Human milk is highly complex, it's personalised to each mother-baby and it changes over time. Now new research shows just how personalised breastmilk is for preterm babies, and how even short courses of antibiotics can have prolonged effects on the diversity and abundance of microbes in a mother's milk.

“It came as quite a shock to us that even one day of antibiotics was associated with profound changes in the microbiota of breast milk,” said Deborah O’Connor, PhD, professor and chair of nutritional sciences at the University of Toronto.

This new research published in Cell Host & Microbe is based on 490 breast milk samples from 86 mothers of preterm babies.

Researchers found the types of microbes present in the milk is highly individualised and changes over time - depending on pre-pregnancy BMI and mode of birth.

The microbes in the milk changed depending on the mother's exposure to antibiotics (class, timing and duration).

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