Breastfed babies less antibiotic-resistant

A new study shows that babies that are breastfed for at least six months have less antibiotic-resistant bacteria in their gut compared to infants who are breastfed for a shorter time.

On the other hand, use of antibiotic by mothers increases the number of antibiotic-resistant bacteria in infants, said a press release of the University of Helsinki.

The study conducted at the University of Helsinki investigated the amount and quality of bacteria resistant to antibiotics in breast milk and the gut of mother-infant pairs, resulting in three findings.

First, infants who were breastfed for at least six months had a smaller number of resistant bacteria in their gut than babies who were breastfed for a shorter period or not at all. In other words, breastfeeding seemed to protect infants from such bacteria.

Second, antibiotic treatment of mothers during delivery increased the amount of antibiotic-resistant bacteria in the infant gut. This effect was still noticeable six months after delivery and the treatment.

The third finding was that breast milk also contains bacteria resistant to antibiotics and the mother is likely to pass these bacteria on to the child through milk. Nevertheless, breastfeeding reduced the number of resistant bacteria in the infant gut, an indication of the benefits of breastfeeding for infants.

Microbiologist Katariina Pärnänen of the University of Helsinki’s Faculty of Agriculture and Forestry investigated with her colleagues the breast milk and faecal matter of 16 mother-infant pairs. The DNA in the milk and faeces was sequenced, or its genetic code was decoded. However, the study did not focus on the mother’s DNA found in milk. Rather, the researchers mapped out the bacterial DNA and genes in the milk. They created the most extensive library of DNA thus far found in breast milk.

“Such studies were impossible only a few years ago. For instance, the laboratory techniques required for processing DNA into sequenceable form have advanced to the extent that the amount of source material needed is today a thousand times smaller than, say, five years ago,” Pärnänen said.

The specific focus of the study was the number of antibiotic resistance genes (ARG). Such genes make bacteria resistant to certain antibiotics, and they are often able to transfer between bacteria. Individual bacteria can have several antibiotic resistance genes, making them resistant to more than one antibiotic.

The study demonstrated for the first time that breast milk indeed contains a significant number of genes that provide antibiotic resistance for bacteria, and that these genes, as well as their host bacteria, are most likely transmitted to infants through the milk. Mothers transmit antibiotic-resistant bacteria residing in their own gut to their progeny in other ways as well, for example through direct contact. Yet, only some of the resistant bacteria found in infants originated in their mothers. The rest were probably originated from the environment and other individuals.

The study does, however, support the notion that breastfeeding overall is beneficial for infants. Although breast milk contains bacteria resistant to antibiotics, sugars in the milk provide sustenance to beneficial infant gut bacteria, such as Bifidobacteria, which are used as probiotics. Breast milk helps such useful bacteria gain ground from resistant pathogens, which is probably why infants who were nursed for at least six months have less antibiotic-resistant bacteria in their gut compared to infants who were nursed for a shorter period.

“As a general rule, it could be said that all breastfeeding is for the better,” said Pärnänen.

She said, “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. Another finding was that nursing should be continued for at least the first six months of a child’s life or even longer. We have already known that breastfeeding is all in all healthy and good for the baby, but we now discovered that it also reduces the number of bacteria resistant to antibiotics.”

The study was carried out in cooperation between the University of Helsinki, the University of Turku, the Turku University Hospital, and the University of Gothenburg.

The study paper published by the journal Nature Communications is titled “Maternal gut and breast milk microbiota affect infant gut antibiotic resistome and mobile genetic elements.”