The nasal microbiome of infants may impact risk of developing asthma

Many lower respiratory illnesses have been shown to associate with specific lung, throat and nasal bacteria, but the role of the microbiome is still unclear, and mechanisms for the connection have yet to be proven.  Of particular interest is asthma, which affects around 7% of people in the US, and increases a person’s risk for many other conditions.  While it is normally diagnosed in toddlers, scientists believe that the groundwork for the disease is actually laid during infancy.  With that in mind, researchers in Australia performed the first longitudinal study of infants’ nasopharyngeal (nose and throat) during the first year of their lives, and tracked episodes of respiratory illness during that time.  They discovered a strong connection between the microbiome and respiratory illness, including asthma, and last month published their results in Cell Host and Microbe.

The researchers collected nasopharyngeal microbiome samples from 234 infants at different time points during their first year of life.  Most infants’ microbiomes were dominated by the following species: Moraxella catarrhalis, Streptococcus pneumoniae, Staphylococcus aureus, Haemophilus influenzae, and Alloiococcus otitidis.  Interestingly, this was true for infants regardless of birth delivery mode (i.e. cesarean or vaginal) as well as length of breast feeding.  In contrast, having a furry animal in the house tended to increase the abundance of Streptococcus, but having older siblings tended to decrease it.  In addition, there were strong seasonal effects on the microbiome, with Haemophilus being associated with the summer, and Moraxella the winter.  In children with respiratory illness, Haemophilus, Moraxella, and Streptococcus were most frequently measured, and Staphylococcus, Alloiococcus, and Corynebacterium least frequently measured.

When the scientists compared their results with the asthma outcomes of the children at 5 years old they noticed one significant trend.  Colonization by Streptococcus at around 2 months old, which was asymptomatic at the time and occurred in 14% of infants tested, was strongly connected to chronic wheezing (itself an indication of asthma) at 5 years old.  They suggest that the developing airways in infants may be especially vulnerable to Streptococcus.

This long term study does a really nice job of defining how the microbiome grows and develops in the airways of infants – something which previously hadn’t been performed at such a large scale.  While this study alone does not figure out exactly what the microbiome’s role is in childhood respiratory illnesses, it does provide a baseline for future studies to work off of.   

Bacteria in the back of our nose can cause pneumonia

I can tell you from first hand experience, getting pneumonia is not a fun experience. It can actually be quite deadly and results in approximately 1.3 million childhood deaths each year worldwide.  One of the causes of pneumonia is invasive pneumococcal disease, or a fancy way of saying a bacterial infection caused by a specific bacterium, Streptococcus pneumonia (or the pneumococcus). This bacterium often resides in the place where your mouth and nose connect called the nasopharynx. A better understanding of the relationship between this bacteria and the nasal microbiome will allow for a better ability to modulate the bacteria and prevent or treat diseases like pneumonia or meningitis.

Scientists recently published a study in the journal Microbiome that compared the nasopharyngeal microbiome of individuals who were natural carriers of this bacterium and those who were not.  In a study of 40 individuals, 10 were natural carriers of the pneumococcus and 30 were not. Those who were not were inoculated (vaccinated) through their nose with one of two strains of the bacteria.

They found that the natural carriers had greater phylogenetic distances (PD) between the bacteria in their nasopharyngeal microbiome. Phylogenetic distance is a measure of how common the ancestors of specific bacteria are. Those with a greater PD had bacteria that had common ancestors a longer time ago than those with a lower PD.  In individuals who were not carriers and were inoculated with the bacterial strains, those who had a more diverse microbiome resulted in pneumococcal carriage being established, meaning the presence of S. pneumonia, was identified in the nasopharynx.

This study provided a model for studying the interaction between the microbiome of our nose and specific bacteria that are important for disease onset. We often see that in an environment like the gut with a more diverse microbiome, bacteria are unable to colonize and establish a presence, but the opposite is true in this case. Those with a more diverse microbiome often had pneumococcus in their nose after inoculation.  It is proposed that carriage of pneumococcus results in an immunizing event and therefore the ability for the bacteria to become established is beneficial and helps establish better immunity.  Better understanding of this relationship will be important for better immunizations and preventing invasive pneumococcal disease.