Potential uses of bacteriophages for microbial meat safety

Why bacteriophages?

Antimicrobial resistance (AMR) poses a major threat to global health. It is widely known that the main contributor to AMR is the overuse of antimicrobials. Primarily their use in human medicine, but also increasing recognition of their continued use in livestock, has facilitated the selection and spread of AMR bacteria throughout the food chain.¹ Consequently, despite antimicrobials being crucial for treating bacterial infections, current regulations aim at reducing their use in livestock.

Additionally, the consumption of contaminated products of animal origin, mainly undercooked poultry meat and eggs, is considered the main source of Campylobacter and Salmonella, the most common foodborne pathogens causing zoonotic illnesses in humans. Shiga toxin-producing E. coli (STEC) and enterohemorrhagic E. coli (EHEC; O157:H7) are also well-known foodborne pathogens related to the meat sector, with cattle being the main harbourers of zoonotic strains. These bacteria can contaminate food products at any point in the food chain, by direct contact with animals (eg, during slaughter or carcass processing, by direct faecal contamination) or indirectly by vectors, and contribute significantly to hospitalisations and deaths worldwide, despite the advances in pathogen management. Traditional food preservatives and food processing methods (including pasteurisation, high pressure, ultraviolet (UV) or chemical treatments) can reduce pathogens in foods in different levels. However, these methods may also adversely affect the organoleptic properties and/or nutritional value and eliminate the beneficial microbes in foods.

Thus, the development of innovative and effective alternatives to controlling bacterial infections has become an urgent issue, and additional strategies must be implemented to enhance animal health and welfare and promote the responsible use of antimicrobials for a safer food chain. One of the most promising approaches uses bacteriophages (phages), viruses that infect bacteria, which have demonstrated potent antimicrobial activity against most foodborne pathogens.²

The main advantages of these microorganisms can be summarised as follows:

• Natural origin: Phages are the most abundant microorganisms in the world and are naturally present in the microbiome of soils, water, gut and in foods, which makes them generally safe for other organisms such as animals, humans and plants, as well as the environment³
• High specificity: Phages are highly specific for selected bacteria, which enhances the safety of commensal and symbiotic microbiota and other beneficial microorganisms and allows the development of personalised therapies
• Versatility: The use of phages also relies on their self-replication, self-limitation, ease of handling, and low cost of production, allowing them to be applied at every stage of the farm-to-fork continuum,^2,4 eg, for veterinary use in animal production, disinfection of equipment and contact surfaces on farms and in food production/preparation, or direct use in fresh meats and meat products as natural preservatives. Also, they can be used together with other bacteriophages and/or protective cultures to boost their antibacterial efficiency.

Combined, these unique characteristics make bacteriophages the most reliable alternative for effectively inhibiting pathogenic bacteria and reducing zoonotic and foodborne diseases. In fact, in Europe, where their use is not specifically regulated, one of our recent studies revealed that 90 percent of producers and 85 percent of consumers were disposed to accept bacteriophages as a standard biocontrol measure in food production and processing.⁵ Accordingly, the number of commercial phage-based products approved for use in animal breeding and food safety is constantly increasing in many countries. The following focuses on providing introductory highlights related to the use of phages as biocontrol and food (meat) safety agents.

Pathogen control in animal production and food industry

Numerous studies have reported the use of phages to prevent and treat diseases caused by Campylobacter, Salmonella or E. coli, among others, in animals for food production. Most of the studies showed phage biocontrol success against these three pathogens, leading to significant protection against infections (prophylactic use), decreased levels of pathogenic bacteria in tissues and a reduction of the associated mortality and morbidity of the animals,⁶ showing that phages are a promising and effective alternative to antibiotics.

