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Piscirickettsia salmonis is the etiologic agent of piscirickettsiosis, an economically significant disease of fish. Isolation of P. salmonis by culturing on fish cell lines has been the standard technique since the initial isolation of the organism. The ability to grow P. salmonis on artificial media would relieve facilities of the cost of maintaining cell lines, permit isolation at fish culture sites with fewer contamination problems, and allow easier transport of isolates to diagnostic facilities for confirmation assays. This report describes the successful culture of P. salmonis on enriched blood agar.

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BACKGROUND Among various cardiac autoantibodies (AAb), those recognizing the β1 adrenergic receptor (β1AR) demonstrate agonist-like effects and induce myocardial damage that can be reversed by β-blockers and immunoglobulin G3 (IgG3) immunoadsorption. OBJECTIVES We investigated the role of β1AR-AAbs belonging to the IgG3 subclass in patients with recent-onset cardiomyopathy. METHODS Peripheral blood was drawn at enrollment in subjects with recent-onset cardiomyopathy (left ventricular ejection fraction [LVEF] ≤0.40; <6 months). Presence of IgG and IgG3-β1AR-AAb was determined and echocardiograms assessed at baseline and 6 months. Subjects were followed for up to 4 years. RESULTS Among the 353 enrolled subjects, 62 (18%) were positive for IgG3-β1AR-AAb (IgG3), 58 (16%) were positive for IgG but not IgG3 (non-IgG3), and the remaining were negative. There were no significant differences in baseline systolic blood pressure, heart rate, or LVEF among the groups at baseline. LV end-diastolic and end-systolic (LVEDD and LVESD, respectively) diameters were significantly larger in the non-IgG3 group compared to the other groups (LVEDD: p < 0.01; LVESD: p = 0.03). At 6 months, LVEF was significantly higher in the IgG3 group (p = 0.007). Multiple regression analysis demonstrated IgG3-β1AR-AAb was an independent predictor of LVEF at 6 months and change in LVEF over 6 months, even after multivariable adjustment (LVEF at 6 months, β = 0.20, p = 0.01; change in LVEF, β = 0.20, p = 0.008). In the subjects with high New York Heart Association functional class (III or IV) at baseline, the IgG3 group had lower incidence of the composite endpoint of all-cause death, cardiac transplantation, and hospitalization due to heart failure, whereas the non-IgG3 group had the highest incidence of the composite endpoint. CONCLUSIONS IgG3-β1AR-AAb was associated with more favorable myocardial recovery in patients with recent-onset cardiomyopathy.

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Piscirickettsiosis pathogenesis was examined using some tissues as entry portals of Piscirickettsia salmonis in coho salmon. Juvenile fish, weighing approximately 8.4 g, were used in this trial. Inocula were prepared using the strain SLGO-95 of P. salmonis. The micro-organism was cultured in the CHSE-214 cell line as described by Fryer et al. (1990) and doses containing 10 4.7 and 10 3.7 TCID 50 were prepared. Each dose was used to infect the fish via skin, gills and intestine. Skin and gills were exposed by calibrated drops, and the intestine by an intubation through the anal opening. Some fish were injected intraperitoneally with the same P. salmonis doses, as positive virulence controls. Sham-inoculated fish for each of the tested routes were also included as negative controls. Piscirickettsiosis was experimentally reproduced with all the inoculation methods. Cumulative mortalities and survival analyses showed that the most effective entry portal was skin followed by intestinal intubation and finally by gill infection. KEY WORDS: Piscirickettsia salmonis · Pathogenesis · Fish disease · Coho salmonResale or republication not permitted without written consent of the publisher

Piscirickettsia salmonis is a pathogenic bacterial agent causing septicaemic disease in salmon. Since its isolation in Chile in 1989, P. salmonis has continually produced high mortality rates in salmon farms. Little information exists regarding the mechanisms of vertical transmission of this pathogen. Experimental vertical transmission was established in the present study by inoculation of male and female rainbow trout broodstock with P. salmonis. The bacterium was subsequently detected using indirect immunofluorescence in milt and coelomic fluid of the majority of inoculated broodstock (14/15). Bacteria were detected in the fry when 1 or both parents were inoculated, although none of the infected fry presented signs of the disease. P. salmonis was also detected in progeny obtained through fertilisation ova from non-inoculated females incubated in a medium containing a bacterial suspension, demonstrating transmission during the process of fertilisation. Ova infected in vitro were examined at sample periods from 30 s to 60 min using scanning electron microscopy. This demonstrated that the bacterium attaches to the ova by means of membrane extensions, structures which we have called 'piscirickettsial attachment complex' (PAC) and which would allow later penetration into the ovum.