Occurrence, Molecular Characterization, and Antibiotic Resistance of Cronobacter sakazakii in Goat Milk-Based Infant Formula from Shaanxi Province, China.

This study aimed to investigate the prevalence of Cronobacter sakazakii in goat milk-based infant formula (GIF) collected from Shaanxi Province, China, and reveal the molecular characterization and antibiotic resistance profile of these isolates. A total of 750 GIF samples were collected from the retail markets in 5 cities in Shaanxi Province from February 2019 to February 2021. Molecular characterization was investigated using multilocus sequence typing and O-antigen serotyping. Antibiotic resistance of C. sakazakii isolates was assessed using antimicrobial susceptibility testing. Thirty-two strains of C. sakazakii were isolated from GIF samples with a prevalence rate of 4.27% and were divided into 16 sequence types (STs); among them, ST4 (6/32, 18.75%) and ST21 (5/32, 15.63%) were dominant. Five C. sakazakii serotypes (O2, O1, O7, O4, and O3) were detected, and C. sakazakii serotype O2 (15/32, 46.88%) was the main. Of the 21 antimicrobials, isolates showed higher resistance against cephalothin (87.5%), amoxicillin (25%), azithromycin (18.75%), oxytetracycline (18.75%), ampicillin (12.5%), and streptomycin (12.5%). In addition, three isolates were found to be resistant to three antimicrobials. These findings revealed the potential epidemiological risk and characterization of C. sakazakii in GIF from Shaanxi Province, China, and provided reference data for the effective prevention and control of C. sakazakii in powdered infant formula.

Antibacterial Mode of Eucommia ulmoides Male Flower Extract Against Staphylococcus aureus and Its Application as a Natural Preservative in Cooked Beef.

The research was conducted to elucidate the antibacterial performance and mode of action of Eucommia ulmoides male flower extract (EUMFE) against Staphylococcus aureus and its application as a natural preservative in cooked beef. The antibacterial activity was evaluated by determining the diameter of inhibition zone (DIZ), minimum inhibitory concentration (MIC), and minimum bactericide concentration (MBC). The changes in membrane potential, contents of bacterial DNA and protein, integrity and permeability of the cell membrane, and cell morphology were analyzed to reveal the possible mode of action. The effect of EUMFE on the counts of S. aureus, pH, color, total volatile basic nitrogen (TVB-N), and thiobarbituric acid reactive substances (TBARS) of the cooked beef stored at 4°C for 9 days were studied. The results showed that the DIZ, MIC, and MBC of EUMFE against S. aureus were 12.58 ± 0.23 mm, 40 mg/mL, and 80 mg/mL, respectively. The mode of action of EUMFE against S. aureus included hyperpolarization of cell membrane, decrease in bacterial DNA and protein contents, destruction of cell membrane integrity, increase in cell membrane permeability, and damage of cell morphology. After treatments with EUMFE, the growth of S. aureus and lipid oxidation in cooked beef were significantly inhibited (P < 0.05). The pH and TVB-N values of cooked beef treated with EUMFE were significantly reduced as compared to control group (P < 0.05). The color of cooked beef samples containing EUMFE showed decreased L* and b* values, and increased a* and ΔE* values. Therefore, our findings showed that EUMFE had a good antibacterial effect on S. aureus, and provided a theoretical basis for the application of EUMFE as a natural preservative in the preservation of cooked beef.