Nitrate-reducing activity, normalized for saliva weight, in swab samples collected from the mouths of preterm (born at <35 wk gestation) and term (born at >36 wk) infants in the neonatal intensive care unit (NICU) or from healthy infants in an outpatient clinic between 2 and 6 wk after birth, or from normal healthy adults. Mammalian cells lack the enzymes required for nitrate reduction, but bacteria dwelling in crypts of the tongue bring about the reaction. Note that the rate in infants is ~10% of that in adults. (Figure adapted from Kanady et al., 2012 (26).)