Effect of high- and low-molecular-weight components of Lactobacillus casei on resistance against Babesia microti in NIH mice.

Three assays were carried out in order to assess the effect of low- and high-molecular-weight components (LMWc and HMWc, respectively) of Lactobacillus casei on the resistance of mice to Babesia microti infection. In the first study, 23 components were identified in a total extract of L. casei by SDS-PAGE. In the second experiment, 15 components (ranging from 19 to 148 kDa) from L. casei (viable) and 12 other components (from 21 to 148 kDa) from L. casei (dead) were recognized by the sera of immunized mice in the extracts of sonicated L. casei. On the basis of these results, samples of sonicated L. casei were separated by preparative gel electrophoresis, and then those gel fragments containing the HMWc (range 63 to 111 kDa) and LMWc (range 19 to 59 kDa) were cut and eluted to constitute the LMWc and HMWc of L. casei. In the third study, five groups of 6 mice each received the following treatments: PBS in the control (C) group, L. casei LMWc in the LcL group, L. casei HMWc in the LcH group, total sonicated L. casei (LMWc + HMWc) in the LcT group, and viable L. casei in the LcV group. At day 0 each mouse in all groups was challenged with 2 x 10(4)B. microti parasitized erythrocytes. At day 8 after challenge, the average percentage of parasitized erythrocytes +/- SEM was significantly higher (P < 0.05) in the C group (11.8 +/- 0.9) as compared with LcL (7.7 +/- 1.5), LcH (10.3 +/- 6.9), LcT (3.6 +/- 0.7), and LcV (6.9 +/- 1.9) groups. The results suggest that L. casei LMWc can induce an early protective immune response, similar to that generated by LcV in mice, against B. microti infection.