Evaluating antimicrobial peptides for animal pathogens and forecasting resistance
- Project No: 2022F142R
- Lead Researcher(s): Antonio Ruzzini (University of Saskatchewan)
- Collaborators: Kathyana Deeyagahage (PhD. Student); Jenny Liang (Research Technician)
- Year Started: 2022
- Year Completed: 2025
Background
The last new class of antibiotics was discovered in 1987. While new antibiotics have been commercialized and sold for both humans and livestock, for over 30 years, these new antibiotics have just been variations of the same drug. For example, both Draxxin and Zuprevo belong to the macrolide class of antibiotics. This is important because bacteria tend to develop resistance to a class of antibiotics – in the example above, bacteria that develop resistance to Draxxin are often also resistant to Zuprevo. So while antibiotics are effective tools against Bovine Respiratory Disease (BRD), concerns about antibiotic resistance means that other options need to be explored.
Antimicrobial peptides (AMPs) are tiny protein fragments that are found in the immune systems of most animals and can have a wide range of antimicrobial effects on bacteria and other pathogens. They have been proposed as alternatives to current antibiotics. Previous work led to the discovery of a set of broad-spectrum AMPs, that may be able to be altered to have a specific targeted effect on certain bacterial pathogens. Resistance to AMPs may also develop more slowly because they can act on multiple cellular targets at once. The trade-off is that AMPs are often active at higher concentrations and their activity is less specific, meaning that they might accidentally harm unintended targets.
Objectives
The objectives of this study were to:
- Optimize AMPs to specifically target and kill Mannheimia haemoloytica
- Predict potential targets for drug development
- Examine the potential development of antimicrobial resistance to AMPs
What they did
The family of AMPs studied was called staphyloccocal toxin-inspired peptides (STIP). The research team made a series of modifications to these STIPs in order to improve activity specifically against Mannheimia haemolytica (MH) while attempting to avoid unintended consequences. 60 STIPs were screened against MH and other bacteria that are generally more sensitive to AMPs. They then investigated a few of these STIPs in more detail.
What they learned
The screening revealed that maintaining positively charged amino acids at the start of the AMP sequence was key to killing MH. Thirteen STIPs were found to be 2-15 fold more selective for MH; however, increased selectivity was also often matched to increased death of unintended cells. They were able to identify four particular STIPs that were both selective for MH but also reduced undesirable cell death compared to other STIPs.
They then zeroed in on three individual STIPs to better understand how they worked to kill MH. They also looked at activity against Staphyloccocus aureus (SA), a representative Gram positive bacteria (MH is Gram negative), to determine whether lethality mechanisms were similar or different between these types of bacteria. For SA, the STIPs worked by disrupting the cell membrane, thus resistance to the STIPs could be developed when the bacteria were able to change their cell membrane (a common resistance mechanism). For MH, the team was unable to discover a mechanism of resistance to the STIPs.
They also learned that STIPs are quite complex, and minimal differences in STIP structure could cause large changes in how they are able to disrupt bacterial targets.
What they learned
While this project is early stage, lab-based research, it revealed some promising avenues for further study of STIPs (and other AMPs). Particularly, that there are STIPs that a) have the ability to destroy pathogens of interest to the beef sector like MH, b) have selectivity for that specific pathogen without concurrently increasing the death of other cells, and it provided more insight into STIP mode of action, means that at some point they may become viable alternatives to antibiotics.
Future work will need to occur to further characterize these STIPs, examine their ability to reduce disease in live animals, and eventually develop them for commercialization – assuming that continued research in this area continues to show positive results.
This project was also supported by RDAR and a MITACS Gloablink Resesearch Internship
