Characterization of the salivary microbiome in patients with pancreatic cancer.

Pedro J Torres,Kelly S Doran,Michael Bouvet,Sean M Gibbons,Scott T Kelley,Erin M Fletcher

doi:10.7717/peerj.1373

Abstract

Clinical manifestations of pancreatic cancer often do not occur until the cancer has undergone metastasis, resulting in a very low survival rate. In this study, we investigated whether salivary bacterial profiles might provide useful biomarkers for early detection of pancreatic cancer. Using high-throughput sequencing of bacterial small subunit ribosomal RNA (16S rRNA) gene, we characterized the salivary microbiota of patients with pancreatic cancer and compared them to healthy patients and patients with other diseases, including pancreatic disease, non-pancreatic digestive disease/cancer and non-digestive disease/cancer. A total of 146 patients were enrolled at the UCSD Moores Cancer Center where saliva and demographic data were collected from each patient. Of these, we analyzed the salivary microbiome of 108 patients: 8 had been diagnosed with pancreatic cancer, 78 with other diseases and 22 were classified as non-diseased (healthy) controls. Bacterial 16S rRNA sequences were amplified directly from salivary DNA extractions and subjected to high-throughput sequencing (HTS). Several bacterial genera differed in abundance in patients with pancreatic cancer. We found a significantly higher ratio of Leptotrichia to Porphyromonas in the saliva of patients with pancreatic cancer than in the saliva of healthy patients or those with other disease (Kruskal–Wallis Test; P < 0.001). Leptotrichia abundances were confirmed using real-time qPCR with Leptotrichia specific primers. Similar to previous studies, we found lower relative abundances of Neisseria and Aggregatibacter in the saliva of pancreatic cancer patients, though these results were not significant at the P < 0.05 level (K–W Test; P = 0.07 and P = 0.09 respectively). However, the relative abundances of other previously identified bacterial biomarkers, e.g., Streptococcus mitis and Granulicatella adiacens, were not significantly different in the saliva of pancreatic cancer patients. Overall, this study supports the hypothesis that bacteria abundance profiles in saliva are useful biomarkers for pancreatic cancer though much larger patient studies are needed to verify their predictive utility.

Highlights

In the United States, approximately 40,000 people die every year from pancreatic adenocarcinoma, making it the fourth leading cause of cancer related death
Our analysis of salivary microbial profiles supports prior work suggesting that salivary microbial communities of patients diagnosed with pancreatic cancer are distinguishable from salivary microbial communities of healthy patients or patients with other diseases, including non-pancreatic cancers
We observed differences in the mean relative abundances of particular genera in pancreatic cancer patients compared to other patient groups (Fig. 2)

Summary

Introduction

In the United States, approximately 40,000 people die every year from pancreatic adenocarcinoma, making it the fourth leading cause of cancer related death. Recent research has shown that men with periodontal disease have a two-fold greater risk of developing pancreatic cancer after adjusting for smoking, diabetes, and body mass index (Michaud et al, 2007). Researchers have identified a core microbial community in healthy individuals (Zaura, Keijser & Huse, 2009) and shifts from this core microbiome have been associated with dental carries and periodontitis (Berezow & Darveau, 2011). The composition of bacterial communities in saliva seems to reflect health status under certain circumstances (Yamanaka et al, 2012), making the analysis of salivary microbiomes a promising approach for disease diagnostics. A study by Mittal et al (2011) found that increases in the numbers of Streptococcus mutans and lactobacilli in saliva have been associated with oral disease prevalence, while another study showed that high salivary counts of Capnocytophaga gingivalis, Prevotella melaninogenica and Streptococcus mitis may be indicative of oral cancer (Mager et al, 2005)

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Conclusion