Antibiotics and phages - a contradiction?
No. Both have the same aim, to kill or reduce unwanted bacteria, both are often applied together. However, the decision whether or not and how to apply both therapeutic strategies depends on numerous factors and will always remain the decision by the physician and cannot be generalized here.
The therapeutic effect of successful antibiotic treatment can be compared with successful phage therapy. The therapeutic aim is achieved when the pathogenic bacterium, this means the individual patient’s strain, is diminished. In both cases of therapy, single resistant bacterial cells might appear or definitely, they usually occur, often to an unpredictable extent. But, while antibiotic resistances will be transferred to the next bacterial generation “vertically” or to other bacteria by “horizontal” gene transfer and present a risk for future antibiotic therapies, phage therapy has a completely different principle: suitable phages which are purified and ready to be tested are screened in the single case to identify a cocktail of few optimally or synergistically acting phages. This means phage therapy offers the option to be much more individualized and to leave the patient’s microbial community of the microbiome unaffected. Whereas the number of available antibiotic market products is limited, the number of potential phages is principally unlimited as phages are abundant in natural habitats. So, bacterial resistance against phages is not a sustainable problem. Because of high phage-host specificity, phages have to be screened against the patient’s pathogen in a phagogram before use to ensure efficacy. Broad-spectrum phages that cover a high number of strains of a bacterial species are rare so that use of phage cocktails is current practice. Ideally, a patient pathogen would be tested in parallel in an antibiogram and phagogram.
Important:
Bacterial antibiotic resistances have sustainable negative effects, resistances remain persisting, are transferred between bacteria and distributed in the environment but also in the patients’ microbiomes. Bacterial resistances against phages play an unimportant role for the environment and the microbiota and phage mixtures (cocktails) are applied to avoid resistance against single phages. Running clinical research projects aiming at the development of licensed fixed phage cocktails will have to demonstrate their efficacy potential on broad basis. Studies have shown that applying both, antibiotics and phages, at the same time or successively, may often have a synergistic effect, thus one strategy does not exclude the other.