Antimicrobial Activity and Mechanism of Action of the Amaranthus tricolor Crude Extract against Staphylococcus aureus and Potential Application in Cooked Meat

Abstract

Amaranthus tricolor has been reported to contain some antimicrobial compounds, such as alkaloids, polyphenols, and terpenoids. However, its effect on Staphylococcus aureus has been less well researched. Therefore, this study was designed to evaluate the antimicrobial activity and possible mechanism of action of the Amaranthus tricolor crude extract (ATCE) against S. aureus and potential application in cooked meat. The antimicrobial activity against S. aureus was assessed by disk diffusion, minimum inhibitory concentration (MIC) determinations, and growth curve. The changes of bacterial membrane potential, intracellular pH (pHin), content of bacterial protein and DNA, and cell morphology were measured to indicate its antimicrobial mechanism of action. The effects of different concentrations of ATCE on bacterial counts, pH, and color of lean cooked pork during 6 d storage were assessed. The results showed that the diameter of inhibition zone (DIZ) and MIC of ATCE against S. aureus were 12.63 ± 0.34 to 12.94 ± 0.43 mm and 80 mg/mL, respectively. The mechanism of action of ATCE against S. aureus was associated with cell membrane depolarization, reduction of pHin, decrease of bacterial protein content, cleavage of cell DNA, and leakage of cytoplasm. Besides, ATCE resulted in a reduction of 1.02 log CFU/g from 3 log CFU/g in S. aureus-inoculated lean cooked pork. The pH values of lean cooked pork treated with ATCE did not show significant changes as the storage time increased, but there was a slight and significant decrease seen with the application of 1 and 2 MIC of ATCE. After treating with ATCE, the color of lean cooked pork showed less lightness (L*), more redness (a∗), similar yellowness (b*), stronger chroma (C*), and weaker hue angle (h*) during 6 days of storage. Therefore, these findings indicate that ATCE has antimicrobial activities against S. aureus and possesses latent energy to become a natural preservative to maintain the quality of lean cooked pork.

Antibacterial Activity of Chrysanthemum buds Crude Extract Against Cronobacter sakazakii and Its Application as a Natural Disinfectant

“…In the current study, the cell membrane depolarization was found in the C. sakazakii strains after treatment with CBCE. Similar results have been reported in previous studies on the bacteriostatic process on nopal cactus methanolic extracts against Vibrio cholerae , lipoic acid against C. sakazakii , and ATCE against Staphylococcus aureus ( Sánchez et al, 2010 ; Shi et al, 2016c ; Guo L. et al, 2020 ). As a comparison, the cell membrane hyperpolarization was observed in the C. sakazakii cells treated by citral and syringic acid ( Shi et al, 2016a,b ).…”

“…Previous studies have taken the change in bacterial protein as one of the important ways to reveal the antibacterial mechanism of natural products and found that the bacterial protein of the tested bacteria significantly decreased after the treatments with natural products ( Pasqua et al, 2010 ; Wang et al, 2015 ; Fei et al, 2018a ; Guo L. et al, 2020 ). Chen et al (2017) reported that the reduction of bacterial protein was associated with the increase of membrane permeability and obstruction in protein expression and synthesis.…”

“…The effects of CBCE on pH in of C. sakazakii ATCC 29544 strains were analyzed based on the method as described by Guo L. et al (2020) . In brief, 1.0 μM carboxyfluorescein diacetate succinimidyl ester dye as the fluorescent probe was added to 10 8 CFU/mL of bacterial suspensions, then incubated at 37°C for 30 min.…”

“…In recent years, a growing number of researchers are focusing their attention on screening natural antibacterial extracts to inhibit food-borne pathogens, because of their safety and nature ( Fei et al, 2018a ; Guo L. et al, 2020 ). Chrysanthemum morifolium is a traditional medicated and edible cash crop and contains polyphenols, flavones, essential oils, and other chemical components, which have been shown to have strong antioxidant, anti-inflammatory, and antibacterial effects ( Kim and Lee, 2005 ; Cui et al, 2014 ; Kuang et al, 2018 ).…”

Screening of Antibacterial Activity, Antioxidant Activity, and Anticancer Activity of Euphorbia hirta Linn. Extracts

“…The antibacterial activity of E. hirta extracts was investigated using the disk diffusion method with some modifications [35][36][37]. The bacterial suspension phase in physiological saline reaches a concentration of McFarland (0.5%) (equivalent to 10 8 CFU/mL).…”