Protective effect of sera raised against different fractions of Streptococcus suis type 2.

Five bands of 44, 54, 78, 86 and 94 kD were identified by Western blot analysis of Streptococcus suis type 2 by the use of sera that were from immune or non-immune pigs and were positive or negative in bactericidal tests in vitro. These bands were cut from the gels and used as antigens to produce antisera in rabbits. Rabbit sera against the 78 and 94 kD bands were positive in bactericidal tests, and the serum against the 94 kD band also protected mice against challenge with a live pathogenic strain of S. suis type 2. The serum raised against the 78 kD band was not protective in mice and appeared to inhibit the protective effect of the 94 kD band antiserum. Rabbit sera raised against the 44, 54 and 86 kD bands were negative in bactericidal tests and failed to protect mice against challenge.