A pilot study investigating the impact of cigarette smoking on oral nitrate-reducing bacteria within the oral microbiome

Objective
To evaluate the impact of cigarette smoke on the activity and abundance of oral nitrate reducing bacteria (ONRB) in vivo and in vitro.
Materials and Methods
An observational study comprising of eleven cigarette smokers and thirty-one non-smokers. A saliva and nitrate-rinse sample were collected from each participant to analyse salivary biomarkers and the activity and abundance of ONRB in vivo. Additionally, the effect of cigarette smoke on the nitrate-reducing activity of four Rothia species was investigated in vitro.
Results
The beta diversity of the oral microbiome was significantly different between smokers and non-smokers (P = 0.0063). Neisseria flavescens and Actinomyces oris were significantly higher in the saliva of smokers, however, Neisseria subflava, Neisseria oralis, Kingella denitrificans and Actinomyces georgiae were lower. Salivary nitrite levels were significantly lower in smokers (P = 0.034), along with a trend for decreased salivary pH (P = 0.058) and increased salivary thiocyanate (P = 0.018). In vitro exposure to cigarette smoke decreased the nitrate-reducing activity by Rothia species (P = 0.0046).
Conclusions
Smoking decreased salivary nitrite levels and had a species dependent effect on ONRB abundance in vivo and inhibitory effect on the nitrate-reducing activity of Rothia species in vitro.
Clinical significance
A ‘shift’ in the oral microbiome and inhibitory effect on nitrate reduction in smokers may contribute to an increased risk of oral and cardiovascular disease. Better understanding of this pathway may have the potential for development of interventions to decrease disease risk in this group.