50 E. coli and 50 Salmonella strains isolated from the edema, diarrhea, and septicemia infected pigs in some northern provinces of Vietnam were being kept at the Department of Bacteriology, NIVR. These bacterial strains were selected for study and production of vaccine. The testing result showed that these bacterial strains have carried the typically biochemical properties of the E. coli and Salmonella genus as described in the published documents. There were 44/50 E. coli strains identified carrying serotype 0 with 10 different serotypes. Of which, serotype 08 accounted for the highest proportion (20.0 percent), followed by serotype 0141, 0149 (16.0 percent) and 0125, 0143, 063 (2.0 percent). Among 50 studied Salmonella strains, 15 strains belonged to S. choleraesuis and 35 strains belonged to S. typhimurium. Result of testing 50 E. coli strains showed that they were positive with one or more pathogenic factors. The rate of strains carrying adhesive factor F18 was 50.0 percent and F4 was 32.0 percent
a number of strains carrying toxin VT2e accounted for the highest rate with 74.0 percent, followed by toxins STa, LT and STb with 56.0 percent, 52.0 percent and 34.0 percent, respectively. Among 15 S.choleraesuis strains, 13 strains carried gene Stn (86.7 percent) and 14 strains carried gene InvA (93.3 percent). Number of S.typhimurium carrying gene Stn was 27/35 strains (77.1 percent) and carrying gene InvA was 29/35 strains (82.9 percent). The studied E. coli and Salmonella strains showed high virulence when testing on experimental mice and swines. A multivalent inactivated vaccine produced from 6 selected E. coli strains and 3 selected Salmonella strains has achieved the criteria of sterility (100 percent), safety (100 percent) and high protective effect (100 percent) when testing on the experimental animals.