Model 1240

The selected bacteria were used to evaluate the antibacterial activity of the crude extracts of Barringtonia asiatica, Salmonella typhi, Escherichia coli, Staphylococcus aureus, and Klebsielia pneumoniae were obtained from the stock culture provided by Virology Laboratory, Universiti Malaysia Sarawak. The nutrient broth was prepared according to the manufacturer's instruction, with 2.6 g of the dried broth dissolved in 200 mL distilled water followed by sterilization in an autoclave at 121°C. The bacteria was subcultured in 10 mL of broth, each in universal glass vail bottle for 16 hours inside an incubator equipped with a shaker at 37°C [23 ]. After 16 hours' incubation, turbidity (optical density/OD) of the bacterial broth was measured by using UV minispectrophotometer (model 1240 of Shimadzu brand), which is comparable to that of the nutrient broth standard tube for further use [24 ]. The measurement of the optical density was performed at wavelength 575 nm, and the bacterial broth was ready to be used when its turbidity was between OD 0.6 to 0.9. Nutrient broth was used to adjust the turbidity until the desired value was obtained.

The determination of total phenol content was carried out in triplicate, according to the Folin–Ciocaulteu method [125 (link)], using gallic acid (Sigma Aldrich, Berlin, Germany) as standard. The reaction took place in a water bath at 50 °C (20 min) and was read on a UV-Vis spectrophotometer, model 1240 Shimadzu, λ = 760 nm. Samples were analyzed at a concentration of 25 μg mL⁻¹.