The areca nut is a widely consumed psychoactive substance linked to an elevated risk of oral diseases, including oral cancer. Although it is well-established that areca nut chewing disrupts oral microbiota composition, its impact on microbial functions, specifically the underlying strain-level diversity remains elusive, calling for advanced exploration to uncover hidden dynamics. In this study, we constructed a well-defined cohort of 80 long-lived individuals, comprising habitual areca nut chewers and age-matched non-chewers, to investigate the long-term effects of areca nut exposure on the oral microbiome. Species and function-level profiling revealed significant alterations in microbial community structure, including marked shifts in Streptococcus associated with disruption of the thiamine diphosphate salvage pathway. Strain-resolved analysis further identified extensive single nucleotide variations in Neisseria genes btuD and bacA, which are essential for cobalamin transmembrane transport. Notably, similar strain-level alterations were observed in oral cancer patients, suggesting that areca nut chewing may disturb oral vitamin homeostasis and contribute to disease development. Moreover, the combined exposure to areca nut chewing and smoking was associated with more pronounced functional shifts in the oral microbiome, particularly in metabolic pathways related to sulfur and nitrogen cycling. Together, these findings demonstrate that chronic areca nut use induces profound remodeling of the oral microbiome at both functional and genomic levels, providing novel insights into microbial mechanisms potentially linking lifestyle exposures to oral disease, cancer, and broader impacts on human health.

Antibiotics are effective in treating bacterial infections, but they also disrupt the gut microbiota, thereby causing side effects such as diarrhea, flatulence and indigestion. Probiotics and fecal microbiota transplantation (FMT) have attracted widespread attention due to their ability to restore the balance of the gut microbiota and alleviate various conditions. In this study, the mechanism of action of FMT and the probiotic Lacticaseibacillus paracasei HNU502 in alleviating the side effects of cefotaxime, a common antibiotic, using combination of metagenomics, pathological analysis and gas chromatography. The findings suggested that FMT alleviated antibiotic side effects by restoring the disturbed gut microbiota, while HNU502 worked by reestablishing the balance of the gut microbiota. Both FMT and probiotic supplementation improved gut microbiota composition, but to varying degrees, prevented goblet cell loss, and increased the contents of mucin-2 (MUC-2) and zonula occludens-1 (ZO-1), thus aiding gut mucosal recovery. Moreover, the two approaches ameliorated the metabolic disorders of short-chain fatty acids, inhibited the secretion of pro-inflammatory cytokines such as interleukin (IL)-1β, IL-6 and tumor necrosis factor (TNF)-α as well as blood urea nitrogen (BUN), and effectively reduced virulence factor enrichment. This study contributes to a better understanding of the link between human health and gut microbiota, and provides new therapeutic options for mitigating antibiotic side effects, which is of great significance for improving patients’ health status and quality of life.