McKibben C L, Pascho R J
Biological Resources Division, Western Fisheries Research Center, Seattle, Washington 98115, USA.
Dis Aquat Organ. 1999 Oct 11;38(1):75-9. doi: 10.3354/dao038075.
Laboratory studies of the transmission and pathogenesis of Renibacterium salmoninarum may describe more accurately what is occurring in the natural environment if test fish are infected by waterborne R. salmoninarum shed from infected fish. To quantify bacterial shedding by chinook salmon Oncorhynchus tschawytscha at 13 degrees C in freshwater, groups of fish were injected intraperitoneally with R. salmoninarum at either 1.3 x 10(6) colony forming units (CFU) fish (-1) (high-dose injection group) or 1.5 x 10(3) CFU fish (-1) (low-dose injection group). R. salmoninarum infection levels were measured in the exposed fish by the enzyme-linked immunosorbent assay (BKD-ELISA). At regular intervals for 30 d, the numbers of R. salmoninarum shed by the injected fish were calculated on the basis of testing water samples by the membrane filtration-fluorescent antibody test (MF-FAT) and bacteriological culture. Mean BKD-ELISA optical densities (ODs) for fish in the low-dose injection group were not different from those control fish (p > 0.05), and no R. salmoninarum were detected in water samples taken up to 30 d after injection of fish in the low-dose group. By 12 d after injection a proportion of the fish from the high-dose infection group had high (BKD-ELISA OD > or = 1.000) to severe (BKD-ELISA OD > or = 2.000) R. salmoninarum infection levels, and bacteria were detected in the water by both tests. However, measurable levels of R. salmoninarum were not consistently detected in the water until a proportion of the fish maintained high to severe infection levels for an additional 8 d. The concentrations of R. salmoninarum in the water samples ranged from undetectable up to 994 cells ml(-1) on the basis of the MF-FAT, and up to 1850 CFU ml(-1) on the basis of bacteriological culture. The results suggest that chinook salmon infected with R. salmoninarum by injection of approximately 1 x 10(6) CFU fish (-1) can be used as the source of infection in cohabitation challenges beginning 20 d after injection.
如果用受感染鱼排出的水传播型鲑肾杆菌感染试验鱼，那么对鲑肾杆菌传播和发病机制的实验室研究可能会更准确地描述自然环境中正在发生的情况。为了量化在13摄氏度淡水中奇努克鲑（Oncorhynchus tschawytscha）排出的细菌数量，将鱼分组，分别以1.3×10⁶菌落形成单位（CFU）/鱼（高剂量注射组）或1.5×10³CFU/鱼（低剂量注射组）的剂量腹腔注射鲑肾杆菌。通过酶联免疫吸附测定（BKD-ELISA）测量暴露鱼体内的鲑肾杆菌感染水平。在30天内定期通过膜过滤-荧光抗体试验（MF-FAT）和细菌培养检测水样，计算注射鱼排出的鲑肾杆菌数量。低剂量注射组鱼的平均BKD-ELISA光密度（OD）与对照鱼无差异（p>0.05），在低剂量组注射鱼后30天内采集的水样中未检测到鲑肾杆菌。注射后12天，高剂量感染组的一部分鱼出现高（BKD-ELISA OD≥1.000）至严重（BKD-ELISA OD≥2.000）的鲑肾杆菌感染水平，两种检测方法均在水中检测到细菌。然而，直到一部分鱼在另外8天内维持高至严重感染水平，才在水中持续检测到可测量水平的鲑肾杆菌。基于MF-FAT，水样中鲑肾杆菌的浓度范围为不可检测至994个细胞/毫升，基于细菌培养则高达1850 CFU/毫升。结果表明，注射约1×10⁶CFU/鱼的鲑肾杆菌感染的奇努克鲑可在注射后20天开始用作同居挑战试验中的感染源。
