Assessing the Effect of Smokeless Tobacco Consumption on Oral Microbiome in Healthy and Oral Cancer Patients

Abstract

Oral cancer is a globally widespread cancer that features among the three most prevalent cancers in India. The risk of oral cancer is elevated by factors such as tobacco consumption, betel-quid chewing, excessive alcohol consumption, unhygienic oral condition, sustained viral infections, and also due to dysbiosis in microbiome composition of the oral cavity. Here, we performed an oral microbiome study of healthy and oral cancer patients to decipher the microbial dysbiosis due to the consumption of smokeless-tobacco-based products and also revealed the tobacco-associated microbiome. The analysis of 196 oral microbiome samples from three different oral sites of 32 healthy and 34 oral squamous cell carcinoma (OSCC) patients indicated health status, site of sampling, and smokeless tobacco consumption as significant covariates associated with oral microbiome composition. Significant similarity in oral microbiome composition of smokeless-tobacco-consuming healthy samples and OSCC samples inferred the possible role of smokeless tobacco consumption in increasing inflammation-associated species in oral microbiome. Significantly higher abundance of Streptococcus was found to adequately discriminate smokeless-tobacco-non-consuming healthy samples from smokeless-tobacco-consuming healthy samples and contralateral healthy site of OSCC samples from the tumor site of OSCC samples. Comparative analysis of oral microbiome from another OSCC cohort also confirmed Streptococcus as a potential marker for healthy oral microbiome. Gram-negative microbial genera such as Prevotella, Capnocytophaga, and Fusobacterium were found to be differentially abundant in OSCC-associated microbiomes and can be considered as potential microbiome marker genera for oral cancer. Association with lipopolysaccharide (LPS) biosynthesis pathway further confirms the differential abundance of Gram-negative marker genera in OSCC microbiomes.

Microbiota and Oral Cancer as A Complex and Dynamic Microenvironment: A Narrative Review from Etiology to Prognosis

“…A lower abundance of Streptococcus genera was observed in patients with OSCC, associated with an oral health condition. There were significantly higher abundance of Streptococcus infantis in smokeless tobacco non-consumers compared to that in smokeless tobacco consumers and contralateral buccal site of OSCC samples compared to that in the OSCC tumor site [ 68 ]. Streptococcus sanguinis , associated with periodontal health [ 69 ], could reduce the colonization of soft tissue surfaces by A. actinomycetemcomitans [ 70 ].…”

Oral Microbiome in Nonsmoker Patients with Oral Cavity Squamous Cell Carcinoma, Defined by Metagenomic Shotgun Sequencing

“…In the previous seven 16S rRNA gene-based studies of microbiome in OC-SCC [ 10 , 11 , 12 , 13 , 14 , 15 , 16 ], six studies included both smokers and nonsmokers in the OC-SCC group [ 10 , 11 , 12 , 13 , 15 , 16 ] and one study excluded current smokers from both cases and controls [ 14 ]. The most striking overrepresentation of genus in controls is Streptococcus in six of the seven studies (6/7) [ 10 , 11 , 12 , 14 , 15 , 16 ], followed by Actinomyces (3/7) [ 11 , 15 , 16 ], Rothia (3/7) [ 10 , 11 , 16 ], Veillonella (3/7) [ 10 , 13 , 16 ], and Haemophilus (2/7) [ 13 , 15 ].…”

“…In the previous seven 16S rRNA gene-based studies of microbiome in OC-SCC [ 10 , 11 , 12 , 13 , 14 , 15 , 16 ], six studies included both smokers and nonsmokers in the OC-SCC group [ 10 , 11 , 12 , 13 , 15 , 16 ] and one study excluded current smokers from both cases and controls [ 14 ]. The most striking overrepresentation of genus in controls is Streptococcus in six of the seven studies (6/7) [ 10 , 11 , 12 , 14 , 15 , 16 ], followed by Actinomyces (3/7) [ 11 , 15 , 16 ], Rothia (3/7) [ 10 , 11 , 16 ], Veillonella (3/7) [ 10 , 13 , 16 ], and Haemophilus (2/7) [ 13 , 15 ]. In contrast, the most striking overrepresentation of genera in OC-SCC are Campylobacter [ 10 , 11 , 12 , 13 , 16 ] and Fusobacterium [ 10 , 12 , 14 , 15 , 16 ] in five of the seven studies (5/7), followed by Peptostreptococcus (4/7) [ 11 , 12 , 13 , 16 ], Catonella (3/7) [ 11 , 13 , ...…”

“…The 16S rRNA gene sequencing method is the most commonly used technique in microbiome-disease association studies due to its cost-effectiveness and the availability of similar studies for comparisons. To date, there have been seven published studies on the microbiome in oral cavity squamous cell carcinoma (OC-SCC) [ 10 , 11 , 12 , 13 , 14 , 15 , 16 ]. Of the 33 genera reported to have an association with OC-SCC, 17 are one-time discoveries not confirmed by other studies and three are controversial associations.…”

“…Several programs are available to predict functional profiles of microbial communities using 16S rRNA gene surveys and known full genomes [ 21 , 22 ]. In the seven microbiome studies in OC-SCC [ 10 , 11 , 12 , 13 , 14 , 15 , 16 ], only three pathways are predicted to be associated with OC-SCC by more than one study [ 10 , 13 , 14 , 15 ], two pathways are predicted with controversial associations [ 12 , 14 , 16 ], while the majority of pathways are one-time discoveries not confirmed by any other study. The low level of agreement between studies may be caused by differences in the 16S rRNA gene survey and reference bacterial genomes used in the prediction, as well as the databases used in pathway classification.…”