Inhibition of Growth of Clostridium botulinum by Intestinal Microflora Isolated from Healthy Infants

Abstract

Infant botulism results when Clostridium botulinum spores germinate, colonise, and produce botulinum neurotoxin in the intestine. As the normal intestinal microflora is important in resistance to C. botulinum colonisation in the mouse model of infant botulism, we investigated the effect of intestinal bacteria isolated from six healthy infants (two breastfed, two formula-fed, and two both formula and breast-fed) on the growth of 14 strains of C. botulinum (three Type A, four Type B, three Type E, two Type F, and two Type G) using zone inhibition procedures. We tested 88 anaerobic and 64 aerobic and facultative isolates. Strains of bifidobacteria, lactobacilli, propionibacteria and enterococci inhibited the growth of C. botulinum, as did several strains of the Bacteroides fragilis group. The only Clostridium inhibiting C. botulinum growth was C. ramosum, which inhibited both of the Type G strains and one of the two Type F strains. At least two bacterial isolates from each faecal sample inhibited most of the 14 C. botulinum strains. Co-culture experiments with intact faecal samples and C. botulinum spores or vegetative cells indicated that the normal flora of healthy infants had a bacteriostatic, rather than a bacteriocidal, effect on the growth of C. botulinum. Thus, susceptibility to infant botulism may result in part from the absence of these inhibitory organisms from the normal flora of the infant intestine.

Key Words:

• Infant botulism
• Colonisation resistance
• Bacterial antagonism
• Clostridium botulinum