The specific biochemical characteristics for 25 strains of A. pleuropneumoniae, 35 strains of P. multocida and 50 strains of S. suis isolated from the pneumonia infected pigs in some Northern provinces, Vietnam were identified. Determination of serotype of 25 A. Pleuropneumoniae by PCR technique with electrophoretic product (DNA with the length of 950 bp) indicated that there were 16 strains belonging to serotype 2
6 strains belonging to serotype 5a and 3 strains belonging to serotype 5b. In 16 above mentioned strains, there were 7 strains belonging to apxlllCA/IBD/lIlBD gene combination, 3 strains belonging to apxllCA/IIlCA/IBD/IIlBD gene combination, 3 strains belonging to apxlBDI IIIBD gene combination, 2 strains belonging to apxlCA/IICA/IBD/lIlBD gene combination and 1 strain belonging to apxlllBD gene combination. In 9 strains of serotype 5, there were 8/9 strains belonging to apxlCA/IICA/IBD gene combination, and 1/9 strain belonging to apxlllCA/IBDI IIIBD gene combination. In 35 P. multoeida strains, there were 30 and 5 strains identified belonging to serotype A and serotype D respectively. All of 50 S. suis strains were confirmed to have the same specific electrophoresis product (that is DNA with the length of 688 bp). Of which, 23 strains belonged to serotype 2, 7 strains belonged to serotype 7, 12 strains belonged to serotype 9 and serotype of 8 strains were not identified. The strains belonging to serotype 2 had the most number of gene combination types. They were distributed in 5 gene combinations: arcA, arcA/sly, arcA/mrp, arcA/mrp/sly, arcA/mrp/sly/epf.