Kinetics of B cell response during Yersinia enterocolitica infection in resistant and susceptible strains of mice

In this study we analyze the B-cell response in murine yersiniosis. To this end, we determined whether polyclonal activation of B-lymphocytes occurs during infection of susceptible (BALB/c) and resistant (C57BL/6) mice with Y. enterocolitica 0:8 and compared the immunoglobulin (Ig) isotypes produced in response to the infection by the two strains. The number of splenic cells secreting nonspecific and specific immunoglobulins was determined by ELISPOT. The presence of anti-Yersinia antibodies in serum was detected by ELISA. In both strains, the number of specific Ig-secreting cells was relatively low. Polyclonal B-cell activation was observed in both strains of mice, and the greatest activation was observed in the BALB/c mice, mainly for lgG(1)- and IgG(3)- secreting cells. The C57BL/6 mice showed a predominance of IgG(2a)-secreting cells. The peak production of anti-Yersinia IgG antibodies in the sera of BALB/c mice was seen on the 28th day after infection. The greatest increase in IgM occurred on the 14th day. A progressive increase of specific IgG antibodies was observed in C57BL/6 mice up to the 28th day after infection while IgM increased on the 21st day after infection. The production of specific IgA antibodies was not detected in either BALB/c or C57BL/6 mice. We conclude that polyclonal. activation of B lymphocytes occurs in both the Yersinia resistant and Yersinia-susceptible mice and that the more intense activation of B lymphocytes observed in the susceptible BALB/c mice does not enhance their resistance to Y. enterocolitica infection.

AN IMPROVED ENRICHMENT PROCEDURE FOR THE ISOLATION OF YERSINIA-ENTEROCOLITICA AND RELATED SPECIES FROM MILK

A new enrichment procedure is proposed to improve the isolation of Yersinia enterocolitica and related species from milk. This procedure uses tryptic soy broth plus Polymyxin (5 IU/ml) and Novobiocin (10 mug/ml) - TSPN broth - incubated at 18-degrees-C for 3 d. Using raw milk and pasteurized milk inoculated with Yersinia strains, the efficiency of this procedure was compared to that of SB broth (sorbitol bile salts broth) incubated at 4-degrees-C for up to 21 d. Despite of the presence of antibiotics in TSPN broth, there were difficulties in recovering Yersinia organisms. Nevertheless, TSPN broth incubated at 18-degrees-C for 3 d showed better efficiency than that other method. In pasteurized milk samples, TSPN medium at 18-degrees-C for 3 d gave better results than the SB broth at 4-degrees-C for 7 d, showing that the proposed procedure is the preferable one due to the shorter period of incubation.