Written by Shrey Mehta ‘26
Edited by Yuliya Velhan ‘25
Figure 1: Bacterial colonies presented on a petri dish with media
Bacteria, good or bad, are everywhere, and often strike when we least expect it.
An important week of exams.
A birthday party.
An amusement park field trip.
Because bacterial infections are so common throughout the aging general public, we may unintentionally overlook their true severity and intensity. While most medications can resolve common bacterial infection in a short amount of time, some of these tricky and evasive pathogens have the ability to survive capable therapeutics and cause consequences that we most likely don’t consider on a daily basis.
The foremost being cancer.
A Background: The Overall Intersection of Bacteria and Cancer
As of recently, researchers are putting more focus on bacterial infections as significant risk factors for developing cancer. Indeed, the ability of bacteria to resist therapies and remain dormant in the body can strain the immune system to great extents, ultimately leading to cancer.
Importantly, we must quickly summarize our current understanding of how cancer develops. Cancer results from a series of genetic and epigenetic changes that disrupt cellular homeostasis (growth, control, and survival). Many factors can lead to this drastic disruption, such as genetic mutations, errors in DNA replication, severe inflammatory responses, radiation, etc. Intriguingly, infectious pathogens, like bacteria, account for approximately 20% of all human tumors! These pathogens, especially those with the selective traits to evade medicine, cause such a great degree of chronic inflammation, which ultimately leads to uncontrollable cell proliferation: the hallmark of cancer.
We must also not forget that bacteria naturally exist in our bodies since birth, creating a mutually beneficial microbial environment that actually aids in many human functions! However, even this coexistence does not always remain in harmony; an imbalance in host-bacterial interactions can change the physiological equilibrium in those host cells, leading to many severe conditions like malnutrition and cancer.
Bacterial Infection: From the Onset to Further Development of Cancer
Thus far, researchers have studied the link between bacterial infection as potential carcinogens and tumor promoters. In most of the examples explored below, the main contributors to cancer appear to be bacterial toxins, enzymes, and oncogenic peptides that interfere with the cell cycle, disrupt signaling pathways, and strain the host immune system!
One of the most well-researched interplays between bacteria and cancer is the Helicobacter pylori infection and gastric cancer. This specific bacteria type actually has a very long co-evolutionary relationship with early human populations, and in some areas of the world, H. pylori infection is significantly associated with gastric cancer risk. The potential cancer-causing-mechanism appears to be persistent inflammation of the gastric mucosa, which ultimately damages epithelial cells and suppresses the immune system.
Another prime example of this interplay comes from common oral bacterial infections, which typically manifest as periodontal diseases. Once again, such diseases are linked to long-term inflammation which could lead to cancers of the throat. Intriguingly, these bacteria also have the ability to cause issues in different organs from the body through damaged periodontal tissues!
Finally, research has also shown that lung cancer, gallbladder cancer, and cervical cancer are implicated by various bacterial infections, especially ones most commonly known to the public like Salmonella and E. coli infections! The figure below goes into a little more depth on the exact mechanism through which bacteria byproducts or activities in the host body can lead to tumor growth!
S;, Yusuf K;Sampath V;Umar. “Bacterial Infections and Cancer: Exploring This Association and Its Implications for Cancer Patients.” International Journal of Molecular Sciences, U.S. National Library of Medicine, https://pubmed.ncbi.nlm.nih.gov/36834525/.
Sajmina Khatun, et al. “The Role Played by Bacterial Infections in the Onset and Metastasis of Cancer.” Current Research in Microbial Sciences, Elsevier, 26 Oct. 2021, https://reader.elsevier.com/reader/sd/pii/S2666517421000584?token=3F13BF17B4B43F36AA2584DEB0B37C2E3F3C965B310BBC93C2E72B36D3B0277013641AEDDA3314CC5ABC7B5028711F1D&originRegion=us-east-1&originCreation=20230312201130.
Bose, Dr. Priyom. “The Role of Bacteria in Cancer Growth.” News, 21 Nov. 2022, https://www.news-medical.net/news/20221120/The-role-of-bacteria-in-cancer-growth.aspx.
Bessède, E, et al. “Helicobacter Pylori Infection and Stem Cells at the Origin of Gastric Cancer.” Nature News, Nature Publishing Group, 21 July 2014, https://www.nature.com/articles/onc2014187.
Nalbandian, A, et al. “Lung Carcinogenesis Induced by Chronic Tuberculosis Infection: The Experimental Model and Genetic Control.” Nature News, Nature Publishing Group, 30 Mar. 2009, https://www.nature.com/articles/onc200932.