Salmonella is just one of the genera of bacteria that we have covered so far in microbiology.

Dr Krishnan demonstrated how it is related to the ingestion of food and water which has been contaminated by human and animal waste. It is frequently associated with poultry, eggs or even inadequately cooked meat products. Some important and distinguishing features of Salmonella include the fact that they are gram-negative rods, they do not ferment lactose and they do produce hydrogen sulfide. There are three antigens which are important for taxonomic and epidemiological purposes: the cell wall O, flagellar H and capsular Vi. Enterocolitis is a syndrome which is characterized by an invasion of the epithelial and sub-epithelial tissue of the small and large intestines. The Salmonella organisms penetrate both through and between the mucosal cells and spread into the lamina propria. This ultimately results in inflammation and diarrhea. Gastric acid is one of the most important host defences in this scenario, and if the patient has had a gastrectomy or uses antacids, they are much more susceptible as the infectious dose is significantly lowered.

Typhoid fever, while relatively rare in the United States, is still quite prevalent in developing countries characterized by rose coloured spots. The bacteria invades the small intestine and enters the bloodstream. The bacteria is carried by white blood cells in the spleen, liver and bone marrow where they multiply and move to invade the gallbladder, biliary system and lymphatic tissue of the bowel. Patients may present with poor appetite, fever as high as 104 degrees Fahrenheit, lethargy, diarrhea, and generalized aches and pains. Fatality rates could be as high as 20% without antibiotic treatment. While everything mentioned up until this point in this article has been negative and detrimental to human health, new evidence has emerged where Salmonella can play a huge to battle other ailments. Posted less than a week ago, Zheng and his team have published a paper, indicating they have genetically manipulated a version of Salmonella typhimurium which acts as a potent destroyer of mouse tumours. Susan Edman has commented on the work, claiming it is “part of a promising frontier in using bacteria or their products to stimulate beneficial host immune responses to inhibit and suppress cancer development and growth.”

Tumors are known to often have oxygen- starved and necrotic cores, which are essentially excellent environments for anaerobic bacteria such as Listeria, Clostridium, and Salmonella. Upon genetic engineering, these bacterias may be triggered to to kill cancer cells, while simultaneously attraction the attention of the body’s own immune system which leads to further destruction. Although this research is still in its infancy, riddled with problems pertaining to containing the strains of bacteria with antibiotics and ignorance regarding the exact mechanism of how the bacteria kills the cancer cells, this is an excellent stride for science in the battle with cancer. Going back to the late 1800s, William Coley pioneered the use of bacteria as a cancer treatment upon the discovery that one of his cancer patients survived longer than expected, which was tied to the bacterial infection he suffered from. Today’s renaissance of the use of bacteria as therapy is very promising, and hopefully in the near future, we can reduce the prevalence of cancer, as it is still one of the leading causes of death in the developed world.

Source: J.H. Zheng et al., “Two-step enhanced cancer immunotherapy with engineered Salmonella typhimurium secreting heterologous flagellin,” Science Translational Medicine, 9, eaak9537, 201

– Margarita Toufeili
MD3 MICROBIOLOGY