IDSA 2011: New Insights into the Human Microbiome, Part II

The second presenter in the press conference on the human microbiome at the annual meeting of the Infectious Diseases Society of America annual meeting was Samit Joshi, MD, a clinical fellow at the Yale University School of Medicine. (Click here the read the first part of this article.)

Can the Microbiome Predict Pneumonia?

Given that health care associated pneumonia (HCAP) is a growing public health problem and strategies are needed to identify those at high risk of it, Joshi and his colleagues set out to determine whether there was an association between the oral microbial profile and subsequent development of pneumonia. They used gene pyrosequencing to compare oral microbial profiles of healthy adults in the community with those at risk of HCAP—nursing home residents and ICU patients on mechanical ventilators.

The study followed 37 subjects prospectively for a month for pneumonia development. Streptococcaceae were the dominant microbacterial taxa in the mouth, but the average portion taken up by it differed among the three groups: community dwellers (0.65), nursing home residents (0.43), and mechanically ventilated ICU patients (0.33). In addition, ICU patients who went on to develop pneumonia had a significantly lower average portion of oral Streptococcaceae (0.07) than ICU patients who did not develop pneumonia (0.49).

The results suggest that pyrosequencing of oral microbiota could help identify patients at heightened risk of developing HCAP. They also suggest that it might be possible to prevent HCAP by altering the levels of certain bacteria in the oral microbiome.

Relman noted that this was a very exciting development, showing that our microbial communities may be markers of our own physiology and where it is headed. However, he noted that it is not clear whether there is a causal relationship between bacteria levels and health or merely an association between the two. In response to a questioner who asked how one would prove that the shift in oral bacteria is a cause of heightened HCAP risk rather than merely associated with it, Joshi acknowledged that it is difficult to establish causation in humans.

To read the final section of this article, click here.