The pathogen Vibrio alginolyticus H1 and its antagonist Pseudoalteromonas piscicida H2 associated with the health status of cuttlefish Sepia pharaonis

Abstract

The balance in bacterial community is very important for the maintenance of the health status in the hosts. During the occurrence of a pervasive skin ulcer disease in Sepia pharaonis, bacterial isolate H1 and its antagonist bacterial isolate H2 were simultaneously isolated from the healthy cuttlefish, but only bacterial isolate H1 was isolated from the diseased cuttlefish. In the present study, the genetic and biochemical analysis showed that isolate H1 was identified as Vibrio alginolyticus, and isolate H2 was identified as Pseudoalteromonas piscicida, respectively. The antibiotic susceptibility test using CLSI M45–2015 method showed that the antibiotic resistance of V. alginolyticus H1 and P. piscicida H2 was different, and V. alginolyticus H1 showed strongly resistance to ampicillin. LD50 was calculated based the infection using immerse infection experiment. The result showed that the LD50 for 7 d of V. alginolyticus H1 was 1.58 × 106 CFU/mL, while the no death was observed during the infection of P. piscicida H2. Since the virulence related factors were significantly influenced by host immunity, the virulence factors of pathogen V. alginolyticus H1 was assessed under the stressors of H2O2 and 2,2′-dipyridyl. The results showed that the pathogenicity of V. alginolyticus H1 was associated with the haemolytic activity and bacterial motility. Different components of the P. piscicida H2 were collected and were tested for the antagonistic activity. It was unexpected that no antagonistic substance was detected, while V. alginolyticus H1 showed obvious phobotaxis to P. piscicida H2. It could be concluded that V. alginolyticus H1 was a pathogen of S. pharaonis, and P. piscicida H2 was a potential antagonistic bacteria to inhibit V. alginolyticus H1 via chemotaxis instead of producing antagonistic substance.