Formation of therapeutic phage cocktail and endolysin to highly multi-drug resistant Acinetobacter baumannii: in vitro and in vivo study

Objective(s): Phage therapy is a potential alternative treatment for infections caused by Acinetobacter baumannii, a significant nosocomial pathogen, which has evolved resistance to almost all conventional antimicrobial drugs in poor hygiene and conflicts areas such as Iraq. Materials and Methods: Bacteriophages were isolated to highly resistant isolates of A. baumannii to form therapeutic phage cocktail, and to extract and evaluate native endolysin activity. Bacterial samples were collected in Al-Imamein Al-kadhimein Medical City Hospital. Phages were isolated from different regions in Baghdad city including (soil, sewage, irrigation channels). Phage endolysin was extracted from highly lytic phages that produced halo-like appearance around inhibition zone. Results: Up to 23 isolates of extensive- and pan- drug resistant (XDR, PDR) A. baumannii were isolated from patients with various infections, and 136 lytic phages specific to A. baumannii were isolated. Each bacterial isolate was sensitive to at least one lytic phage. Accordingly, a phage cocktail was formulated which remarkably minimized bacterial resistance to lysis by phages when compared to individual lytic phages. And, the phage cocktail succeeded in treating and saving life of all bacteremic mice with A. baumannii versus the non-treated group. In addition, the endolysin native activity to A. baumannii was evaluated in this study; endolysin revealed a potent antibacterial activity (> 1 log) reduction of bacterial density in just one hour of endolysin treatment. Conclusion: The phage therapy assessed in this study showed an ability to efficiently solve the problems of “superbug” bacteria by lysing effectively most XDR, PDR bacteria in vitro and in vivo. And, phage cocktail was shown to be superior over single-phage preparations in treating A. baumannii with much less resistance rate to therapeutic phages. Furthermore, intrinsic activity of native endolysin revealed promising results to tackling superbug pathogens.