Phage Therapy: The New Battle Against Salmonella
By Elaney Marcotte
Have you ever been told not to eat raw cookie dough? This is because of the bacteria Salmonella that can be found in raw eggs. Salmonella is a prime example of a disease that is spread from animals to humans, usually through contaminated meat and eggs (1). Salmonella infects the digestive tract of mammals, giving you symptoms normally associated with food-poisoning (1). The CDC estimates that there have been over 1.2 million infections and 450 deaths from Salmonella enterica per year in the United States (1).
Often, the treatment for Salmonella is antibiotics. However, certain strains of Salmonella have evolved to be resistant to antibiotic treatments (2). With the increase in antibiotic resistant bacteria causing many medications to be ineffective, scientists needed to find an alternative treatment to Salmonella (2).
A potential solution to this problem is found in an unexpected place; viruses. Bacteriophage, which are viruses that infect bacteria, are used to combat antibiotic resistant bacteria through a process called “phage therapy”. Phage therapy consists of introducing a bacteriophage into a sick host in order to kill the bacterial infection. Each species of bacteriophage infects a bacteria host and kills it, while leaving the animal unaffected. This method of combating bacteria targets only a small amount of bacteria species, unlike antibiotics which can kill a wide range of bacteria and can destroy beneficial gut microbes (3).
In a recent study, M. Ahmadi and collaborators isolated a new bacteriophage, named PSE, that infects Salmonella enteritidis (2). In order to kill Salmonella, bacteriophage must be able to survive in the harsh conditions of the gut (2). PSE remained stable even when exposed to salts, temperatures, and pHs that mimic the conditions of the digestive tract, showing that it has the potential to be used as a treatment (2). This bacteriophage also reduces the growth and overall count of Salmonella when tested in quails. PSE is one of the many bacteriophages that successfully reduce Salmonella colonization, and one of the first to be stable enough to survive in poultry (2,3,4).
Phage therapy testing on PSE reveals important information on the most effective administration of bacteriophages. One of the main problems with implementing phage therapy in the past was knowing how and when to administer the bacteriophage to poultry to produce the most effective result (2). Tests on PSE reveal that administration of bacteriophages as a preventative measure is more effective than using the bacteriophage to reduce Salmonella after infection (2). PSE persisted in quails before Salmonella was introduced, meaning that it can be administered prophylactically to prevent Salmonella growth (2).
Tests with PSE also show the best method to administer PSE to poultry. Oral administration of PSE causes the largest reduction in the colonization of Salmonella (2). This encourages the development of oral administration of phages for phage therapy for both poultry and humans. With these results, phage therapy is moving one step closer to being used in more poultry farms.
While phage therapy seems promising, there are still a few limitations to this process. Some bacteriophage can only target one species of bacteria (3). This can cause treatments to have to include a combination of phage or for a person to have to receive multiple treatments over time. In addition, not all phage are able to survive in animal hosts, so phage need to undergo a lot of tests in vitro before they can be used in vivo. Phage therapy is still under testing and refinement, and more bacteriophages are being isolated before this practice is applied to large-scale poultry farms (2).
With further development, administering bacteriophages to poultry populations may help to reduce or eliminate Salmonella. Phage therapy may also become a future solution to fighting antibiotic resistance for a wide range of bacterial diseases. In the fight against Salmonella, phage therapy may bring us closer to a victory.
For further reading
1. CDC Salmonella ttps://www.cdc.gov/salmonella/index.html
2. (Main Research Article) Ahmadi M, Karimi Torshizi MA, Rahimi S, Dennehy JJ. Prophylactic Bacteriophage Administration More Effective than Post-infection Administration in Reducing Salmonella enterica serovar Enteritidis Shedding in Quail. Front Microbiol. 2016;7. doi:10.3389/fmicb.2016.01253
3. Atterbury RJ, Bergen MAPV, Ortiz F, Lovell MA, Harris JA, Boer AD, et al. Bacteriophage Therapy To Reduce Salmonella Colonization of Broiler Chickens. Appl Environ Microbiol. 2007;73: 4543–4549. doi:10.1128/AEM.00049-07
4. Sillankorva S, Pleteneva E, Shaburova O, Santos S, Carvalho C, Azeredo J, et al. Salmonella Enteritidis bacteriophage candidates for phage therapy of poultry. J Appl Microbiol. 2010;108: 1175–1186. doi:10.1111/j.1365-2672.2009.04549.x
Laney Marcotte (’18) is a junior at Bucknell University working towards a B.S in Biology and a minor in Mathematics.
At Bucknell, Laney is an outdoor pre-orientation trip leader, the student manager of the Challenge Course, and is part of the varsity women’s rowing team. She was also part of a research class at Bucknell that spent a year isolating, purifying, and annotating the genome of novel bacteriophage.
Laney recently returned from studying abroad in Australia where she assisted with field research for a month on Devil Facial Tumor disease in Tasmanian Devils.
After college, Laney is interested in pursuing a career involving animals, and plans to attend graduate school. She hopes to one day return to Australia to work with marsupials.