How tobacco reshapes the mouth: Studying the oral microbiome in smokers and non-smokers

By Dr. Sanchari Sinha Dutta, Ph.D.Reviewed by Benedette Cuffari, M.Sc.May 8 2024

A recent study published in Scientific Reports compares differences between the composition and diversity of the oral microbiome in cigarette users, smokeless tobacco users, and non-users.

Study: Oral microbiome dysbiosis among cigarette smokers and smokeless tobacco users compared to non-users. Image Credit: fongbeerrredhot / Shutterstock.com

What is the oral microbiome?

The oral microbiome comprises over 700 bacterial species that reside within the oral cavity. These bacterial species require a stable environment to survive, which is dependent on a normal body temperature of 37 °C and optimal nutrition.

Depending on different surface adhesins and oral receptors, specific bacteria preferentially colonize different oral surfaces. Hard oral surfaces can include the teeth, palates, and gingival sulcus, whereas soft tissues include the tongue and cheeks.

Chemical constituents present in tobacco have been shown to significantly influence the composition of the oral microbiome, thereby increasing the risk of oral dysbiosis, which reflects both a loss of beneficial bacteria and an increased concentration of pathogenic bacteria. For example, previous studies have shown that smokeless tobacco products can deplete Lactobacillus and Haemophilus concentrations within the oral cavity. In contrast, cigarette smoking has been shown to reduce the diversity of Gram-positive bacteria within the oral cavity in a time-dependent manner.

Study design

The study cohort comprised 85 individuals, 24 of whom were cigarette smokers, 18 smokeless tobacco users, and 43 non-users. Buccal swabs and saliva samples were collected from the participants over four months at four different time points. DNA extracted from these samples was sequenced to determine the oral microbiome composition and diversity.  

Important observations

No significant temporal differences in alpha and beta bacterial diversity were observed between the study groups at any time point. Similarly, no significant differences in the dominant six bacterial species were observed between the study groups throughout the four-month study period.

Across all study groups, buccal swabs exhibited significantly lower alpha diversity than saliva samples. In both buccal swabs and saliva samples, the lowest alpha diversity was observed in non-users compared to cigarette and smokeless tobacco users.

Firmicutes, Bacteroidetes, Actinobacteria, Proteobacteria, and Fusobacteria were the most abundant bacterial communities present in all samples. Among these species, non-users exhibited the lowest abundance of Firmicutes and the highest abundance of Proteobacteria as compared to cigarette smokers and smokeless tobacco users. The abundance of Bacteroidetes, Actinobacteria, and Fusobacteria was similar between the study groups.

Among the most abundant bacterial genera identified in buccal swabs, a higher abundance of Actinomyces, Granulicatella, Haemophilus, Neisseria, Oribacterium, Prevotella, Pseudomonas, Rothia, and Veillonella was observed in non-users as compared to tobacco users. Among tobacco users, a significantly lower abundance of Leptotrichia and a higher abundance of Pseudomonas was observed in smokeless tobacco users as compared to cigarette smokers. 

Regarding differentially abundant bacterial genera in buccal swabs, non-users exhibited a significantly higher abundance of three Gram-positive and two Gram-negative bacteria as compared to cigarette smokers. Gram-positive bacteria included Streptococcus anginosus, Actinomyces, and Abiotrophia, whereas the two Gram-negative bacteria included Aggregatibacter and Leptotrichiaceae.

Cigarette smokers had a significantly higher abundance of six Gram-positive and 13 Gram-negative bacteria than non-users. Although five Gram-negative and 12 Gram-positive bacteria were significantly more abundant in non-users than smokeless tobacco users, only Coprococcus, a Gram-positive bacterium, exhibited higher abundance in smokeless tobacco users than non-users.  

In saliva samples, 18 Gram-negative and 26 Gram-positive bacteria were significantly more abundant in cigarette smokers than in non-users. In contrast, 31 Gram-negative and 19 Gram-positive bacteria exhibited higher abundance in non-users than in cigarette smokers.

Among non-users and smokeless tobacco users, two Gram-positive and three Gram-negative bacteria showed significantly higher abundance in smokeless tobacco users.

Study significance

Significant changes in oral microbiome composition were observed in cigarette smokers and smokeless tobacco users. Although much of the oral microbiome composition remained relatively stable over time in tobacco users, the relative abundance of certain oral bacteria changed significantly over the study period.

The researchers also identified several opportunistic bacteria in tobacco users, including Neisseria subflava, Bulleidia moorei, and Porphyromonas endodontalis.

Dysbiosis of oral bacterial communities is related to the specific type of tobacco product used.”

Given the potential link between oral microbiome alteration and the development of various oral and non-oral diseases, the study findings indicate that long-term tobacco use may increase the risk of malignancies and other serious health complications.