Aims: This study aimed to determine the antibacterial activity of Piper betle L. leaf extract against Xanthomonas oryzae pv. oryzae that causes bacterial leaf blight in rice plant. Methodology and results: The antibacterial activity of the P. betle leaf extract (100, 50, 25 and 12.25 mg/mL) with four different solvents (methanol, ethyl acetate, hexane and acetone) was evaluated using a disc diffusion assay, minimum inhibitory concentration (MIC) and minimum bactericidal concentration (MBC) values. The inhibition zone of methanolic extract appeared to have the maximum diameter compared to those of other extracts, which is 32.67 mm at a concentration of 100 mg/mL, followed by 30.33 mm, 22.00 mm and 20.30 mm for the concentrations of 50 mg/mL, 25 mg/mL and 12.5 mg/mL, respectively. The MIC and MBC values of the methanolic extract were 0.625 mg/mL suggesting that the extract has a bactericidal effect on X. oryzae pv. oryzae (Xoo). The time-kill curve studies revealed that the 1× MIC (0.625 mg/mL) concentration of methanolic extract had a time and concentration-dependent killing effect on Xoo. Gas chromatography-mass spectrometry (GC-MS) analysis of methanol extract revealed the presence of eugenol acetate (29.53%), 4-allyl-1,2-diacetoxybenzene (29.51%) and 2,3-dimethyl benzoic acid (22.82%) as major compounds. Conclusion, significance and impact of study The methanolic leaf extract of P. betle was proven to have an effective inhibitory effect on Xoo and may have the potential to be used as an alternative management strategy for controlling rice diseases. In the future study, the methanolic leaf extract of P. betle is one of the recommendations to be applied in glasshouse and field trials.
Piper betle ; Oryza--microbiology

Aims: Many plants and their derivatives are widely used in food manufacturing because of their biological activities. They play a significant role as food additives to control microbial growth and the occurrence of oxidation reactions. Syzygium malaccense L. is a well-known plant with biological activities such as antimicrobial and antioxidant activities. Thus, the aims of this study were to evaluate the toxicity of the ethanolic leaves extract of S. malaccense and to study its antibacterial mode of action. Methodology and results: The toxicity assessment of S. malaccense leaves extract was determined using the brine-shrimp larvae model. The action mechanisms against bacterial membrane were determined by studying the intracellular material leakage by means of nucleic acid (DNA and RNA) release, crystal violet dye uptake and cellular protein leakage. The present findings proved the extract's safety as indicated by a high dose of 7.402 mg/mL for lethal concentration (LC50) against brine-shrimp larvae. On the other hand, the ethanolic extract caused a severe membrane permeability towards all the tested bacteria as indicated by the increased intracellular material leakage in a concentration-dependent manner. Conclusion, significance and impact of study The current study provides valuable information regarding the safety and antibacterial action mechanism of S. malaccense ethanolic leaves extract, thus paving the way for its utilization as a natural preservative in a wide range of food products.
Syzygium--toxicity ; Anti-Bacterial Agents

Aims: Jambu batu (Psidium guajava Linn.) is a phytotherapic plant used in folk medicine that has active components to treat various diseases. An earlier study has reported on the analysis of its pharmacological properties and was found to possess antibacterial, antifungal, anti-inflammatory and antioxidant activity. The present study aimed to determine the antibacterial activities of P. guajava Linn. leaves extracts on the vegetative cells of Bacillus cereus ATCC33019, Bacillus megaterium ATCC14581, Bacillus pumilus ATCC14884 and Bacillus subtilis ATCC6633 and to evaluate its effects of different temperatures and pHs on antibacterial activity. Methodology and results: The susceptibility test used to determine the bacterial growth inhibition were well diffusion assay (WDA), minimum inhibitory concentration (MIC), minimum bactericidal concentration (MBC) and time-kill curve assay. The effects of various parameters on temperatures at 10 °C, 28 °C, 30 °C, 50 °C and 80 °C and pH at 3.0, 5.0, 6.7, 7.0 and 11.0 were investigated. WDA assay of the extracts resulted in 13.75 ± 0.95 and 16.25 ± 0.95 mm of inhibition zone on B. subtilis and B. cereus, respectively. The extracts can inhibit the growth with MICs value range of 0.195 to 0.781 mg/mL for B. megaterium and B. pumilus, respectively, and can kill all tested Bacillus spp. with MBCs values of 0.781 mg/mL. The killing time analyses showed that Bacillus spp. can be killed completely within 4 h at 4× MIC (0.781 to 3.124 mg/mL). The extracts remained stable under a wide range of temperatures and pHs, as there was no significant difference in the MIC and MBC values. Conclusion, significance and impact of study Psidium guajava Linn. ethanolic leaves extract yielded good antibacterial activities, suggesting that the extract can be utilised or explored as a potential anti-Bacillus agent in food applications.