1. Investigación

Bacteriophages selectively infect and kill their target bacterial host, being a promising approach to controlling zoonotic bacteria in poultry production. To ensure confidence in its use, fundamental questions of safety and toxicity monitoring of phage therapy should be raised. Due to its high specificity, a minimal impact on the gut ecology is expected; however, more in-depth research into key parameters that influence the success of phage interventions has been needed to reach a consensus on the impact of bacteriophage therapy in the gut. In this context, this study aimed to investigate the interaction of phages with animals; more specifically, we compared the caecum microbiome and metabolome after a Salmonella phage challenge in Salmonella-free broilers, evaluating the role of the phage administration route. To this end, we employed 45 caecum content samples from a previous study where Salmonella phages were administered via drinking water or feed for 24 h from 4, 5 to 6-weeks-old broilers. High-throughput 16S rRNA gene sequencing showed a high level of similarity (beta diversity) but revealed a significant change in alpha diversity between broilers with Salmonella-phage administered in the drinking water and control. Our results showed that the phages affected only a few genera of the microbiota’s structure, regardless of the administration route. Among these, we found a significant increase in Streptococcus and Sellimonas in the drinking water and Lactobacillus, Anaeroplasma and Clostridia_vadinBB60_group in the feed. Nevertheless, the LC-HRMS-based metabolomics analyses revealed that despite few genera were significantly affected, a substantial number of metabolites, especially in the phage administered in the drinking water were significantly altered (64 and 14 in the drinking water and feed groups, respectively). Overall, our study shows that preventive therapy with bacteriophages minimally alters the caecal microbiota but significantly impacts their metabolites, regardless of the route of administration.

Bacteriophage therapy is being considered as a promising tool to control Salmonella in poultry. Nevertheless, changes in gastrointestinal tract environmental conditions throughout the production cycle could compromise the efficacy of phages administered orally. The main objectives of this study were to assess the optimal timing of the phage administration over a 42-day production cycle and to compare microencapsulated and non-encapsulated phages and the spatial and temporal dynamics of the phage delivery along the gastrointestinal tract. Phage FGS011 was encapsulated in the pH-responsive polymer Eudragit® L100 using the process of spray drying. At different weeks of the chicken rearing period, 15 broilers were divided into three groups. Over a period of 24 h, group 1 received non-encapsulated phages (delivered through drinking water), group 2 received microencapsulated phages (incorporated in animal feed), and group 3 did not receive any phages. Microencapsulation was shown to enable efficient delivery of the bacteriophages to the animal gut and cecum throughout the animal rearing period. During the six weeks of application, the crop displayed the highest phage concentration for both phage delivery methods. The L100 based encapsulation offered significant protection to the phages from the harsh environmental conditions in the PV-Gizzard (not seen with phages administered in drinking water) which may help in the delivery of high phage doses to the cecum. Future Salmonella challenge studies are necessary to demonstrate the benefits of microencapsulation of phages using L100 formulation on phage therapy in field studies during the rearing period.

The therapeutic use of bacteriophages is recognized as a viable method to control Salmonella. Microencapsulation of phages in oral dosage forms may protect phages from inherent challenges of the gastrointestinal tract in chickens. Therefore, the main objective of this study was to assess the survival of Salmonella BP FGS011 (non-encapsulated and microencapsulated) through the gastrointestinal tract under in vitro as well as in vivo conditions after oral administration to 1-day-old chicks. To this end, the phage FGS011 was encapsulated in two different pH-responsive formulations with polymers Eudragit® L100, and Eudragit® S100 using the process of spray drying. Phages encapsulated in either of the two formulations were able to survive exposure to the proventriculus-gizzard in vitro conditions whereas free phages did not. Moreover, phages formulated in polymer Eudragit® S100 would be better suited to deliver phage to the caeca in chickens. In the in vivo assay, no statistically significant differences were observed in the phage concentrations across the gastrointestinal tract for either the free phage or the encapsulated phage given to chicks. This suggested that the pH of the proventriculus/gizzard in young chicks is not sufficiently acidic to cause differential phage titre reductions, thereby allowing free phage survival in vivo.