable cells after time intervals. At 4MIC
and 2MIC, the extract killed Bacillus cereus, Staphylococcus aureus and Listeria monocytogenes by at least 3
log cycles within 12 h.
Conclusion: Results obtained in this study indicates that crude extract from downy myrtle (Rhodomyrtus
tomentosa (Ait.) Hassk) produced remarkable activity both gram-positive and gram negative bacteria. It could
be applied as an alternative food additive for controlling some bacterial food pathogens without compromising
the safety of foods.