Improving thermostability of Acinetobacter baumannii phages during cold storage through infecting naïve bacterial hosts.

Despite prior research on optimal temperatures for Acinetobacter baumannii phage storage, thermostability of phages produced from original versus naïve hosts was not addressed. Three A. baumannii phages harvested from three multidrug-resistant A. baumannii strains were used to infect the original hosts and two other naïve strains. For each phage, the quantity of phage production from the three hosts (i.e., one original and two naïve) was compared. The phages produced were stored at two different temperatures (i.e., -20 °C without glycerol and 4 °C) for 24 weeks with the survival probability assessed every two weeks (before 12 weeks of storage) and every four weeks (after 12 weeks of storage). Before cold storage, the lowest production of the three phages was noted in those produced from their original hosts. Consistently, after 24-week storage, significantly lower survival probability was found in phages generated from their respective hosts than those derived from the other two naïve bacterial strains (all p < 0.05). The overall survival of the phages was lower after storage at -20 °C than at 4 °C. In conclusion, the results suggested a benefit of producing phages through infecting naïve bacterial hosts regarding both quantity and storage thermostability that may optimize phage production and storage for clinical application.