In vitro and in vivo neutralizing activity of human colostrum and milk against purified toxins A and B of Clostridium difficile.

The neutralizing activity (NA) of supernates of colostral samples collected postpartum from 55 women and tested against a 50% cytopathic dose of purified toxins A and B of Clostridium difficile was evaluated in Y1 adrenal cells. Thirty-one (56%) of the samples had NA against one or both toxins. Samples of breast milk were collected postpartum from five women-three had colostral NA and two did not. All milk specimens from the three women with colostral NA had NA titers of 1:1-1:4 throughout the study (609 days in one case). Samples from the two women without colostral NA did not exhibit NA during a 60-day follow-up period. In suckling mice either toxin plus human milk with in vitro NA elicited significantly less fluid accumulation than did toxin plus diluent or toxin plus milk without in vitro NA (P less than .025 to P less than .05). Twelve (63%) of 19 milk samples with in vitro NA against toxin A and 15 (65%) of 23 with in vitro NA against toxin B inhibited fluid accumulation caused by the corresponding toxin. In vitro NA against toxin A appeared to reside in the secretory IgA fraction of one milk sample assessed by immune precipitation. The results suggest that human milk may protect newborn infants against toxins A and B of C. difficile.