口腔内の歯周病菌が大腸がん発生に関与

横浜市立大学肝胆膵消化器病学内視鏡センター診療講師の日暮琢磨氏らは、大腸がん患者の患部組織と唾液から口腔常在菌の一種であるFusobacterium nucleatum（F. nucleatum）を分離、解析したところ、患者の4割以上でがん組織と唾液に共通する菌株が存在したことをGut（2018年6月22日オンライン版）で報告した。同氏は「この結果から、大腸がん組織中のF. nucleatumが口腔内に由来することが示唆された」と述べている。

口腔内のF. nucleatumが大腸がん組織へ移行

近年、大腸がんの病態や予後にF. nucleatumが悪影響を及ぼすという報告が増え、注目されている。しかし、これまでヒトの腸内からF. nucleatumが検出されることは少なく、大腸がん組織におけるF. nucleatumの感染経路は不明だった。

　日暮氏らは、F. nucleatumが口腔内環境において優先菌種であることに着目し、口腔内に存在するF. nucleatumが大腸がん組織へ移行しているとの仮説を立てて検証を行った。

　同氏らは、大腸内視鏡検査で大腸がんと診断された84例のうち、1カ月以内の抗菌薬使用歴がないなどの条件を満たした患者14例（男性10例、女性4例、平均年齢69.4歳）を対象に、内視鏡を用いて採取した大腸がん組織および唾液検体からFusobacterium選択培地を用いて計1,351コロニーを分離、特異的プライマーポリメラーゼ連鎖反応（PCR）法で361のF. nucleatumを検出した。

　その結果、8例で大腸がん組織および唾液の両方からF. nucleatumが検出された。さらに、これら8例から分離されたF. nucleatumをarbitrarily primed PCR（AP-PCR）法を用いて菌株レベルで解析したところ、6例において大腸がん組織および唾液の両方から同一菌株が検出された。

　以上から、同氏は「F. nucleatumは健康人の多くが口腔内に保有する常在菌の一種であり、歯周病の悪化にも関与することが報告されており、近年では大腸がん悪化への関与が強く疑われることも報告されている。今回の研究の結果、口腔内と大腸がん組織におけるF. nucleatumの菌株が一致したことから、口腔内のF. nucleatumが大腸がん組織に移行、感染していることが示唆された」と結論した。

　さらに「詳細な移行・感染ルートの解明は今後の課題であるが、今回得られた知見により、口腔内や腸内の細菌を調べることで大腸がんの簡便な診断法を開発できる可能性や、口腔内、腸内細菌を制御することが大腸がんの治療や予防につながる可能性が示唆された。今後は分子生物学的手法も取り入れて、より多くの大腸がん患者を対象に研究を進めて行く予定だ」と展望した。

Patients with colorectal cancer have identical strains of Fusobacterium nucleatum in their colorectal cancer and oral cavity

Yasuhiko Komiya ^{1 2}, Yumi Shimomura ³, Takuma Higurashi ¹, Yutaka Sugi ³, Jun Arimoto ¹, Shotaro Umezawa ¹, Shiori Uchiyama ¹, Mitsuharu Matsumoto ³, Atsushi Nakajima ¹

• PMID: 29934439

• PMCID: PMC6582823

• DOI: 10.1136/gutjnl-2018-316661

Gut 2019 Jul;68(7):1335-1337. doi: 10.1136/gutjnl-2018-316661.Epub 2018 Jun 22.

https://pubmed.ncbi.nlm.nih.gov/29934439/

We read with great interest the article by Flemer et al, which suggests that analysis of the oral microbiota could potentially be used as a screening method for colorectal cancer (CRC) and polyp detection.¹ Fusobacterium (F.) nucleatum is one of the most densely colonised bacterial species in the oral cavity and is known to be associated with periodontitis.² Recently, many researchers have demonstrated that F. nucleatum is related to CRC development and pathogenicity.^{3 4} However, the relationship between F. nucleatum in CRC and the oral cavity is not well understood. For this purpose, we examined whether identical strains of F. nucleatum could be isolated from CRC and saliva specimens obtained from the same patient. The approach used in this study is detailed in figure 1A (see online supplementary information for details). We collected CRC and saliva samples from 14 patients (online supplementary table 1) and isolated bacteria from the specimens on Fusobacterium-selective agar. All colonies (1,351 in total) were analysed by PCR using F. nucleatum-specific primer sets, and 361 F. nucleatum isolates were obtained. F. nucleatumwas detected in 8 of 14 patients (57.1%) from CRC samples and in all patients (100%) from saliva samples (figure 1B). The F. nucleatum subspecies identified by 16S rRNA gene sequencing and the number of isolates from each specimen are shown in table 1.

Figure 1

Detection of Fusobacterium nucleatum subspecies in paired colorectal cancer and saliva samples. (A) Schematic of the experimental procedures. AP-PCR, arbitrarily primed PCR; CRC, colorectal cancer; Fn, Fusobacterium nucleatum. See online supplementary information for more details. (B) Flowchart of the study process. FS agar, Fusobacterium-selective agar. (C) AP-PCR patterns detected with primer D11344. Data are representative of at least two independent experiments. Identical pairs are highlighted in yellow or blue. GL, gene ladder (0.1, 0.2, 0.3, 0.4, 0.5, 0.7, 1.0, 1.3, 1.5, 2.0, 3.0, 4.0, 5.0, 7.0, 10 and 20 kbp). Subspecies, an, nu, po and vi are F. nucleatum subsp. animalis, F. nucleatum subsp. nucleatum, F. nucleatum subsp. polymorphum and F. nucleatum subsp. vincentii, respectively.

Four subspecies, F. nucleatum subsp. animalis, F. nucleatum subsp. nucleatum, F. nucleatum subsp. polymorphum and F. nucleatum subsp. vincentii were isolated from the samples. To identify F. nucleatum isolates from CRC and saliva at the strain level, we performed arbitrarily primed PCR (AP-PCR) as the strain typing method, which can be applied without genome information or specialised techniques and equipment.^5–7 We performed AP-PCR targeting the F. nucleatum isolates from the 8 patients whose CRC and saliva samples were both F. nucleatum-positive and analysed the detected AP-PCR patterns (figure 1C and online supplementary figure 1). Focusing on patient C (left, bottom), there were no common isolates between their CRC and saliva samples (figure 1C). However, patient D (left, top) had two and four strains of F. nucleatum subsp. animalis detected in their CRC and saliva, respectively. Furthermore, strains A2 and A3 (highlighted in yellow and blue) were indicated as identical strains by the AP-PCR patterns (figure 1C). We detected identical F. nucleatum strains in both CRC and saliva from 42.9% (6/14) of the patients. Notably, an identical strain was detected in 75% (6/8) of patients who were both F. nucleatum-positive in CRC and saliva specimens. From our results, there were no significant differences in the detection rate of F. nucleatum among each lesion site from the 8 patients. F. nucleatum was detected from stages 0 to IV (online supplementary table 1), indicating that F. nucleatumcould adhere to CRC tissue from an early stage of tumorigenesis, as previously reported.^{8 9} From our results,more than 40% of CRC patients exhibited identical strains of F. nucleatum in their CRC and saliva specimens. This suggests that F. nucleatum in CRC originates in the oral cavity. Our findings support that targeting F. nucleatum in the oral cavity may provide insights for further studies in the field of human microbiome research and CRC.

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