Using Bacteriophage To Control Skin Ulceration Syndrome Of The Apostichopus Japonicus Caused By Shewanella Smarisflavi

Sea cucumber has become the most costly food in China due to its rich nutritional value and medicinal value. The annual output has already been up to 30 billion RMB in China. With the deepen development of culture technology, the cost has been reduced, but the possibility of the bacterial diseases outbreak has been increased, resulting in substantial economic losses of aquaculture in China. However, the emergence of resistant strains made antibiotics no more an efficient way for treatment. Therefore, a perfect alternative for antibiotics become the urgent problem remained to be solved.A Shewanella marisflavi phage was screened using double-plate method from the sewage of an aquatic product wholesale market and been named as PSM-1. The biological characteristics of PSM-1 were studied. Morphological analysis revealed that the phage belongs to the Myoviridae family. Phage PSM-1 showed insensitive to chloroform, host specificity and a very rapid adsorption to its host cells during the first 8 minutes. One-step growth curve analysis of PSM-1 revealed that the latent periods were 20 min, and the rise periods were 40 min, with a burst size of about 219 PFU per infected cell. The stability test proved that the lytic activity was optimal under the condition of 28 ?, pH 7.0.Phage PSM-1 was delivered by intraperitoneal injection and immersion in therapy experiments. The administration of PSM-1 protected sea cucumbers was assessed through comparing the survival rate among negative group, positive group and phage treatment with different dose and delivery time. Intraperitoneal injection group and immersion could improve survival rate from 0% to more than 80% and more than 60% respectively. The optimal time of administration was from 1 day before infection to 2 days after infection and 2 days before infection to 1 day after infection respectively. It is worth of mentioning that both intraperitoneal injection and immersion could improve survival to more than 90% with suitable dose and administration time.The influence of phage on sea cucumber's immune response was evaluated. The administration way of the highest survival rate group was adopted through comparing with blank group and negative group, studied the change of SOD, NOS, POD, AKP and ACP in sea cucumber's coelomic fluid. The result presented that the phage had imposed a significant effect on the change of sea cucumber body's immune factors, which may be possibly caused by limitation of pathogen's growth.To conclude, phage PSM-1 was obtained when a major causative agent of skin ulceration syndrome in sea cucumbers Shewanella marisflavi was taken as hosts. The biological characteristics and protection effect of PSM-1 were researched. The result showed that phage PSM-1 could increase the survival rate of sea cucumber by adopting intraperitoneal injection and immersion. Besides, the changes of immune factors in sea cucumbers were also evaluated. These data have provided a scientific reference and evidence for the further researches on phage therapy.