## 3 Intestinal Bacteriophages and Faecal Virome Transplants
### Advantages and Potential Benefits of Facal Virome Transplants
This perspective can be compared to the usage of the already-mentioned artificially defined bacterial formulations, but the amount of biomass that has to be introduced could potentially be lower in FVT procedures. On top of this, novel state-of-the-art approaches can significantly enhance the bactericidal effect of phages through genetic modification based on integrating a CRISPR-Cas system into their genome [97]. While such solutions seem to resemble targeted phage therapy more than typical FVT, they remain a fascinating approach that should not be overlooked. Phages can be administered in suspension directly into the alimentary tract [95] or immobilised in many different mediums that are fine-tuned to achieve desired results, as can be seen in studies focused on immobilising specific phage species. The usage of liposome particles is an effective way of securing the passage of bacteriophages through the acidic and protease-rich contents of the stomach [98], although liposomes can also be utilised to increase the retention time and viability of bacteriophage preparations used topically for wound treatment [99]. Phages can also be freeze- or spray-dried and then encapsulated [100; 101] to obtain products that can be stored for months in nonrefrigerated conditions with a relatively low decrease in viral viability levels. For now, there are no studies that have focused on utilising such techniques to immobilise an entire intestinal phageome of a donor, and the physicochemical qualities of individual viruses--such as their size, charge, and presence or absence of a lipid envelope--would definitely pose a challenge in devising a suitable method that maximises both the practicality and viability of the resulting preparation. Yet long shelf-life in easy-to-achieve storage conditions is a prominent advantage of phage preparations, one that is especially noticeable when compared with the shelf-life of spray-dried preparations of Gram-negative bacteria kept in nonrefrigerated environments, which rarely exceed a few weeks [102]. This may have specific implications for future ways of regulating _Bacteroidota_ populations in the gut, as even though _Bacteroides_-based probiotics are currently being developed [103], the production and storage of such preparations will probably require overcoming the same challenges encountered when processing other Gram-negative microorganisms. If these challenges are not resolved in a way that allows for logistically sound storage and distribution of bacterial preparations, then perhaps phages could prove to be a viable and scalable alternative. Moreover, when considering FVT approaches, it is vital to note that bacteriophages can directly affect not only bacteria but the host itself. Surprisingly, bacteriophages are actually able to penetrate the intestinal epithelium using a variety of mechanisms and then directly and indirectly influence the cells of the immune system [104]. A paper by [PERSON] al. [105] provided several examples of bacteriophages decreasing elevated cytokine levels, both in vitro and in vivo, and described their ability to affect leukocytes in gut-associated lymphoid tissue. Some of these interactions may not necessarily be beneficial, as there are also reports of bacteriophages inciting immune responses rather than quenching them [106]. However, future research will hopefully elucidate the interactions between bacteriophages and the host immune system to help create efficient therapies that holistically integrate direct antipathogen action with desirable forms of immunomododulation.