Bacteroides species in the normal neonatal faecal flora.

Bacteroides spp. were isolated from the faeces of neonates and identified by rapid modifications of established conventional methods. Gram-negative anaerobic bacilli were recovered from 12 out of 16 neonates and a heavy growth of Bacteroides spp. was obtained from all 12 specimens. Twelve representative isolates from each subject were selected for identification; 141 of the 144 Bacteroides isolates belonged to the B. fragilis group and three to the B. melaninogenicus/oralis group. Eight species were represented within the B. fragilis group. B. vulgatus (c. 46%) and B. thetaiotaomicron (c. 30%) were the predominant species. B. fragilis, the type-species of the group, formed only a small proportion of neonatal faecal flora. The proportional representation of individual species were similar to that found in adults but B. asaccharolyticus was not represented.