Aeromonas hydrophila is a zoonotic pathogen and an important fish pathogen. A new lytic phage, Ahy-yong1, against multi-antibiotic-resistant pathogen A. hydrophila was isolated, identified, and tentatively used in therapy. Ahy-yong1 possesses a head of approximately 66 nm in diameter and a short tail of approximately 26 nm in length and 32 nm in width. Its complete dsDNA genome is 43,374 bp with a G + C content of 59.4%, containing 52 predicted opening reading frames (ORFs). Taxonomic analysis indicated Ahy-yong1 as a new species of the Ahphunavirus genus of the Autographiviridae family of the Caudoviricetes class. Ahy-yong1 was active only against its indicator host strain among the 35 strains tested. It is stable at 30–40 °C and at pH 2–12. Aeromonas phage Ahy-yong1 revealed an effective biofilm removal capacity and an obvious protective effect in brocade carp (Cyprinus aka Koi). The average cumulative mortality for the brocade carp in the blank groups intraperitoneally injected with PBS was 1.7% ± 2.4%;for the control groups treated with A. hydrophila (108 CFU/fish) via intraperitoneal injection, it was 100.00%;and for the test group I, successively treated with A. hydrophila (108 CFU/fish) and Aeromonas phage Ahy-yong1 (107 PFU/fish) via intraperitoneal injection witha time interval of 2 hours, it was only 43.4% ± 4.7%. Furthermore, the cumulative mortality of the test group II, successively treated with Aeromonas phage Ahy-yong1 (107 PFU/fish) and A. hydrophila (108 CFU/fish), was only 20.0% ± 8.2%, and that of the test group III, simultaneously treated with Aeromonas phage Ahy-yong1 (107 PFU/fish) and A. hydrophila (108 CFU/fish), was only 30.0% ± 8.2%. The results demonstrated that phage Ahy-yong1 was very effective in the therapies against A. hydrophila A18, prophylaxis was more effective than rescue, and earlier treatment was better for the reduction of mortality. This study enriches knowledge about Aeromonas phages.

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Both live and dead Salmonella typhimurium (S.T) are harmful to human health, but there are differences in pathological mechanism, dosage, and security. It is crucial to develop a rapid and simultaneous assay to distinguish and quantify live and dead S.T in foods. Herein, one dual-mode biosensor for simultaneous detection of live and dead S.T was fabricated based on two phage probes, using portable bioluminescence and fluorescent meter as detectors, respectively. Firstly, a magnetic phage capture probe (M-P1) and a phage signal tag (P2-S) labeled with SYTO 13 fluorescent dye were prepared, respectively. Both M-P1 and P2-S can specifically conjugate with S.T to form a magnetic sandwich complex. After magnetic separation, the isolated complex can emit a fluorescent signal under an excited 365 nm laser, which can reflect the total amount of S.T. Afterwards, the lysozyme was added to decompose the captured live S.T, which can release ATP and produce a bioluminescent signal corresponding to the live S.T amount. The dead S.T concentration can be deduced by the difference between total and live examples. The detection limit of 55 CFU/mL for total S.T and 9 CFU/mL for live ones was within 20 min. The assay was successfully employed in milk samples and prospectively for on-site screening of other dead and live bacteria, while changing the phages for the targets.

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