Salivary bacterial shifts in oral leukoplakia resemble the dysbiotic oral cancer bacteriome

Abstract

Objective : While some oral carcinomas appear to arise de novo , others develop within long-standing conditions of the oral cavity that have malignant potential, now known as oral potentially malignant disorders (OPMDs). The oral bacteriome associated with OPMD has been studied to a lesser extent than that associated with oral cancer. To characterize the association in detail we compared the bacteriome in whole mouth fluid (WMF) in patients with oral leukoplakia, oral cancer and healthy controls. Methods : WMF bacteriome from 20 leukoplakia patients, 31 patients with oral cancer and 23 healthy controls were profiled using the Illumina MiSeq platform. Sequencing reads were processed using DADA2, and taxonomical classification was performed using the phylogenetic placement method. Sparse Partial Least Squares Regression Discriminant Analysis model was used to identify bacterial taxa that best discriminate the studied groups. Results : We found considerable overlap between the WMF bacteriome of leukoplakia and oral cancer while a clearer separation between healthy controls and the former two disorders was observed. Specifically, the separation was attributed to 14 taxa belonging to the genera Megaspheara, unclassified enterobacteria, Prevotella, Porphyromonas, Rothia and Salmonella, Streptococcus, and Fusobacterium . The most discriminative bacterial genera between leukoplakia and oral cancer were Megasphaera, unclassified Enterobacteriae, Salmonella and Prevotella. Conclusion : Oral bacteria may play a role in the early stages of oral carcinogenesis as a dysbiotic bacteriome is associated with oral leukoplakia and this resembles that of oral cancer more than healthy controls. Our findings may have implications for developing oral cancer prevention strategies targeting early microbial drivers of oral carcinogenesis.

Association of Microbiome with Oral Squamous Cell Carcinoma: A Systematic Review of the Metagenomic Studies

“…The surface samples may depict colonizing microbiome, whereas deeper tissue samples might reflect more significant microbiota that may play a potential role. Salivary samples may be reflective of the total oral environment, whereas direct sampling from tissue samples may be more representative of an endogenous microbiome co-evolving with the host [ 42 ]. The microbial communities collected from the mucosal surface by an oral swab may not reflect the tumor-associated microbiome [ 43 , 44 ].…”

Leukoplakia in the Oral Cavity and Oral Microbiota: A Comprehensive Review

“…Similarly, Decsi et al found 43 different species in OPMD compared to 18 species in the healthy mucosa, with only 8 shared by both tissues [11]. These results question the validity of whole-mouth sampling in oral leukoplakia since it may be altered by periodontal disease or dental caries [12].…”

“…Nonetheless, other saliva-based studies were able to identify significant differences in the microbiome composition between OLK and healthy controls [12,[15][16][17][18]. Moreover, although through a highly biased study (i.e., time lag between OLK and sampling; lack of histologic assessment of OLK), Shridhar et al showed a better proportion of quantifiable pathogens from salivary rinse rather than gingival swabs for three selected species [18].…”

“…Every portion of the oral cavity is inhabited by plenty of microorganisms, with differences related to the structure (keratinized vs. non-keratinized) and state of the mucosa [10]. DNA may be extracted by either tissue biopsies [11] or unstimulated saliva, called whole mouth fluid (WMF) [12], or mouth rinse or mucosal swabs. The latter may be taken solely from the OLK or, conversely, from all different oral subsites [13,14].…”

“…Fusobacterium and Veillonella were more abundant in patients with premalignant lesions than in the controls. As far as biodiversity is concerned, only a few studies have investigated alfa-diversity, and they detected either a high bacterial richness [7], depletion [11,15] or even equivalence [12,16] between the OLKs and healthy controls. Instead, beta-diversity has been commonly reported between the same two groups [7,8,12,15], although in some cases the results were difficult to interpret because of different subsite [14] or subgroup analyses [13].…”