Antibacterial Activity of Taraxacum officinale against Foodborne Pathogens
Antibacterial Activity of Taraxacum officinale against Foodborne Pathogens
Jiang Wu*
ABSTRACT
This study was aimed to investigate antibacterial activity of chemical constituents of Taraxacum officinale against foodborne pathogens. A total of 133 retail meat products were randomly purchased from different supermarkets. All samples were isolated and identified by conventional methods as Staphylococcus aureus, Salmonella, Escherichia coli and Listeria monocytogenes. Different bacteria were respectively inoculated into LB medium, the OD600 was adjusted to 0.5, and the initial bacterial concentration was adjusted to about 5×108 CFU/mL. T. officinale were dried in a hot air oven, and chemical substances in the dried powder were separated using Soxhlet extraction method with light petroleum as organic solvent. The antibacterial properties of T. officinale extracts against foodborne pathogens were evaluated by agar diffusion method. Sub-inhibitory concentration (SIC) value, minimum inhibitory concentration (MIC) value and minimum bactericidal concentration (MBC) value were measured. The virulence gene expression of the four foodborne pathogens was analyzed by quantitative real-time PCR (qRT-PCR). A microplate reader was used to monitor cell growth at 600 nm with 1 h interval. Environmental scanning electron microscope (ESEM) was used to analyze morphological changes of E. coli and Staph. aureus cells. ATP analysis kit and EnSpire microplate reader were used to detect the intracellular ATP concentration of 4 foodborne pathogens. According to our results of all the tested samples, 38 (28.57%) were found to have Staph. aureus, 27 (20.30%) had Salmonella, 46 (34.59%) had E. coli, and 22 (16.54%) had L. monocytogenes. Staph. aureus had MIC of 0.55±0.18μg/ml and MBC of 1.13±0.11μg/ml; Salmonella had MIC of 0.25±0.13μg/ml and MBC of 0.54±0.06μg/ml; E. coli had MIC of 1.07±0.15μg/ ml and MBC of 2.08±0.19μg/ml; L. monocytogenes had MIC of 0.56±0.11μg/ml and MBC of 1.05±0.13μg/ml. After treatment, reduced expression was shown in Staph. aureus isolates’ seb, hlg and icaA virulence genes, Salmonella isolates’ mogA, ssel, mgtC, siiE and sopB virulence genes, E. coli isolates’ astA, estlb, pic, escV and aggR virulence genes and L. monocytogenes isolates’ LLO, plcA, plcB, actA and inlA virulence genes (P<0.05). The growth rate of E. coli and Staph. aureus strains decreased at 1/2 MIC. When the chemical constituent concentration in T. officinale increased to MIC, the bacteria growth was completely inhibited. Untreated E. coli and Staph. aureus displayed typical bacilli-like and spherical morphology with uniform cell size, and the cell surface looked intact and shiny. On the contrary, when the cells were treated with increased concentration of chemical constituents of T. officinale, the cells exhibited irregular morphology, aggregated and showed extensive surface collapse, thereby increasing the rate and extent of cell damage. After treatment, in the presence of chemical constituents of T. officinale, the intracellular ATP concentration was significantly reduced in the treated Staph. aureus, Salmonella, E. coli and L. monocytogenes (P<0.05). When the chemical constituent concentration of T. officinale plant increased from 1/2 MIC to MIC, the intracellular ATP content further decreased (P<0.05). We concluded that the chemical constituents of T. officinale have antibacterial activity against the two Gram-positive and two Gram-negative bacteria. The chemical constituents of T. officinale can inhibit the growth of foodborne pathogens by inhibiting the expression of virulence genes and reducing permeability of cell membranes, thereby changing the cell morphology and reducing intracellular ATP concentration.
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October 2022
Vol. 54, Iss. 5, Pages 2003-2500
