Dr. John Prescott

Dr. Prescott has been a professor at the University of Guelph for over 35 years and although he has recently retired, he is continuing to wrap up and finish the research projects he was working on. For the last 7-8 years he has focused on poultry and necrotic enteritis specifically. Prescott is a trained veterinary bacteriologist. He obtained his vet degree from the University of Cambridge in England in 1973, followed by his Ph.D. in 1977. Prescott came to the University of Guelph in 1976 and first worked in the diagnostic lab for a few years before taking a position as a professor and pursuing a career in teaching and research.

Fostering expertise in the industry

Through the years at the University of Guelph, Prescott’s research program has helped to train over 35 M.Sc. and Ph.D. students. A few of these, including two of Prescott’s Ph.D. students Dion Lepp and Ravi Kulkarni, are still involved in the poultry industry or poultry research today. Lepp is continuing to conduct research on priority issues for the poultry industry through his position with Agriculture and Agri-Food Canada. Kulkarni is now working as the coordinator with the Poultry Health Research Network based out of the University of Guelph.

Highlights of research outcomes

Prescott’s research program in recent years focussed on Clostridium perfringens, the causative agent of necrotic enteritis (NE). C. perfringens is a highly important bacterial disease of poultry, estimated to cost the broiler industry globally about $6 billion in terms of costs of prevention and disease. Traditionally it has been controlled by administration of preventive antibiotics. However, the desire to reduce antibiotic use in food animal production globally has led to a surge of research worldwide on NE and on alternative approaches to its control, vaccination being one of them.

There is an amazing amount of collaboration among researchers around the world working on this important issue. In fact, to bring all these experts together, Prescott initiated and helped organize an international conference in Denmark in 2015 focussed exclusively NE. The conference was a huge success, with considerable value in the discussions among attendees and the ideas generated from it.

The overall goal of Prescott’s research on NE has been to gain a better understanding of the disease, to understand the detailed process of how C. perfringens causes NE, to find the weak points of the bacteria to know how it can be controlled, and to try and produce a vaccine for it.

Prescott’s work on this progressed in what could be considered three phases. In the first phase his group demonstrated that, in principle, it was indeed possible to immunize against C. perfringens. Then they did a great deal of work to find what material or substrate to immunize with. Two antigens were identified as the best candidates for immunization, and these are the ones that Prescott and others around the world are now focussing on. It was thought that Salmonella vaccines would be a suitable vehicle to put these antigens in for the vaccine and after some work, moderate protection from the vaccine given orally was demonstrated.

In the second phase of research, Prescott aimed to evaluate the best possible Salmonella vaccine vectors for use with the C. perfringens antigens. After a number of trials, Prescott identified 6 different salmonella vaccines as good candidates for the C. perfringens antigens, and promising results were obtained in a trial with one of them, when 98% protection against NE was achieved. Unfortunately the research team was never able to replicate that result. However, through DNA tests they discovered that all the antigens they were using had their DNA altered after being cloned into Salmonella, so they focussed on trying to stabilize the Salmonella vaccine in order to express the correct antigens.

Prescott also continued work to understanding the bacterium better and made use of DNA techniques to examine the specific types of C. perfringens involved in causing NE. The research team found that there are two particular strains that cause NE and determined that they were unique in that they contained plasmids with a toxin gene complex capable of causing NE. This was critical information in understanding exactly how C. perfringens causes disease.

The third phase of Prescott’s research in this area was part of the second Poultry Cluster. Work continued on understanding the bacterium and looking for better antigens to use in a vaccine. The output from this work has been shared in a freely available gene databank for the benefit of researchers worldwide trying to solve this problem. Moving away from the use of the Salmonella vaccine as a vehicle for C. perfringens antigens, Prescott started work on developing a live attenuated C. perfringens vaccine. Unfortunately the research team were unable to produce an effective live attenuated oral vaccine based on perfringens itself because it was not capable of triggering an immune response. This information was valuable for showing that this was not an approach to pursue further.

Next steps

Prescott is enjoying the life of retirement. However, he is easing into it as he continues to finish writing all the papers about the NE research. Publications in scientific journals are the main avenue for researchers to learn what has been done on a topic and how best to move forward in solving problems. Overall Prescott’s work on this topic has provided a better understanding of the bacterium and how it causes disease, a better understanding of how the bacterium is put together and how and when it switches its ability to cause disease on or off, a better description and methodology of how to actually investigate all these things, and has helped a great deal in understanding the best models for this infection. Through his work and the work of researchers and collaborators around the world, the understanding of this issue and the technology and techniques to investigate it, have made leaps and bounds in the last 7 years.