Control of Bacillus cereus in Foods by Rhodomyrtus tomentosa (Ait.) Hassk. Leaf Extract and Its Purified Compound

Abstract

Edible natural products, either standardized plant extracts or pure compounds, provide unlimited opportunities as safe new antimicrobial agents. This study investigated the antibacterial properties of ethanolic extract from Rhodomyrtus tomentosa (Ait.) Hassk. leaves against Bacillus cereus. Preliminary screening to evaluate the activities of the extract used a paper disc diffusion method against 65 food isolates. The extract produced large inhibition zones in all isolates, ranging from 10 to 18 mm. The results were confirmed by MIC and MBC (16 to 64 and 32 to 256 μg/ml, respectively). Rhodomyrtone, a purified compound, exhibited MIC and MBC at 0.5 and at 2 to 8 μg/ml, respectively. The antimicrobial activity of the extract on vegetative cells and endospores of a representative B. cereus isolate (MIC=32 μg/ml) was assessed by enumerating viable cells at different time intervals up to 24 h. At 2 MICs and 4 MICs, a reduction in the viability of the bacterial cells and endospores was at least 3 log within 6 to 8 h and 2 h after incubation, respectively. Application of the extract in precooked rice and tuna steak demonstrated that after exposure to 16 MICs and 32 MICs, the numbers of viable cells and endospores in both model systems were reduced by at least 2 log within 12 and 6 h, respectively. Since the extract consistently produced remarkable activity against both cells and endospores, it could be used as an alternative food additive for controlling B. cereus without compromising food safety.

Rhodomyrtus Tomentosa: A Phytochemical and Pharmacological Review

“…The crude extract produced large inhibition zones (10.00-18.00 mm) against all tested isolates. The study found that the extract could affect both cells and endospores [35] and suggested the use of the extract as a food preservative or food additive agent for controlling the growth of the pathogen and reducing its incidence. It is believed that the extract would not compromise the safety of food.…”

“…[22] Taraxerol (32) [29] Trans-triacontyl-4-hydroxycinnamate (33) [26] 3,3',4,4'-tetra-O-methylflavellagic acid (34) [26] 3-O-(E)-coumaroyloleanolic acid (35) [26] (-)-(2R,3R)-1,4-O-diferuloylsecoisolariciresinol (36) [26] Arjunolic acid (37) [26] 4-hydroxy-3-methoxybenzoic acid (38) [26] Stigmast-4-en-3-one (39) [26] Oleanolic acid (40) [26] Methyl gallate (41) [26] 3-O-methylellagic acid 4-O-rhamnopyranoside (42) [26] …”

Inhibition of staphyloxanthin biosynthesis in Staphylococcus aureus by rhodomyrtone, a novel antibiotic candidate

“…The compound was isolated from Rhodomyrtus tomentosa (Aiton) Hassk. leaves and exhibits pronounced antibacterial activity against a wide range of Gram-positive bacteria (Limsuwan & Voravuthikunchai, 2008;Saising et al, 2008;Limsuwan et al, 2009a;Voravuthikunchai et al, 2010;Saising et al, 2011). The MIC and minimum bactericidal concentration values of rhodomyrtone against MRSA range from 0.39 to 0.78 mg ml 21 , which is very close to those of vancomycin (Limsuwan et al, 2009b).…”

Use of Rhodomyrtus tomentosa ethanolic leaf extract for the bio-control of Listeria monocytogenes post-cooking contamination in cooked chicken meat

“…Ethanol extract from R. tomentosa leaves has been demonstrated to exhibit excellent potency against a wide range of Gram-positive bacteria (Limsuwan et al 2009a, b), including food related pathogens such as Bacillus cereus (Voravuthikunchai et al 2010), Staphylococcus aureus (Saising et al 2011), and L. monocytogenes (Odedina et al 2015) at low minimum inhibitory concentrations. The extract also showed the ability to reduce B. cereus viable cells and endospores significantly when applied in precooked rice and tuna steak model (Voravuthikunchai et al 2010). …”