The UN recently warned that antibiotic resistance will be the leading cause of death in the world by 2050. As the number of bacteria resistant to antibiotics continues to grow, infections will no longer be effectively treated.

Some estimates suggest that 200,000 newborns die worldwide every year of infections caused by antibiotic resistant bacteria. In fact, the number of bacteria resistant to antibiotics in the infant’s gut is ‘worrying’, according to microbiologist Katariina Pärnänen, of the Faculty of Agriculture and Forestry at the University of Helsinki (Finland), and leave infants vulnerable to diseases. “Babies are more likely to suffer from this than adults, even if the babies have never been given antibiotics”, said Pärnänen.

But, how -if babies have not taken antibiotics in their short life- those resistant bacteria end up in their guts? Previous studies had already found small babies had a high abundance of resistant bacteria, compared to adults, who supposedly had had on average several courses of antibiotics in life.

The study also found that infants breastfed for at least six months have fewer antibiotic-resistant bacteria in their guts compared with babies breastfed for a shorter time

In order to throw light to this key question about the origin of those bacteria resistant to antibiotics, Pärnänem and her team engaged 16 mother-infant pairs and, over an 8-month period, studied both subjects’ faeces and the mother’s breast milk, focusing on the bacterial DNA.

The team’s study, published in Nature Communications, not only found that those resistant bacteria came from mothers, during delivery, either if the birth was vaginal or a C-section, but also during breastfeeding. Indeed, the presence of resistance genes is observed in breast milk.

Often,  antibiotics given to the mother during labour to prevent or treat infections, increase the number of antibiotic-resistant bacteria in infants. The Finnish researchers hypothesize that since the antibiotics administered to the mother eliminate potentially dangerous bacteria, such as Streptococcus, except the ones resistant to the drug, the latter are therefore the ones passed on to a baby during birth. That’s why they suggest maybe “physicians could use their findings to consider whether [preventative] practices should be changed or not.”

Although this may seem counterintuitive, the study also found that infants breastfed for at least six months have fewer antibiotic resistant bacteria in their guts compared with babies breastfed for a shorter time.

Breastfeeding is all in all healthy and good for the babies, that’s why the World Health Organisation recommends exclusive breastfeeding for the first six months of life and continue breastfeeding at least until 2 years of age. And now, in addition to all the benefits it has for the baby’s health, Finnish researchers have discovered it also reduces the number of harmful bacteria resistant to antibiotics.

“The positive effect of breastfeeding was also identifiable in infants who were given formula in addition to breast milk,” stated Pärnänen

Researchers think this is due to fermentable sugars present in the milk -called prebiotics– that promote the growth of gut bacteria, like those having probiotic features such as Bifidobacteria.

These beneficial bacteria also prevent the proliferation of other detrimental bacteria. Like in a jungle, where animals and plants compete one species against the others to make theirs the place and gain access to resources, in the gut bacteria, mostly, and other microorganisms also compete to thrive.

“The positive effect of breastfeeding was identifiable also in infants who were given formula in addition to breast milk. Partial breastfeeding already seemed to reduce the quantity of bacteria resistant to antibiotics”, stated Pärnänem.

According to these results, breastfeeding and partial breastfeeding complemented with formula remain a good alternative to keep at a bay the number of resistant genes in the babies gut and try, also, to cut down the global problem of antibiotic resistance.



Pärnänen K, Karkman A, Hultman J, et al. Maternal gut and breast milk microbiota affect infant gut antibiotic resistome and mobile genetic elements. Nat Commun. 2018; 9(1):3891. doi: 10.1038/s41467-018-06393-w.