Increasing antimicrobial resistance in Acinetobacter baumannii has resulted in limited to no treatment options. Bacteriophage therapy promises to assist in filling this treatment void. Six related phages (AB1I1L, AB1I1M, AB1I1P, AB1I1T, AB2I2, AB2I3) that target A. baumannii were isolated from wastewater and possessed an icosahedral structure and contractile tail consistent with myoviridae. Purified phage of high quality and low endotoxin levels (< 0.5EU/mL) demonstrated rapid adsorption and potent lysis. Encouragingly 18/40 (45%) tested clinical isolates were susceptible to one or more members of this phage species, including 11 of 27 (41%) carbapenem resistant A. baumannii isolates. Importantly, pools of phage tolerant/resistant A. baumannii that developed after exposure to each of the six phages were highly susceptible to human ascites mediated bactericidal activity ex vivo. An unusual and potentially important feature of this phage species is that the bacterial capsule is not their receptor; in fact, capsule impedes phage activity. Whole genome sequencing did not identify bacterial virulence or resistance genes or phage lysogenic genes. Taken together, these phages are potential candidates for phage therapy and warrant additional preclinical evaluation as a treatment modality for XDR-A. baumannnii.
