Streptococcus australis and Ralstonia pickettii as Major Microbiota in Mesotheliomas

Our plain-English summary of Streptococcus australis and Ralstonia pickettii as Major Microbiota in Mesotheliomas, by R. Higuchi, T. Goto, Y. Hirotsu, et al (Journal of Personalized Medicine, 2021).

The study

• Authors: R. Higuchi, T. Goto, Y. Hirotsu, S. Otake, T. Oyama, K. Amemiya, H. Mochizuki, M. Omata
• Journal: Journal of Personalized Medicine
• Published: 2021;11(4)
• Cited by: 19 articles, as counted by NIH iCite
• Read it: PubMed · Publisher · Free full text

Abstract

The microbiota has been reported to be correlated with carcinogenesis and cancer progression. However, its involvement in the pathology of mesothelioma remains unknown. In this study, we aimed to identify mesothelioma-specific microbiota using resected or biopsied mesothelioma samples. Eight mesothelioma tissue samples were analyzed via polymerase chain reaction (PCR) amplification and 16S rRNA gene sequencing. The operational taxonomic units (OTUs) of the effective tags were analyzed in order to determine the taxon composition of each sample. For the three patients who underwent extra pleural pneumonectomy, normal peripheral lung tissues adjacent to the tumor were also included, and the same analysis was performed. In total, 61 OTUs were identified in the tumor and lung tissues, which were classified into 36 species. Streptococcus australis and Ralstonia pickettii were identified as abundant species in almost all tumor and lung samples. Streptococcus australis and Ralstonia pickettii were found to comprise mesothelioma-specific microbiota involved in tumor progression; thus, they could serve as targets for the prevention of mesothelioma.

In plain English

This exploratory study from Yamanashi Central Hospital, Japan, looked for bacteria in mesothelioma tissue. The authors sequenced a bacterial gene (16S rRNA) in stored tissue from eight men who had surgery for mesothelioma. For the three who had extrapleural pneumonectomy, normal lung tissue next to the tumor was also tested, giving 11 samples. Tumor tissue from 19 thymoma patients served as a comparison. The article did not report the patients' asbestos exposure. Among sequences classifiable to species, Streptococcus australis and Ralstonia pickettii had the highest average relative abundance across the 11 samples, 32.2% and 24.4%, with wide variation between samples (plus or minus 29.6% and 21.1%). One passage places both in tumor tissue from six patients and all three lung samples; another says all mesothelioma tissues. Neither was detected in the thymoma samples. The authors concluded that these are two mesothelioma-specific species and suggested they might one day be targets for prevention. They noted the small, all-Japanese patient group, and that their observational design cannot show whether the bacteria cause the cancer or merely reflect the disease.

We wrote this plain-English summary from the full article with the help of AI, and a second AI model checked each sentence against the article. It is not the authors' wording; the abstract and the article are their own account.

What the study did and found

• Design: Exploratory observational laboratory study: bacterial 16S rRNA gene sequencing of preserved tumor tissue, with thymoma tissue as a comparison group
• Who was studied: Eight patients who had surgery for mesothelioma at Yamanashi Central Hospital, Japan. The Methods give January 2016 to August 2020; the Results give January 2014 to August 2020. All were male, seven were smokers, ages were 53 to 78, and histology was six epithelioid, one sarcomatoid and one biphasic. There were 11 specimens in total: 8 tumors plus adjacent normal lung from the 3 patients who had extrapleural pneumonectomy. The comparison group was tumor tissue from 19 thymoma patients.
• Exposure: The study examined bacteria present in tissue, not asbestos. The article did not report asbestos exposure information for the patients. Asbestos appears only in the discussion, as part of a hypothesis.
• Main results:
  • 61 operational taxonomic units (bacterial groupings) were detected across the 11 mesothelioma and lung samples.
  • Among classifiable sequences, the two predominant species across the 11 samples were Streptococcus australis, with an average relative abundance of 32.2% (plus or minus 29.6%), and Ralstonia pickettii, at 24.4% (plus or minus 21.1%). These are relative abundances from 16S sequencing and varied widely between samples.
  • Both species were reported in the tumor tissue of six patients and in the normal lung tissue of all three patients who had extrapleural pneumonectomy. The same paragraph also states they were found in all mesothelioma tissues.
  • Neither Streptococcus australis nor Ralstonia pickettii was detected in the 19 thymoma samples. The authors took this to suggest the species are specific to mesothelioma.
• The authors' conclusion: The authors concluded that they had identified two mesothelioma-specific species, Streptococcus australis and Ralstonia pickettii. They said further research is needed on how these bacteria relate to cancer development. They suggested that controlling the bacteria, for example with antibiotics or vaccines, might in future help prevent mesothelioma.
• Limitations the authors state:
  • The number of patients was small because the tumor is rare, and all patients were Japanese.
  • No blood samples were analyzed for these bacteria.
  • Because the design was observational, it is unclear whether the bacteria are causally linked to cancer development or only reflect disease processes.
  • A larger series of patients is needed.

Topics

Medical terms in this study, explained in our Lexicon: Mesothelioma, Carcinogenesis, Pathology, Pneumonectomy.

Related studies

• A gut microbiota rheostat forecasts responsiveness to PD-L1 and VEGF blockade in mesothelioma — M. Zhang, A. Bzura, et al. (2024)
• Pleural fluid microbiota as a biomarker for malignancy and prognosis — B. Kwok, B.G. Wu, et al. (2023)
• Intratumor microbiota as a novel potential prognostic indicator in mesothelioma — F. Pentimalli, M. Krstic-Demonacos, et al. (2023)
• Airways microbiota: Hidden Trojan horses in asbestos exposed individuals? — D.E. Magouliotis, V.S. Tasiopoulou, et al. (2014)
• Causal effect of gut microbiota on the risk of cancer and potential mediation by inflammatory proteins — Y. Wang, W. Liu, et al. (2025)
• Bidirectional Mendelian randomization and potential mechanistic insights into the causal relationship between gut microbiota and malignant mesothelioma — Y. Zhou, H. Zhu, et al. (2025)

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