Antimicrobial resistance: It hasn’t gone away

Apart from animal health protection, similarly, statistically significant differences in Salmonella or Campylobacter reduction after phage treatments demonstrated that their application at late stages of animal growth may also be a promising measure for the control of this bacteria in subsequent stages of the food production chain. For instance, reducing the Campylobacter load in broiler chicken intestines by three logs prior to slaughter has been estimated to reduce the risk of human campylobacteriosis attributable to the consumption of poultry meat by 58 percent.⁷ In this sense, at least one trial has demonstrated that two different phages against Campylobacter jejuni in successive application are able to achieve this goal with no collateral effects on the gut microbiota.⁶

Phage biocontrol has also shown great potential to be used as a safety control approach at the stages of food production, distribution and consumption, by direct application to foods as a bio-preservative. Although no solution should replace good hygiene practices and control measures in food production, phages may help to reduce microbial counts by one to three logs or prevent microbial growth during shelf-life, without affecting the remaining microbiota or the organoleptic properties of fresh meat.⁸ Adopting phage use in hurdle-based approaches together with non-thermal technologies or packaging (eg, phages and modified atmosphere packaging or high hydrostatic pressure) could also enhance the final outcome.

Apart from numerous scientific reports, several commercial products are already available and have been proved for effective biocontrol of foodborne pathogens in meat products, fresh meat (poultry, turkey, beef), pet foods and other foods (fish, vegetables, dairy).^4,6 Furthermore, the application of certain phages could also provide an innovative alternative for surfaces disinfecting and to reduce biofilms on food-contact surfaces.

Challenges: are phages the ultimate solution?

As mentioned, the available commercial products and the results of the published studies indicates that phages are already a valid choice for biocontrol of pathogens. Nevertheless, optimal effectiveness and stability of phages requires individual optimisation of numerous factors for animals and foodstuffs, such as phage administration timing (prophylactic vs. therapeutic), application route, number of phages used (single vs. cocktail), the food matrix or storage temperature, as well as environmental factors.⁹ Finally, any phage application must follow relevant regulations. Accordingly, the approval of any phage-based solution requires deep research and investment, like other therapeutic products or food additives, with the purpose of accurately characterising and selecting the most competent phages for each application, as well as demonstrating effectiveness and safety, and overcoming pending gaps and challenges that could limit their use.

References

1. Booton RD, et al. (2021). One Health drivers of antibacterial resistance: Quantifying the relative impacts of human, animal and environmental use and transmission. One Health, 12, 100220. https://doi.org/10.1016/j.onehlt.2021.100220
2. Endersen L, Coffey A. (2020). The use of bacteriophages for food safety. Current Opinion in Food Science, 36, 1–8. https://doi.org/10.1016/J.COFS.2020.10.006.
3. Dec M, et al. (2020). Efficacy of experimental phage therapies in livestock. Animal Health Research Reviews, 21(1), 69–83. https://doi.org/10.1017/S1466252319000161
4. Lavilla M, et al. (2023). Natural Killers: Opportunities and Challenges for the Use of Bacteriophages in Microbial Food Safety from the One Health Perspective. Foods12, 552. https://doi.org/10.3390/foods12030552
5. AZTI (2021). Consumers and producers in favour of using phages as an alternative to antibiotics in the fight against Campylobacter in poultry. Available online at https://www.azti.es/en/consumers-and-producers-in-favour-of-using-phages-as-an-alternative-to-antibiotics-in-the-fight-against-campylobacter-in-poultry/  
6. Alomari MMM, et al. (2021). Bacteriophages as an alternative method for control of zoonotic and foodborne pathogens. Viruses, 13(12), 2348. https://doi.org/10.3390/V13122348
7. EFSA BIOHAZ Panel (2020). Update and review of control options for Campylobacter in broilers at primary production. EFSA Journal, 2020, 18, 6090. https://doi.org/10.2903/j.efsa.2020.6090.
8. Atterbury RJ. (2009). Bacteriophage biocontrol in animals and meat products. Microbial Biotechnology (2009) 2(6), 601–612. https://doi.org/10.1111/j.1751-7915.2009.00089.x
9. (2009). The use and mode of action of bacteriophages in food production. EFSA Journal, 7(5), 1–26. https://doi.org/10.2903/J.EFSA.2009.1076