In general,

opacification activity

In general,

opacification activity was evaluated using horse serum (Rakonjac et al., 1995; Courtney et al., 1999; Gillen et al., 2002). We also investigated serum opacification using sera obtained from other sources (horse, pig, cow and human). In the culture supernatants of fish isolates, the strongest reaction was observed when fish serum was used as the substrate. In the opacity reaction, SOF targeted high-density lipoprotein (HDL) particles as the substrate (Courtney et al., 2006). Therefore, the turbidity, which may be attributed to the number of HDL particles, was higher in fish serum than in other sera. Previous studies demonstrated that when the serum agar overlay method using SDS–PAGE was adopted, an opaque band appeared on the serum agar (Rakonjac et al., 1995; Courtney et al., 1999; Gillen et al., 2002). The present study

was able to detect no band on the serum agar with Selleckchem MG 132 SDS-PAGE. Sufficient SOF activity of rSOF-OFD could be determined even if the rSOF-OFD sample was heated for 5 min at 100 °C. Meanwhile, addition of SDS to the sample solution apparently attenuated the opacification reaction in fish serum (data not shown). Labile apoA-1 of HDL has been shown to be required for the opacification reaction in serum (Han et al., 2009). In this study, although we have not determined whether SDS is acting directly on SOF or on fish HDL, it is possible that SDS affects apoA-1 of fish HDL and then prevents the opacification reaction. In addition, apoA-1 of fish HDL could be more labile and sensitive to SDS than that of human or other mammals. The expected size of the immune stained band detected by the Western blotting

with the anti-His tag was approximately half that of the opaque band detected by the serum agar overlay method with a native-PAGE check gel. Previous studies reported that the molecular mass of recombinant SOF was much larger than predicted and might be responsible for a dimer of SOF (Courtney et al., 1999; Katerov et al., 2000). Therefore, rSOF-OFD may also form a dimer, and the SDS disassociated the rSOF-OFD molecules. Further studies are in preparation to investigate the different molecular sizes. The serum opacification activity in S. dysgalactiae has been reported only in strain S2 isolated from bovine (Courtney et al., 1999). In this study, a novel variation of the sof gene, sof-FD, and the SOF activity of GCSD strains isolated from farmed fish were determined. SOF was demonstrated to be a virulence determinant of S. pyogenes and S. suis (Baums et al., 2006; Timmer et al., 2006; Gillen et al., 2008). However, the role of SOF-FD in GCSD isolates was not clear. Further studies on SOF-FD may elucidate the mechanism of the virulence determinant in fish isolates. This study was supported by a Grant-in-Aid for Scientific Research from the Ministry of Education, Science, Culture and Sports, Japan (21580229).

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