Isolation and characterization of two phages infecting Acinetobacter baumannii and their effectiveness in treating BALB/c mice lung infections

Acinetobacter baumannii has raised significant concern due to its high rates of morbidity and mortality, coupled with its increasing resistance to multiple antibiotics including carbapenems. In this current study, two new lytic phages Srynta and Nolivar were isolated from sewage water, characterized in vitro and their therapeutic potential was assessed using a mouse model of pneumonia. In vitro results showed that both phages show efficient adsorption to the propagating host, have good lytic activity, short latent period and high burst size. Sequence analysis showed that Srynta and Nolivar phages have linear dsDNA genomes of 45,218 and 41,230 base pairs with G+C content of 38 mol% and 37.9 mol% and contain 88 and 83 coding sequences, respectively. Transmission electron microscopy showed the icosahedral capsid and contractile tail of the phages and genomic analysis predicted that both phages have myovirus morphology and belong to the class Caudoviricetes. Genomic analysis suggested the therapeutic safety of these phages, as they do not have bacterial virulence factors, antimicrobial resistance genes or lysogenic genes, suggesting that they are potential candidates for phage therapy. The in vivo study demonstrated a high survival rate in the phage cocktail treatment group compared to the control group. Our findings support the potential application of phage therapy as an alternative therapeutic treatment against lung infections caused by carbapenem-resistant A. baumannii .