Use of bacteriophages (phages) for the treatment of multidrug resistant (MDR) bacterial infections could be a viable alternative or adjunctive to antibiotics [1,2]. However, routine medical implementation of phages is dependent on defining standard guidelines for the preparation of therapeutic products and on the choice of treatment approach (broad application ‘cocktails’ versus tailored phage therapy) [3]. Obligately lytic phages, that specifically kill bacteria immediately upon infection, can be readily isolated from the environment, but the process of selection of candidates for therapeutic use requires a rationalised approach based on unique phage-bacteria (predator-prey) dynamics [4]. We have been investigating rational protocols for the preparation of bacteriophage therapeutics to be used against two globally disseminated pathogenic bacterial clones, E. coli ST131 and K. pneumoniae CG258 [5], along with developing curated bacteriophage libraries for therapeutic use against other important MDR pathogens.
Following a 3-step process, we have: (1) tested the infectivity of >60 phages (from existing collections or de novo isolated from diverse environmental specimens) against fully characterized sets of target bacteria (E. coli ST131 [n=60], K. pneumoniae CG258 [n=20], as well as other MDR E. coli, K. pneumoniae, Staphylococcus ssp. etc.). We have then (2) selected specific phages (n=8 against E. coli ST131; n=12 against K. pneumoniae ST258) for detailed characterisation based on specific in vitro lytic activity, and (3) tested phage combinations (cocktails) with best in vitro synergy in vivo (murine models). We have found that (a) using a combined genomic and molecular microbiology approach is recommended for defining best candidates for therapy; and that (b) phage in vitro activity does not readily directly translate to in vivo efficacy, particularly in the case of phage combinations. Our findings highlight the limitations of the ‘cocktail’ approach for phage applications and may facilitate the process of phage selection for personalised therapy.