Edwardsiella bacteria infect Japanese medaka Oryzias latipes; however, the difference in susceptibility between E. piscicida and E. anguillarum is unknown. In this study, we performed challenge ...tests with medaka using four Edwardsiella strains, which were difficult to be identified by specific primers. The four strains were reclassified as three E. piscicida strains and one E. anguillarum strain using phylogenetic analysis. The immersion challenge demonstrated that medaka were more susceptible to E. piscicida than to E. anguillarum. Increases in the bacterial copy number in the infected medaka kidneys were correlated with the worsening of the external symptoms. Medaka is considered a valuable model organism for understanding the etiology of edwardsiellosis.
A pseudotuberculosis pathogen, Photobacterium damselae subsp. piscicida (Pdp), has caused enormous economic damage to yellowtail aquaculture in Japan. The Ivy gene has been discovered in plasmid of ...Pdp, and it has been proposed that it may help bacteria evade lysozyme-mediated lysis during interaction with an animal host. However, the lysozyme-inhibiting activity of Pdp-derived Ivy (Ivy-Pdp) is unknown, and it is unclear whether it acts as a virulence factor for host biophylaxis. In this study, the inhibitory effect of Ivy-Pdp on lysozyme was evaluated by expressing and purifying the recombinant Ivy-Pdp protein (rIvy-Pdp). The rIvy-Pdp protein inhibited hen egg white lysozyme activity in an rIvy-Pdp-concentration-dependent manner, and its inhibitory effect was similar under different temperature and pH conditions. The serum and skin mucus of the yellowtail (which is the host species of Pdp), Japanese flounder, and Nile tilapia showed bacteriolytic activity. In contrast, the addition of rIvy-Pdp inhibited the lytic activity in the serum of these fish species. In particular, it significantly inhibited lytic activity in the serum and skin mucus of Nile tilapia. On the basis of these results, we suggest that Ivy-Pdp is a temperature- and pH-stable lysozyme inhibitor. Additionally, Ivy-Pdp inhibited the lytic activity of lysozyme, which is involved in host biophylaxis. In summary, we inferred that Ivy-Pdp is an important factor that diminishes the sterilization ability of C-type lysozyme when Pdp infects the host.
•Ivy-Pdp highly preserved the CKPHDC motif, as with Ivy derived from known pathogenic bacteria.•Ivy-Pdp inhibited HEWL lytic activity, regardless of temperature and pH.•Ivy-Pdp inhibited lytic activity of yellowtail and Nile tilapia serum.
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GEOZS, IJS, IMTLJ, KILJ, KISLJ, NLZOH, NUK, OILJ, PNG, SAZU, SBCE, SBJE, UILJ, UL, UM, UPCLJ, UPUK, ZAGLJ, ZRSKP
Intracellular bacteria such as those belonging to the genus
Edwardsiella
can survive and proliferate within macrophages. However, the detailed mechanisms underlying the host macrophage immune ...response and pathogen evasion strategies remain unknown. To advance the field of host macrophage research, we successfully established transgenic (Tg) Japanese medaka
Oryzias latipes
that possesses fluorescently visualized macrophages. As a macrophage marker, the macrophage-expressed gene 1.1 (
mpeg1.1
) was selected because of its predominant expression across various tissues in medaka. To validate the macrophage characteristics of the fluorescently labeled cells, May-Grünwald Giemsa staining and peroxidase staining were conducted. The labeled cells exhibited morphological features consistent with those of monocyte/macrophage-like cells and tested negative for peroxidase activity. Through co-localization studies, the fluorescently labeled cells co-localized with
E. piscicida
in the intestines and kidneys of infected medaka larvae, confirming the ingestion of bacteria through phagocytosis. In addition, the labeled cells expressed macrophage markers but lacked a neutrophil marker. These results suggested that the fluorescently labeled cells of Tg
mpeg1.1
:mCherry/mAG medaka were monocytes/macrophages, which will be useful for future studies aimed at understanding the mechanisms of macrophage-mediated bacterial infections.
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EMUNI, FIS, FZAB, GEOZS, GIS, IJS, IMTLJ, KILJ, KISLJ, MFDPS, NLZOH, NUK, OILJ, PNG, SAZU, SBCE, SBJE, SBMB, SBNM, UKNU, UL, UM, UPUK, VKSCE, ZAGLJ
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