We have discussed the association of salmonella typhi with gallbladder cancer in the last post. Let’s look at more examples on this topic.
Helicobacter pylori is linked to both gastric cancer and
MALT lymphoma (a form of lymphoma involving the mucosa-associated
lymphoid tissue, often in the stomach); Chlamydia pneumoniae to lung cancer; Streptococcus bovis and/or Enteroccocus faecalis to colon cancer.
Although research has shown that certain bacteria are associated with
human cancers, their role in cancer is of complex. Convincing evidence
links some species to the formation of cancer while others appear
promising in the diagnosis, prevention or treatment of cancers. However,
you might wonder how bacteria infection could lead to cancer. Here I
provide you some insights.
Bacteria may cause cancer through:
1. Chronic infection. Some bacterial toxins can
negatively impact the process that controls the normal cell cycle and
cell growth, others disrupt the cellular signaling pathways that
regulate normal cell death, consequently promoting cancerous growth. In
addition, infection-induced immune response may release immune
modulating substances from inflammatory cells, contributing to
carcinogenesis.
2. DNA damage. Bacteria can produce free radicals –
very unstable but highly reactive with other molecules. They can bind to
DNA and cause DNA mutation, thereby altering the genes that control
normal cell division and cell death. Cancer is initiated when
uncontrolled growth of abnormal cells takes place.
3. Weakened or suppressed immune system.
The immune system is an important line of defense for any toxins or
diseases including cancer. Toxins or pathogens sometimes can get away
from the host’s immune system to survive, and then modify one’s immune
function. When its function is compromised, the immune system no longer
recognizes and fights bacteria or toxins as foreign bodies, nor gets rid
of them.
That being said, don’t panic. A majority of individuals will not
develop cancer after infection by a cancer-causing agent. However, be
conscious and alert. The facts are:
- Certain individuals are more susceptible to cancer-causing infections.
- Incidence of certain cancers may vary among populations or geographic regions.
- It often takes years or decades between acquiring the infection and getting cancer.
Take-home-message:
Chronic infection is a risk factor for cancer. Staying away from or treating the infection may prevent it.
Photo illustration: Color-enhanced scanning electron micrograph showing Salmonella typhimurium (red) invading cultured human cells
Photo credit: Rocky Mountain Laboratories, NIAID, NIH
