Tea polyphenols inactivate Cronobacter sakazakii isolated from powdered infant formula.

This study evaluated the antimicrobial activity of tea polyphenols (TP) against 4 Cronobacter sakazakii strains with different sequence types (ST) isolated from powdered infant formula (PIF). The results showed that in normal saline, 5mg/mL of TP (pH 3.44) could eliminate approximately 7.0 log cfu/mL of C. sakazakii within 1 h; in rehydrated PIF, after acidification with HCl (pH 3.55), TP showed a stronger antibacterial activity compared with the controls (malic acid, ascorbic acid, and citric acid). Further, some differences were obvious in tolerance to TP between C. sakazakii strains with different ST. The tolerance of C. sakazakii CE1 (ST4) to TP was found to be greater than that of the other 3 C. sakazakii strains (ST1, ST8, and ST64). The results of recovered test and transmission electron microscope analysis revealed that the action of TP against C. sakazakii was an irreversible bactericidal process caused by leakage of cytoplasm. Taken together, these results indicated that TP had an effective bactericidal effect against C. sakazakii, and provided a new idea for preventing and inactivating C. sakazakii in PIF.

Evaluation of improved γ-aminobutyric acid production in yogurt using Lactobacillus plantarum NDC75017.

Most γ-aminobutyric acid (GABA)-producing microorganisms are lactic acid bacteria (LAB), but the yield of GABA is limited in most of these GABA-producing strains. In this study, the production of GABA was carried out by using Lactobacillus plantarum NDC75017, a strain screened from traditional fermented dairy products in China. Concentrations of substrate (l-monosodium glutamate, L-MSG) and coenzyme (pyridoxal-5-phosphate, PLP) of glutamate decarboxylase (GAD) and culture temperature were investigated to evaluate their effects on GABA yield of Lb. plantarum NDC75017. The results indicated that GABA production was related to GAD activity and biomass of Lb. plantarum NDC75017. Response surface methodology was used to optimize conditions of GABA production. The optimal factors for GABA production were L-MSG at 80 mM, PLP at 18 µM, and a culture temperature of 36 °C. Under these conditions, production of GABA was maximized at 314.56 mg/100 g. Addition of Lb. plantarum NDC75017 to a commercial starter culture led to higher GABA production in fermented yogurt. Flavor and texture of the prepared yogurt and the control yogurt did not differ significantly. Thus, Lb. plantarum NDC75017 has good potential for manufacture of GABA-enriched fermented milk products.

Comparison of methods for the microbiological identification and typing of Cronobacter species in infant formula.

Cronobacter species represent an emerging opportunistic foodborne pathogen associated with meningitis and necrotizing enterocolitis in infants. Current evidence indicates that powdered infant formula (PIF) is the main source of Cronobacter contamination. A total of 75 strains of Cronobacter spp. from different geographic regions, as well as from PIF processing environments, were identified and typed with different methods, including biochemical profiling by the API 20E system (bioMérieux, Marcy l'Etoile, France), protein profiling by matrix-assisted laser desorption/ionization time-of-flight mass spectrometry (MALDI-TOF MS), and genotypic profiling by ribotype. Analysis by MALDI-TOF MS and biochemical identification was more accurate compared with ribotype analysis. However, MALDI-TOF MS typing and ribotype analysis showed more discriminatory ability compared with biochemical phenotyping. In conclusion, MALDI-TOF MS is a rapid and reliable tool to identify Cronobacter spp. in PIF and has the potential to trace dissemination of Chronobacter along the production chain.