Evaluating the effectiveness of Streptococcus parauberis bacteriophage Str-PAP-1 as an environmentally friendly alternative to antibiotics for aquaculture

A new bacteriophage, Str-PAP-1, which infects Streptococcus parauberis, was isolated and characterized. Str-PAP-1, classified as a member of the family Siphoviridae, has a double-stranded DNA genome with 35.3% GC content and 36,595 base pairs containing putative open reading frames. A BLAST search revealed that bacteriophage Str-PAP-1 bears no similarity to any previously reported bacteriophages. In a susceptibility test, 35 of the 55 (63.6%) S. parauberis field isolates tested, which were collected from streptococcosis-afflicted olive flounder (Paralichthys olivaceus) from the year 2010 to 2013 in Jeju-do province, Korea, were susceptible to the bacteriophage Str-PAP-1. This suggests that the bacteriophage Str-PAP-1 can be used to treat or prevent streptococcosis caused by S. parauberis. In addition, the effects of dietary supplementation with bacteriophage Str-PAP-1 at varying doses (T1: 1×105pfu/g, T2: 1.5×105pfu/g and T3: 2×105pfu/g) on fish growth performance, the incidence of S. parauberis infections, and fish mortality, were evaluated. Feeding fish with the bacteriophage Str-PAP-1 improved growth (length: 9.3%, 5.4%, and 9.7%; weight: 27.1%, 21.2%, and 27.5% by T1, T2, and T3 doses, respectively), and reduced both the detection rate of S. parauberis and mortality (relative percent survival (RPS): 52.3%, 51.6%, and 53.1%, respectively) in all test groups. Thus, bacteriophage Str-PAP-1 is an environmentally friendly agent that can prevent and treat streptococcosis caused by S. parauberis.