2.3. Host range and specificity
The host range of phage pAh6.2TG isolated in this study was conducted on
the collection of 17 A. hydrophila isolates from diseased fish
(Tables 1 and S1). In this study, the Plaque Drop Assay was performed as
described by Adams (1959) with minor modifications. Briefly,
double-layer agar plates containing tested bacterial cells were
prepared. Then, 5 μL of phages (108 PFU/mL) was
dropped on the surface of each plate, kept without moving for 30 min and
incubated at 28 oC for 16 h. Normal saline solution
was used as negative control. Phage susceptibility was indicated by a
clear zone appearing at the location of the drops while no clear zone
indicated unsusceptible host. Specificity test of phage pAh6.2TG to
other common aquatic pathogens (Aeromonas veronii ,Aeromonas schubertii , Edwardsiella ictaluri ,Streptococcus agalactiae ) and probiotic bacteria
(Lactobacillus fermentum , Lactobacillus plantarum ) (Table
1) was done in the same manner. All tests for host range and specificity
were done in triplicates.