Applied Microbiology: Open Access
Open Access

The Adaptive Conditions for Ambient Microbiome

Vincent Horndler^{* *}Correspondence: Vincent Horndler, Department of Microbiology, University of Queensland, Brisbane, Australia, Email:

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Description

The identification of the microbiome (its polymorphic microorganisms) as a new emerging characteristic of cancer reflects a large corpus of fast expanding study. Microbes may be directly carcinogenic, influence host immunological responses to induce malignancy, and be critical effectors in deciding anticancer therapeutic success. Manipulation of the microbiota shows promise as a means of influencing cancer outcomes. The inclusion of polymorphic microorganisms reflects a growing recognition that the complex microbial ecosystems (or microbiome)-which includes bacteria, fungi, and viruses that live in symbiotic relationships with the human body-have a significant influence on cancer pathogenesis. The microbiome currently appears to have a significant role in carcinogenesis, cancer differentiation, and malignant development.

Moreover, the microbiome interacts directly, both favourably and negatively, with other well-known cancer hallmarks such as tumour inflammation, immune destruction, genomic instability, and resistance to anticancer therapy. The study of bacteria in the gastrointestinal tract (gut microbiome), which is the most fully studied region, provides the most important evidence for this integrated involvement. However, there has lately been an increasing recognition of the significance of polymorphic microorganisms in other tissues/organs, such as those found on different mucosal surfaces and/or in touch with the external environment (skin, genitourinary tract, and lung), as well as those found within tumours (intratumoural microbiome). The human body is thought to contain bacteria, with the total microbial genome-or metagenome-outnumbering the human genome by a ratio of more than 100. Bacteria in the colon make up over 97% of the microbiome, and this high density is thought to be responsible for the majority of the known microbial immunomodulatory effects. Growing data suggests that polymorphic microorganisms in the gut play an important role in cancer pathogenesis, from carcinogenesis to influencing the success of anticancer treatment.

Functional experiments using Faecal Microbiota Transplantation (FMTs) from colorectal cancer patients into recipient mice predisposed to acquire colon cancer confirmed the idea that microorganisms had both tumor-promoting and cancer-protective properties. Furthermore, dysbiosis, or disruption of the intestinal microbial community induced by illness or antibiotic therapy, has been repeatedly associated to cancer in the colon and beyond. Despite this obvious separation, only 11 of the estimated 1012 different microbial species on Earth have been discovered as direct human carcinogens (oncomicrobes); for example, certain strains of Escherichia coli create colibactin, a strong DNA alkylator associated to colorectal cancer. More commonly, gut bacteria are ‘complicit’, unable to induce carcinogenesis on their own while promoting other cancer characteristics. Bacteroides fragilis generates toxins that attach to the surface of colonic epithelial cells, boosting proliferative signalling and causing colon cancer formation. Bacteria may collaborate in a ‘driverpassenger’ relationship to initiate and sustain carcinogenesis; in this case, B. fragilis (driver) promotes carcinogenesis by altering the colonic milieu, enabling opportunistic commensal bacteria like Streptococcus gallolyticus (passenger) to take over and further slow carcinogenic development.

The role of gut microorganisms on systemic immunity is well supported by preclinical and clinical studies. The gut microbiome has been demonstrated to have a wide impact on both adaptive and innate immune systems, resulting in the development of a vast repertoire of chemokines and cytokines associated with the formation of both tumor-promoting and tumor-antagonizing immunological microenvironments. Similarly, individual patients' distinct microbiomes modulate other cancer hallmarks such as tumour inflammation, evasion of adaptive immune destruction, and responsiveness to anticancer therapies (example: Immune Checkpoint Inhibitors (ICIs)), providing insight into modulation as a potential anticancer therapeutic strategy. Different bacteria colonise all tissues and organs exposed to the external environment.

The microbiotas present in these places vary significantly depending on a variety of characteristics such as gender, age, and environment. In contrast to the gut, where the symbiotic interaction between microbiota and host is more fully defined, the normal and harmful functions of microbiota in cancer are still being explored. However, there is growing evidence that microorganisms present in tissue-specific microbiomes (for example, in the vagina) may either contribute to the development of cancer or defend against it. Polymorphic microorganisms may have an important role in the development, progression, and response to therapy of malignancies. The inclusion of microorganisms as a new developing and enabling cancer characteristic indicates a growing awareness and appreciation of the important role bacteria play in cancer. Greater understanding may provide for opportunities to enhance each step of the cancer care cycle, from prevention through advanced disease therapy.