Summary
The emergence and rapid spread of multidrug‐resistant bacteria has induced intense research for novel therapeutic approaches. In this study, the Acinetobacter baumannii bacteriophage D2 (vB_AbaP_D2) was isolated, characterized and sequenced. The endolysin of bacteriophage D2, namely Abtn‐4, contains an amphipathic helix and was found to have activity against multidrug‐resistant Gram‐negative strains. By more than 3 log units, A. baumannii were killed by Abtn‐4 (5 µM) in 2 h. In absence of outer membrane permeabilizers, Abtn‐4 exhibited broad antimicrobial activity against several Gram‐positive and Gram‐negative bacteria, such as Staphylococcus aureus, Pseudomonas aeruginosa, Klebsiella pneumonia, Enterococcus and Salmonella. Furthermore, Abtn‐4 had the ability to reduce biofilm formation. Interestingly, Abtn‐4 showed antimicrobial activity against phage‐resistant bacterial mutants. Based on these results, endolysin Abtn‐4 may be a promising candidate therapeutic agent for multidrug‐resistant bacterial infections.
In recent years, turbot (Scophthalmus maximus L.) ascites caused by Edwardsiella tarda has occurred frequently in China, causing serious economic losses. In this study, with E. tarda ET9 as the host bacteria, a lytic phage was isolated and named vB_EtaM_ET-ABTNL-9 (referred to as PETp9). The effect of using phage to prevent and control E. tarda infection in turbot was discussed. The results showed that the best preventive effect was achieved after 7 days of feeding phage with multiplicity of infection (MOI) = 10 in the phage-feeding experiment; in the phage-injection therapy, treatment was most effective when the phage with MOI = 10 was injected intraperitoneally immediately after the challenge; in the phage-immersion therapy, the best therapeutic effect was obtained when the infected turbot were immersed in phage-seawater mixture (MOI = 10) for 3 h. During the experimental period, the activities of non-specific immune-related enzymes in the blood of turbot were significantly increased in the untreated group, while that of the phage treated group showed a downward trend and gradually reached normal levels. It was also observed that a certain concentration of phages was present in both turbot cultured water and the intestinal tract during the experiment. Therefore, phage may be another effective control agent against E. tarda infection in turbot culture.
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