Lactobacillus paracasei N1115 (Lp N1115) was isolated from fermented milk products. The administration of Lp N1115 is safe and well tolerated in Chinese children, but its effectiveness among young Chinese children is still unclear. To investigate the efficacy of Lp N1115 as a probiotic to enhance gut development in Chinese infants and toddlers born by cesarean section, 109 healthy and cesarean-delivered infants aged 6–24 months were recruited for a 12-week randomized, placebo-controlled trial, with 101 finally completing the study. Saliva and stool samples were collected and detected at weeks 0, 4, 8, and 12 of the intervention. Statistical analyses were performed by using a per-protocol (PP) approach. After 12 weeks of intervention, the fecal pH in the control group increased (p = 0.003), while the fecal pH in the experimental group did not change. Salivary cortisol decreased from baseline in the experimental group (p = 0.023), while the control group showed little change. In addition, Lp N1115 increased the fecal sIgA content of infants aged 6–12 months (p = 0.044) but had no obvious effect on fecal calprotectin and saliva sIgA. At week 4, the increase in Lactobacillus relative to baseline was higher in the experimental group than in the control group (p = 0.019). Further analysis showed a trend toward a higher detection rate of Lactobacillus in the experimental group than in the control group (p = 0.039). In conclusion, Lp N1115 was able to enhance the content of Lactobacillus and maintain fecal pH levels. Its beneficial effects on gut development were more obvious in 6–12-month-old infants.

Cronobacter sakazakii can cause severe infections in premature infants and neonates through the consumption of contaminated milk-based foods. However, the pathogenesis of sequence type 4 (ST4) C. sakazakii remains to be fully elucidated. In this study, four ST4 C. sakazakii strains were investigated via comparative toxicity, genomic, and transcriptomic analyses to elucidate their pathogenic characteristics and mechanisms. Multilocus sequence typing (MLST) indicated that ST4 C. sakazakii was frequently identified among 36 Cronobacter spp. isolates recovered from milk-based infant and baby foods, and 13 novel STs were also detected. Compared with other ST isolates, ST4 C. sakazakii displayed a higher gut weight to carcass weight ratio (GW/CW), stronger abilities to invade and translocate, and increased secretion of TNF-α, IL-1, and lactate dehydrogenase (LDH) in human brain microvascular endothelial cells (HBMECs) and human U251 glioma cells (U251). Moreover, ST4 C. sakazakii strains with a higher GW/CW ratio significantly disrupted routine blood indices, promoted the secretion of inflammatory factors, and induced severe histopathological changes in the liver, brain, spleen, kidney, and intestine of suckling mice. Although differences in genome composition and known virulence factors were observed among these ST4 C. sakazakii strains with varying pathogenic phenotypes, comparative transcriptomic analyses revealed that the expression of numerous virulence factors and pathways, including ompA, ompW, luxS, rpoS, the Sec secretion system, lipopolysaccharide biosynthesis and assembly, and flagellar assembly, greatly contributed to the high pathogenicity of ST4 C. sakazakii. Our findings suggest that foodborne ST4 C. sakazakii isolates represent a significant potential threat to food safety and public health, particularly for premature and immunocompromised infants.