Aging Affects Oral Microflora in Japanese Elderly

Objectives: Aspiration pneumonia is a common cause of death in the elderly, with risk of infection increasing with age. Oral care has been reported to prevent aspiration pneumonia, suggesting that the oral microflora is involved in the onset of this disease. The purpose of this study was to clarify the effect of aging on the oral microflora.

Methods: Forty-eight edentulous volunteers (23 men, 25 women, mean age 71 ± 8 years) were enrolled in the study and instructed to spit out any saliva accumulated over a 5-minute period to measure salivary flow rate and determine number of bacteria in saliva. Bacterial number on the tongue surface was determined using samples obtained by swabbing of anterior section of terminal sulcus along median groove of tongue. Samples were serially diluted and inoculated onto a blood agar plate, incubated at 37°C for 1 week under anaerobic conditions, and number of colony-forming units determined. The Spearman rank correlation coefficient was used to analyze relationships among age, salivary flow rate, and number of bacteria in saliva or on tongue surface.

Results: A positive correlation was confirmed between age and number of bacteria in saliva (r=0.514, p=0.001), and a negative correlation was found between age and total salivary flow rate (r=-0.470, p=0.001). A negative correlation was also confirmed between total salivary flow rate and number of bacteria in saliva (r=-0.598, p=0.002). No correlation, however, was seen between age and number of bacteria on tongue surface (p=0.145).

Conclusion: The results suggest that the density of bacteria in saliva increases with age. Other factors, however, appear to affect number of bacteria on the tongue surface.