In Vitro Design and Evaluation of Phage Cocktails Against Aeromonas salmonicida

Abstract

As an alternative approach against multidrug-resistant bacterial infections, phages are now being increasingly investigated as effective therapeutic agents. Here, aiming to design an efficient phage cocktail against Aeromonas salmonicida infections, we isolated and characterized five lytic A. salmonicida phages, AS-szw, AS-yj, AS-zj, AS-sw, and AS-gz. The results of morphological and genomic analysis suggested that all these phages are affiliated to the T4virus genus of the Caudovirales order. Their heterogeneous lytic capacities against A. salmonicida strains were demonstrated by experiments. A series of phage cocktails were prepared and investigated in vitro. We observed that the cocktail combining AS-gz and AS-yj showed significantly higher antimicrobial activity than other cocktails and individual phages. Given the divergent genomes between the phages AS-yj and AS-gz, our results highlight that the heterogeneous mechanisms that phages use to infect their hosts likely lead to phage synergy in killing the host. Conclusively, our study described a strategy to develop an effective and promising phage cocktail as a therapeutic agent to combat A. salmonicida infections, and thereby to control the outbreak of relevant fish diseases. Our study suggests that in vitro investigations into phages are prerequisite to obtain satisfying phage cocktails prior to application in practice.

Isolation, Characterization, and Application of a Bacteriophage Infecting the Fish Pathogen Aeromonas hydrophila

“…Moreover, the slow growth of phage-resistant strains has been observed, which can limit the bacterial population to a level controllable by the host immune system [27,32]. One possible method to overcome the presence or occurrence of phage-resistant strains is the application of a phage cocktail rather than a single phage isolate, as shown by Chen et al [33]. Although we isolated only two phages that can infect A. hydrophila from seawater, isolation of more A. hydrophila phages is promising, as shown by Hassan et al [34], and further isolation, characterization, and application of A. hydrophila phages are necessary.…”

Isolation and Characterization of Multidrug Resistance Aeromonas salmonicida subsp. salmonicida and Its Infecting Novel Phage ASP-1 from Goldfish (Carassius auratus)

“…Similar observation has reported by Kim et al [17] for phage PAS 1 against an Aeromonas salmonicida strain, that bacterial resistance had shown after 3, 6, and 24 h at MOIs of 10, 1, and 0.1, respectively. As suggested by several researches, developing a cocktail combining two or multiple different phages would be an effective solution to overcome the development of ASP-1 phage-resistant bacterial mutants and broaden the host range [19,48,49].…”

“…Phages infecting Aeromonadaceae have been isolated and characterized from different environments [16][17][18][19][20]. Reports demonstrated that phage efficacy could vary with type and effectiveness of the bacterial disease and the fish species.…”

Complete Genome Sequence of Aeromonas Phage ZPAH7 with Halo Zones, Isolated in China

“…Then, phage activity in the supernatant was detected with the spot assay. This phage was a novel lytic phage with large plaques (3.5 ± 0.2 mm) compared with those of other phages (0.38 to 1.6 mm) (1, 5) and with halo formation (a lightening zone of 10.5 ± 0.5 mm). Halo formation has been linked to exopolysaccharide depolymerization and biofilm degradation (6, 7).…”