Phages are naturally-occurring bacterial viruses which infect specific species or strains of bacteria. There are 2 general types of phages, lytic and lysogenic.
Lytic phages infect host bacteria through a process involving attachment of the phage to the bacterium; insertion of the phage genome into the host cell; cessation in the synthesis of host components; host mediated replication of phage components including capsid proteins and nucleic acids; assembly of new phage particles; lysis of the host; and release of progeny phages.
insertion 삽입
cessation 중단
synthesis 합성
components 부품
mediate 중재하다
replication 복제
Since lytic phages replicate quickly and rapidly cause death and lysis of the host, they are ideal for the development of phage therapies for use in treating animal infections and in reducing pathogens in various foods and the environment.
replicate 복제하다
therapy 치료
In contrast, lysogenic phages may replicate in a manner similar to that of the lytic phages, but can also integrate their DNA into the host’s chromosomes, a process referred to as lysogenization.
integrate 통합시키다
chromosomes 염색체
lysogenization 용원화
The lysogenized host cells may replicate normally for generations, however, at some point they may spontaneously or through induction by chemicals, radiation, carcinogens, etc. excise the phage DNA, and synthesize new phage particles, which in turn lyse the host, releasing more lysogenic viruses into the surrounding medium.
replicate 자기 복제를 하다
normally 보통
spontaneously 자연스럽게
This process of phage DNA integration into the host genome can enhance the virulence of the host, as in the case of a Myoviridae integrating into Vibrio parahaemolyticus,10 or a myovirus-like phage integrating into Vibrio harveyi,11-13 or the filamentous phage CTXɸ integrating into Vibrio cholerae and Vibrio mimicus.
integration 통합
virulence 독성
In addition, during the excision of the phage DNA from the host chromosome, host DNA may become incorporated into the phage DNA. Thus, lysogenic phages can facilitate the horizontal transfer of bacterial genes from one bacterium to another to enhance bacterial virulence.
excision 삭제
incorporate 포함하다
facilitate 가능하게 하다
Horizontal gene transfer enables bacteria to respond and adapt to their environment much more rapidly by acquiring large DNA sequences from another bacterium in a single transfer
For these reasons, lysogenic phages should never be used in phage therapy. Advances in whole genome sequencing of phages are facilitating the identification of genetic components involved in lysogeny to ward off the use of lysogenic phages in commercial applications.
phage therapy 파지치료
Lytic phages, on the other hand, do not integrate into the host’s DNA and do not enhance the host’s virulence, making them ideal candidates for therapeutic use. Phages have been used for decades to effectively treat human wound and gastrointestinal infections in Eastern Europe and countries of the former Soviet Union.
Phages are now commercially available for: treating bacterial diseases in humans, animals, and agricultural crops; reducing pathogens to enhance food safety; and for aquaculture (reviewed in Housby and Mann,18 Hodgson,19 and Ly-Chatain20). Only one company, Phage Biotech Ltd. in Israel, was listed as developing a phage treatment in aquaculture and that was for Vibrio harveyi in shrimp.19 Intralytix Inc. in Baltimore, MD, is also developing a phage treatment against V. tubiashii and related pathogens in larval oyster and clam hatcheries (personal communication). There are numerous reviews on the use of phage therapy for various animals; however, there are relatively few reviews on the use of phages for treating fish and shellfish in aquaculture settings including those by Almeida et al.,3 Oliveira et al.,21 Sanmukh et al.,22 Nakai and Park,23 and Nakai24. This paper reviews available literature on the use of phages for treating specific pathogens in aquaculture products.