Inclusion Criteria:  Mothers over 18 years, treated by amoxicillin for at least 2 days who breastfeed their child, - Participation requires that breastfeeding is already well established (i.e., at least 2 weeks after giving birth in order to sample mature milk) and that the infant is over 4 weeks old, Affiliation to the social security scheme or equivalent, Ability to understand and willingness to sign a written Informed Consent document.  Exclusion Criteria:  Mothers under 18 years old, Infants born prematurely (i.e., gestational age under 34 weeks) or requiring appropriate medical supervision or support from a team of social workers, Mothers who gave birth to twins, Inability to communicate due to language problems for the mother, Patient subject to a legal protection order (curatorship or tutorship).