Gut microbiota diversity of hospitalized older adult patients with and without antibiotic-associated diarrhea

Background The incidence of antibiotic-related diarrhea (AAD) is high in older adults. Aim To examine the gut microbiota changes in older adults who received antibiotics to identify the microbial signatures associated with antibiotic use and AAD. Methods A nested prospective observational cohort study was conducted between December 2019 and June 2021 in patients ≥ 65 years old at Huashan Hospital affiliated with Fudan University. The patients were grouped as antibiotic-treated (HA group) and no antibiotics (HC group); the HA group was subdivided as with vs. without AAD. Fecal samples were collected at admission (i.e., before eventual antibiotics) and after 7 days. Result Thirty-eight and 19 participants were included in the HA and HC groups. There were significant differences in gut microbiota between the HA after antibiotics vs. HC groups, with a higher Firmicutes / Bacteroidetes ratio. Before antibiotics in the HA group, the relative abundances of Akkermansia and Alistipes were lower in the AAD subgroup than the no-AAD subgroup, while the relative abundance of Actinomyces was higher. After antibiotics in the HA group, specific bacterial species were decreased in the AAD subgroup compared with the no-AAD subgroup. Among HA participants without probiotics, the abundance of Akkermansia in the patients without AAD was higher than in the patients with AAD at baseline ( P = 0.007). Conclusion Patients with or without AAD have different gut microbiota compositions before antibiotics. Antibiotics can lead to dysbiosis, with a decrease in beneficial bacteria and an increase in Enterococcus .