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From diseased wild and cultured Oreochromis niloticus in Lower Egypt, 17 Aeromonas hydrophila isolates were recovered. The mortality was between 10% and 70% in among cultured fish. The course of the disease ran in an acute manner. For cultured fish, the disease outbreaks were found mainly in winter and for the wild Nile fish, mortalities were observed in late spring and summer. Additionally wild fish were affected with ectoparasites. The LD50 values of the isolates ranged between 10(3) and 10(7). Isolates of high virulence were resistant to 1 hr boiling and to the bactericidal effect of fresh normal guinea pig serum. Moreover, they did not agglutinate in acriflavin. Only the virulent isolates could agglutinate tilapia erythrocytes. The above effects were reversed for avirulent isolates while moderately virulent isolates showed no consistency in their reactions. Tube agglutination test using O and WC antisera prepared against 6 isolates versus O and WC antigens of 17 isolates indicated an antigenic heterogenicity of different isolates. While some isolates were identical, 4 antigens out of 17 did not react with any of the sera.

During a systemic investigation into O-antigenic relations within the family Enterobacteriaceae, with special emphasis on serological relationships between O-antigens (or O-groups) of E. coli and various O-groupps of Salmonella, Arizona, and Citrobacter, our tests confirmed some findings previously descried by other authors, some were not confirmed, and other antigenic relationships were discovered which have not yet been published. Individually tested were O-Antigens of 142 serologically defined E. coli types by using O-factorsera of Salmonella, Arizona, and Citrobacter for the slide agglutination. The slide agglutination was applied in preference to the tube-agglutination, not only because the former has been generally adopted but it also shows broader reactions...