BOSTON – In addition to causing cavities, oral microbes may be linked to the risk for health care–associated pneumonia, a small study has shown.
In the study, intubated patients in an ICU were found to have oral microbial profiles that were significantly different from those of similar patients who did not develop pneumonia, reported Dr. Samit Joshi of the section of infectious diseases at Yale University in New Haven, Conn.
The study investigators also found that mouth-dwelling microbe profiles of community-dwelling healthy adults differed markedly from those of adults at higher risk for pneumonia, including nursing home residents and patients on mechanical ventilation.
"We showed that as the risk for pneumonia increased among these three groups of adults, that certain types of bacteria living in their mouths decreased. Interestingly, in the adults who actually developed pneumonia, other disease-causing bacteria in their mouths actually increased days before those adults developed pneumonia," Dr. Joshi said in a briefing.
The findings suggest that genetic sequencing of oral microbial communities in patients’ mouths may provide novel methods for targeted prevention of pneumonia, he added.
The investigators took swab samples from the mouths of 19 healthy, community-dwelling adults (mean age, 60.1 years); 10 nursing home residents (86.2 years); and 8 patients in an ICU (51.6 years). The nursing home residents had been living in the facility for a mean of 33.2 months; the ICU patients had been in the unit for a mean of 3.6 days.
Samples of bacteria collected from the palate, buccal mucosa, tongue, and gingival crevice were then analyzed with165 ribosomal RNA pyrosequencing, a sophisticated technology suitable for complex microbiome analyses, but not available for bedside or point of care assays.
"We showed that as the risk for pneumonia increased among these three groups of adults, that certain types of bacteria living in their mouths decreased."
The authors found that bugs in the family Streptococcaceae were the dominant oral residents, but in proportions that differed significantly among the three patient groups: 65% among community dwellers, 43% among nursing home residents, and 33% among the ICU patients, all of whom were on mechanical ventilation.
Three of the patients went on to develop pneumonia at around 1 week of their ICU stay, and these patients had significantly smaller average proportions of oral Steptococcaceae species than did ICU patients who did not develop pneumonia (0.07% vs. 49%).
The authors then looked at the mean weighted UniFrac distance, which allows for phylogenetic comparisons of microbial communities, and found a significant difference between ICU residents who developed pneumonia and those who were spared from it.
"This discovery has implications for how we prevent pneumonia in the future," Dr. Joshi said at the annual meeting of the Infectious Diseases Society of America. "It may lead to new and improved ways that we can prevent pneumonia by maintaining the composition of bacteria which live inside our mouths, or by maintaining our local immune defense mechanisms."
The idea that microbial communities may be markers of disease is "exciting," said Dr. David Relman, professor of medicine at Stanford (Calif.) University. "What we don’t know right now is whether the two are linked causally – these changes in the microbial composition and the onset of disease – but regardless, I think there is value in understanding these novel kinds of markers of pneumococcal disease," he commented. Dr. Relman was not involved in the study, but moderated a briefing where the data were presented.
The study was funded by the National Institute on Aging and the Howard Hughes Medical Institute. Dr. Joshi and Dr. Relman each reported that they had no relevant financial disclosures.