Age-related changes in production of short chain fatty acids by oropharyngeal microbiota in patients without respiratory tract and oral disorders

Abstract

Rationale: Functional activity of upper respiratory tract and oral microbiota has a high informational potential for diagnostics of infectious disease and for development of preventive measure, which is to be explained by rapid variability and high activity of bacteria in this location. Aim: To determine statistical characteristics of concentrations and ratios of the oropharyngeal short chain fatty acids (SCFA) (i.e., functional activity of oropharyngeal microbiota) depending on age of patients without infectious disorder of upper respiratory tract and oral cavity. Materials and methods: Gas liquid chromatography was used to measure SCFA concentrations in saliva from 683 patients aged from 1 month to 85 years who did not have any infections of respiratory tract and oral cavity. Age intervals with homogenous salivary SCFA levels were determined with constant trends in their means (medians) with one-month accuracy. The resulting parameters for the identified age intervals were compared with Mann-Whitney test at 95% significance level (p < 0.05). Results: There were no significant differences between median total SCFA levels (8.04 [4.85; 14.22] mmol/G) and median acetic acid levels (6.27 [3.79; 11.21] mmol/G) in saliva from patients of all ages from 1 month to 85 years. For all other parameters, from 2 to 3 steps of changes were found that occurred at the age of 4 months and 14 years. After the age of 14, the concentrations of propionic and butyric acid significantly increased, whereas those of valeric and caproic acids, as well as of the branched chain SCFA decreased. Correspondingly, after the age of 14, the mean structural index increased from 0.25 to 0.27 U (p < 0.05). The isoacid index decreased with age in two steps: at the age of 4 months from 1.89 to 1.04 U (p < 0.05) and later at the age of 14 years to 0.74 U (p < 0.05). Conclusion: Salivary SCFA levels become stable at the age of 14. The structural index and the isoacid index are most sensitive to the integral changes in the microbiota composition. Analysis of the results of studies on metabolic functioning of microflora should be based on mathematic modeling and multifactorial statistics in three age intervals: from birth to 4 months of age, from 4 months to 14 years and over 14 years.