A recent study completed 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, meanwhile, was that breast milk also contains bacteria resistant to antibiotics and that 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.

Bacteria Resistant To Antibiotics Found In Breast Milk

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 focused on the bacterial DNA and genes in the milk. They created the most extensive DNA sequence library of breast milk thus far.

The specific focus of the study was the number of antibiotic resistance genes (ARGs). 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 in 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 likely 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.

Antibiotic Use By Mother Impacts The Child

Women can be prescribed an intravenous antibiotic treatment during labour for various reasons, for example if they have tested positive for Streptococcus, a bacterium hazardous to infants. In such cases, antibiotic treatment is intended to prevent the transmission of bacteria living in the birth canal to the infant during delivery. Antibiotic treatment can also be used if the mother's waters have broken long before labour begins, or if potential infection is otherwise suspected.

However, the study indicated that the antibiotic treatment of the mother increases the number of bacteria resistant to antibiotics in the infant's gut. While the study did not demonstrate why this happens, according to one theory, the bacteria that first reach the infant gut gain a head start. Since antibiotics administered to the mother eliminate all bacteria except those resistant to the drug, in such deliveries the mother is likely to pass mainly resistant bacteria on to her child.

However, antibiotic treatment administered during delivery is only one of all the antibiotic courses taken by mothers at some point in their life that may impact the gut microbiota of infants.

The bacterial flora in our gut changes every time we take antibiotics. Antibiotics kill both good and bad bacteria, leaving alive only those bacteria that are resistant to the antibiotic in question. These bacteria may gain a permanent foothold in the gut, even though most of the other bacteria will return soon after the antibiotic treatment as well.

Since the mother transmits bacteria resistant to antibiotics to the infant, all of the antibiotic courses taken by the mother in her life may also affect the bacterial flora of the infant's gut and the prevalence of resistant bacteria in the gut.

One Of The Major Global Health Threats

Bacteria resistant to antibiotics is among the greatest global threats to human health. According to estimates by previous research, bacteria and other micro-organisms resistant to antibiotics and other drugs will, by 2050, cause more deaths than cancer, since infections can no longer be effectively treated.

Bacteria resistant to antibiotics are everywhere. They are present in the human gut, regardless of whether a person has taken antibiotics. They are transmitted between individuals in the same way as bacteria, viruses and other micro-organisms usually are: through, for example, direct contact and in food.

All resistant bacteria do not cause diseases and, thus, do not as such harm their carriers. In suitable conditions, however, such bacteria can either induce the onset of a disease or transfer the gene that provides antibiotic resistance to another bacterial pathogen.

Because such bacteria cannot be killed with antibiotics, and because the immune system of infants is weak, infections caused by resistant bacteria can be fatal to infants. In Finland, where Pärnänen is based, babies die of such infections only rarely. Yet prior studies show that, globally, more than 200,000 newborns die annually of infections, caused by antibiotic-resistant bacteria, that have advanced to the stage of sepsis.