We’ve heard a lot recently about how important phage biocontrol could be to agriculture, and every phage conference seems to have at least a talk or two on using phages in agriculture. This week, we’re delving into a study published earlier this year, where a Salmonella phage cocktail was used in a farm setting to test its ability to control Salmonella in chickens.
The main source for this issue is: Clavijo, V. et al.(2019)
How bad is Salmonella?
Salmonella kills over 150,000 people a year, and infects over 90 million. Also, antibiotic resistance is a big problem with Salmonella.
How is Salmonella controlled in farms, currently?
Currently, it’s done in a multifactorial way, via antibiotics, vaccines, probiotics, prebiotics, and more.
However, as it’s becoming increasingly important that antibiotic use in agriculture is reduced, there’s an increasing need to find alternatives. Otherwise, we’ll see a rise in foodborne illness, and farmers will see big losses in productivity at the same time.
Have phages been tested in chickens before?
Yes, this has been done for decades, and has been reviewed extensively. However, most of these studies have been done using phages to target chickens in experimental settings, and not out in the field/on farms.
What’s hard about treating chickens with phages?
- Phage specificity is a problem (need broad host-range cocktails)
- A high enough phage inoculum can be hard to achieve (phages are usually given to chickens orally through drinking water, so high phage titres are needed)
- Density of bacteria needs to be high enough to support phage replication (but waiting too long for bacterial densities to get high enough can mean there’s no time to treat with phages before chickens are slaughtered)
- Studies in farms tend to lead to cross-contamination of phages between control and experimental groups, making data analysis a challenge
What’s nice about treating chickens with phages?
- Cost-effective
- Considered to be safe
- Phage dosing can easily be carried out by farmers
The study
Clavijo, V., Baquero, D., Hernandez, S., Farfan, J. C., Arias, J., Arévalo, A., Donado-Godoy, P., & Vives-Flores, M. (2019). Phage cocktail SalmoFREE® reduces Salmonella on a commercial broiler farm. Poultry Science. DOI: 10.3382/ps/pez251
What they did and what they found
They used a 6-phage cocktail to treat Salmonella-colonized chicken flocks on a commercial Colombian chicken farm. They did two trials with about 30,000 chickens involved in each. They dosed the phages via drinking water (and had control groups for each), and they compared Salmonella incidence across groups. They found that the phages reduced Salmonella incidence, and that the treatment was safe.
Tell us about the phage cocktail used
The cocktail used was a 6-phage cocktail called SalmoFREE, produced and recently patented by the authors, and set to be commercialized by SciPhage, a spin-off company which works toward the development of phage therapy in Colombia (Viviana and Martha, two of the authors of this study, are part of the company).
Prior to this study, data about the cocktail’s phages (including genome sequence, host range, in vitro efficiency, and stability in chlorinated water) had already been documented.
A safety trial had already been carried out using chickens reared in battery cages (controlled conditions; not on a farm), where SalmoFREE® was given to chickens via drinking water. (The cocktail was found to be safe, as they saw no differences in mortality, weight gain, or feed intake.)
How was the dosing done?
They administered 3 doses of phages through drinking water (10^8 PFU/mL for 2.5 h; each chicken got around 30-60 mL per dose on average, dosing done on day 18, 27 and 35).
What kind of ethics approval did they need?
This study was approved by the Institutional Committee on Care and Use of Experimental Animals (CICUAL) from the Universidad de los Andes.
Why was this study different?
It took place on an actual farm, making it one of the first studies of its kind using phages. The only other one they point to was done with Campylobacter phages in Germany by Sophie Kittler and colleagues.
Did anything go wrong?
They ran into a few challenges. First, antibiotics were given to the chickens in their experimental group in the first of their two studies, since the veterinarian caring for them was concerned about increased mortality in one of the two experimental group houses (prior to phage treatment). So it was impossible to attribute Salmonella reduction in those chickens to the phages alone (although 3 days after antibiotics were given, they still detected lots of Salmonella, suggesting that those antibiotics were not effective against the organism).
Another challenge was that samples were spilled on the final day of the second study, so they didn’t get numbers from the final data point.
Another challenge was that they detected phages in the control chicken houses, suggesting cross-contamination of the phages (perhaps due to rubber boots of workers). (This was apparently also seen in the Kittler study).
They also detected phages in the control and experimental chicken houses at the beginning of trial #2 (done at the same farm as trial #1), meaning it was difficult to draw conclusions from the second trial.
Did the phages work?
Their cocktail appeared to reduce Salmonella incidence by up to 100%, though because of the issues described above, the phage treatment could only be partially attributed to the reduction.
Was it safe?
The phages didn’t appear to affect production parameters like chicken weight gain, feed conversion, weight homogeneity, or mortality rate, meaning it could be considered “innocuous”. In other words, the chickens seemed fine.
What does this all mean?
The safety and efficacy the authors observed is good news for their cocktail. Additionally, this study will help inform design of future trials for testing phage cocktails in poultry in the field, which have thus far been scarce. Lastly, the authors note that doing this study built trust with commercial poultry farmers, which is not to be understated, since adoption by farmers will likely be key to the success of any phage product.
It remains to be seen whether the levels of reduction these authors observed will lead to reduced food poisoning among consumers, though a reduction of even 50% at the pre-harvest stage has been predicted to prevent introduction of Salmonella into the food chain.
Main source for this issue
Clavijo, V., Baquero, D., Hernandez, S., Farfan, J. C., Arias, J., Arévalo, A., Donado-Godoy, P., & Vives-Flores, M. (2019). Phage cocktail SalmoFREE® reduces Salmonella on a commercial broiler farm. Poultry Science. DOI: 10.3382/ps/pez251
Other sources & further reading
Cover Photo by William Moreland on Unsplash
