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NO46 - 2

In Vivo Analysis on the Adherence and Infection Route of Photobacterium damselae subsp. piscicida in Yellowtail

<>Ichiro Nagano1, Syun-ichirou Oshima1 and Kenji Kawai2*<>1Graduate School of Kuroshio Science, Kochi University, Kochi 783-8502, Japan
2Fish Disease Laboratory, Department of Aquaculture, Kochi University, Kochi 783-8502, Japan
(Received February 10, 2011)

ABSTRACT―Pseudotuberculosis caused by Photobacterium damselae subsp. piscicida is a serious problem in fish culture industry. The initial stage of host-pathogen interaction is primarily important to understand infectious disease. However, the mode of transmission and route of infection of the agent are not fully studied. In this study, changes in the distribution of the bacterium on and in yellowtail Seriola quinqueradiata body during infection process was investigated using immersion challenge. The result revealed that external regions such as the lower jaw, pectoral fin, skin and gills permitted bacterial adherence soon after immersion. Viable bacterial counts increased in the gills soon after infection, then they increased in the blood, spleen and kidney. Moreover, fish were exposed to bacteria at the gills or posterior part of body surface to elucidate the primary infection route. The fish group challenged at gills showed higher mortality than the other group. These results reveal that the gills are the primary regions for P. damselae subsp. piscicida to invade and proliferate in yellowtail.

Key words: bacterial adherence, gill, infection route, in vivo analysis, Photobacterium damselae subsp. piscicida

Infection Dynamics of Microsporidium seriolae (Microspora) Causing the Beko Disease of Seriola spp.

<>Hiroshi Yokoyama1*, Daichi Ayado1, Jiro Miyahara2, Kazuki Matsukura2, Ikuo Takami2, Fumihiko Yokoyama3 and Kazuo Ogawa1<>1Department of Aquatic Bioscience, Graduate School of Agricultural and Life Sciences,
The University of Tokyo, Tokyo 113-8657, Japan
2Nagasaki Prefectural Institute of Fisheries, Nagasaki 851-2213, Japan
3Nagasaki Prefecture Iki District Office, Nagasaki 811-5133, Japan
(Received February 15, 2011)

ABSTRACT―Infection dynamics of Microsporidium seriolae causing the beko disease of yellowtail Seriola quinqueradiata and amberjack S. dumerili were investigated at fish farms and an experimental facility. A 4-year survey (2006-2009) showed a sharp increase in prevalence of infection with M. seriolae in June or July soon after stocking net cages with yellowtail and amberjack wild fingerlings. Most cysts blackened and finally disappeared in November in the following year. However, in 2006 when the levels of infection were relatively high, some visible cysts still remained even in autumn of the following year. Infective periods and effects of fish size on M. seriolae infection were investigated via natural exposure of hatchery-reared yellowtail juveniles by transferring to an open sea cage in an endemic area. Invasion of the parasite into fish occurred in June and July but not after the mid-August. A comparison of M. seriolae infection among four size classes of yellowtail showed that the smallest fish (1 g in mean weight) had the lowest prevalence of infection.

Key words: Microsporidium seriolae, Seriola quinqueradiata, yellowtail, Seriola dumerili, amberjack, infection dynamics, beko disease

Histopathology of Gill Lesions of Ayu Plecoglossus altivelis Clinically Diagnosed with 腺oke・Disease

<>Shinpei Wada1*, Hiroko Atami1, Osamu Kurata1, Kishio Hatai1, Kohichi Kasuya2, Yusuke Watanabe2 and Hideo Fukuda3<>1Laboratory of Fish Diseases, Nippon Veterinary and Life Science University, Tokyo 180-8602, Japan
2Tochigi Prefectural Fisheries Station, Tochigi 32-0404, Japan
3Laboratory of Fish Pathology, Tokyo University of Marine Science and Technology, Tokyo 108-8477, Japan
(Received August 4, 2010)

ABSTRACT―We investigated the histopathological features of the gill lesions of diseased ayu Plecoglossus altivelis that had been diagnosed with 腺oke・ The features were classified into three types: one characterized by atypical gill epithelial cells, one characterized by numerous long Gram-negative rods, and one characterized by both atypical gill epithelial cells and long rods. TEM revealed the presence of poxvirus-like virus in the atypical gill epithelial cells. Our results indicated that 腺oke・was composed of different kinds of diseases. We propose 疎typical cellular gill disease (ACGD)・as the new name of novel gill disease in ayu.

Key words: Boke, gill lesion, histopathology, Plecoglossus altivelis, ayu, atypical cellular gill disease, ACGD

The Use of Chromogenic Media for α-Glucosidase Determination and Presumptive Drug Susceptibility Profiles in the Fish Pathogen Nocardia seriolae

<>Tamer Fawzy Ismail1,2, Akira Takeshita3, Naoko Umeda4, Toshiaki Itami5 and Terutoyo Yoshida5*<>1Interdisciplinary Graduate School of Agriculture and Engineering, University of Miyazaki, Miyazaki 889-2192, Japan
2Department of Veterinary Hygiene and Management, Faculty of Veterinary Medicine, Cairo University Giza, 12211, Egypt
3Kurose Suisan Kaisha Ltd, Miyazaki 888-0012, Japan
4Marine Biological Technology Center, Nippon Suisan Kaisha Ltd, Oita 876-1204, Japan
5Faculty of Agriculture, University of Miyazaki, Miyazaki 889-2192, Japan
(Received January 11, 2011)

ABSTRACT―The utility of chromogenic media for determination of α-glucosidase (α-glu) activity in 116 Nocardia seriolae isolates was investigated. In all isolates, the results obtained using chromogenic media were identical to those of the API ZYM test. All the α-glu-positive isolates (n = 27) were erythromycin (Em)-sensitive, and more than half of them (n = 18) were oxytetracycline (OTC)-resistant. On the other hand, all the α-glu-negative isolates (n = 89) were OTC-sensitive, and most of them (n = 81) were Em-resistant. These results supported the relationship between the α-glu activity and drug susceptibility profiles in N. seriolae. Therefore, chromogenic media can be used as a simple and reproducible one-step test to determine the α-glu activity and presumptive drug susceptibility profiles in N. seriolae.

Key words: Nocardia seriolae, chromogenic medium, α-glucosidase, drug susceptibility, oxytetracycline, erythromycin