Polyphenols are a group of active ingredients in olive oil, and have been reported to exhibit antioxidant activity. Salmonella enterica subsp. enterica serovar Typhimurium (Salmonella Typhimurium) and Staphylococcus aureus are common foodborne pathogens causing serious infections and food poisoning in humans. This study was conducted to analyze the antibacterial activity of olive oil polyphenol extract (OOPE) against Salmonella Typhimurium and S. aureus, and reveal the possible antibacterial mechanism. The antibacterial activity was estimated using minimum inhibitory concentration (MIC) values and bacterial survival rates when treated with OOPE. The antibacterial mechanism was revealed through determinations of changes in intracellular ATP concentration and cell membrane potential, sodium dodecyl sulfate–polyacrylamide gel electrophoresis, and transmission electron microscopy analysis. The results showed the MICs of OOPE against Salmonella Typhimurium and S. aureus were 0.625 and 0.625–1.25 mg/mL, respectively. The growth of Salmonella Typhimurium and S. aureus (∼8 log CFU/mL) was completely inhibited after treatments with 0.625 mg/mL of OOPE for 3 h and 0.625–1.25 mg/mL for 5 h, respectively. When Salmonella Typhimurium and S. aureus were exposed to OOPE, the physiological functions associated with cell activity were destroyed, as manifested by reduction of intracellular ATP concentrations, cell membrane depolarization, lower bacterial protein content, and leakage of cytoplasm. These findings suggested a strong antibacterial effect of OOPE against Salmonella Typhimurium and S. aureus, and provided a possible strategy of controlling contamination by these two pathogens in food products.

This study was conducted to reveal the prevalence, molecular characterization, and antibiotic susceptibility of Bacillus cereus isolated from dairy products including powdered infant formula, raw milk, pasteurized milk, ultra-high-temperature milk, and cheese. Five hundred samples collected from 5 provinces in China were analyzed in overall experiments. Multilocus sequence typing, distribution of toxin genes, and antibiotic susceptibility of the isolates were analyzed. Fifty-four B. cereus strains were detected; of these, 13 isolates (26%) were from raw milk, 12 isolates (12%) from pasteurized milk, 10 isolates (10%) from cheese, 12 isolates (8%) from ultra-high-temperature milk, and 7 isolates (7%) from powdered infant formula. These isolates were divided into 24 sequence types (ST); among them, ST24, ST26, ST82, ST142, ST377, ST857, and ST1046 were the main dominant ST. The results of detection of toxin genes (hblA, hblC, hblD, nheA, nheB, nheC, cytK, entFM, bceT, hlyII, and cesB) showed that 94.4% isolates carried nheABC genes, whereas only 11.1% of the isolates contained the hblACD gene cluster. In addition, detection rates of cytK, bceT, entFM, hlyII, and cesB genes were 75.9, 77.8, 85.2, 53.7, and 11.1%, respectively. The antibiotic susceptibility test indicated that most of B. cereus isolates were resistant to ampicillin, penicillin, cefepime, cephalothin, and oxacillin, and were susceptible to gentamicin, chloramphenicol, imipenem, tetracycline, ciprofloxacin, trimethoprim-sulfamethoxazole, erythromycin, kanamycin, and cefotetan. Therefore, this study revealed the prevalence and characteristics of B. cereus isolated from dairy products in China, indicating the potential risk and contributing to the effective prevention and control of this pathogen.

Olive oil polyphenol extract (OOPE) has been reported to have antibacterial activity; however, its effect on Listeria monocytogenes is less studied so far. This study, thus, aimed to reveal its antimicrobial activity and action approach against L. monocytogenes via evaluating the minimum inhibitory concentration (MIC) as well as the changes of intracellular adenosine 5′-triphosphate (ATP) concentration, cell membrane potential, bacterial protein, DNA, and cell morphology. The results showed that OOPE could inhibit the growth of L. monocytogenes with a measured MIC of 1.25 mg/ml. L. monocytogenes cells treated by OOPE showed significant reduction in intracellular ATP concentrations, bacterial protein, or DNA (p < 0.05), in comparison with those without any treatment. In addition, OOPE was observed to depolarize strain cells and alter cell morphology, resulting in damaged cell membrane and, thereby, leakage of cell fluid. These findings demonstrated that OOPE had inhibition on L. monocytogenes via its action on cells, suggesting its potential as a natural preservative.

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 (pH_in), 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 pH_in, 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.

Cronobacter sakazakii is an opportunistic food-borne pathogen that endangers the health of neonates and infants. This study aims to elucidate the antibacterial activity and mechanism of Chrysanthemum buds crude extract (CBCE) against C. sakazakii and its application as a natural disinfectant. The antibacterial activity was evaluated by the determination of the diameter of inhibition zone (DIZ), minimum inhibitory concentration (MIC), and minimum bactericide concentration (MBC). The antibacterial mechanism was explored based on the changes of growth curve assay, intracellular ATP concentration, membrane potential, intracellular pH (pH_in), content of soluble protein and nucleic acid, and cell morphology. Finally, the inactivation effects of CBCE against C. sakazakii in biofilm on stainless steel tube, tinplate, glass, and polystyrene were evaluated. The results showed that the DIZ, MIC, and MBC of CBCE against C. sakazakii were 14.55 ± 0.44–14.84 ± 0.38 mm, 10 mg/mL, and 20 mg/mL, respectively. In the process of CBCE acting on C. sakazakii, the logarithmic growth phase of the tested bacteria disappeared, and the concentrations of intracellular ATP, pH_in, bacterial protein, and nucleic acid were reduced. Meanwhile, CBCE caused the cell membrane depolarization and leakage of cytoplasm of C. sakazakii. In addition, about 6.5 log CFU/mL of viable C. sakazakii in biofilm on stainless steel tube, tinplate, glass, and polystyrene could be inactivated after treatment with 1 MIC of CBCE for 30 min at 25°C. These findings reveal the antibacterial activity and mechanism of CBCE against C. sakazakii and provide a possibility of using a natural disinfectant to kill C. sakazakii in the production environment, packaging materials, and utensils.