“…During in utero development and later in life, there are several direct and indirect factors that affect healthy microbiota colonization and subsequent host-microbiota interactions. These factors include mother's health status (Stokholm et al, 2018), diet (Frei et al, 2012;Barcik et al, 2015), transfer of maternal antibodies and microbial molecules (Gomez de Ag€ uero et al, 2016;Koch et al, 2016), mode of delivery (Bosch et al, 2016), and breastfeeding and early-life environment (day care, siblings [Wolsk et al, 2016], pets at home [Sitarik et al, 2018;Tun et al, 2017], traditional farm-like dust at home [Stein et al, 2016;Kirjavainen et al, 2019], and smoking and antibiotic and other drug usage in pregnancy and early childhood [Mitre et al, 2018;Loewen et al, 2018]).…”