Development of faecal flora was studied in seven very low birth weight (VLBW) infants, who were fed on human milk and whose birth weights ranged from 810-1350 g. The intestine of the VLBW infants was first colonised by enterobacteria and streptococci, as it was in full-term infants. VLBW infants differed, however, from full-term infants in that both types of organism continued to be predominant for a longer period, and establishment of bifidobacterial flora was retarded. Bifidobacteria first appeared in the stools of VLBW infants at a mean age of 10.6 +/- 2.7 days and became predominant at a mean of 19.8 +/- 8.9 days, in contrast to full-term, breast-fed infants in whom bifidobacterial flora appeared at as early as 4 days of age. The delay seemed to be related to the low milk intake of the VLBW infants. The number of viable staphylococci in the stools of VLBW infants was generally higher than that in full-term infants. Although emergence of Bacteroides, Clostridium and lactobacilli was delayed compared with full-term infants, differences in their occurrence and prevalence between VLBW and full-term infants were not remarkable.

The development of stool bacterial flora was studied in breast-fed and bottle-fed infants. In both groups of infants, the intestine was first colonized with enterobacteria and their number attained 109 per gram of feces. On day 6, bifidobacteria were the predominant organisms in the stool of breast-fed infants, exceeding enterobacteria by a ratio of 1,000:1, whereas enterobacteria were the predominant organisms in formula-fed infants, exceeding bifidobacteria by approximately 10:1. At 1 month of age, bifidobacteria were the most prevalent organisms in both groups but the number of these organisms in the stool of bottle-fed infants was approximately one tenth that of breast-fed infants. The properties of breast milk that promote the growth of bifidobacteria and suppress the growth of coliform and other potentially pathogenic organisms, theoretically, would help to minimize the incidence of neonatal diseases caused by these organisms. The results would support the advantages of breast-feeding for optimal care of newborn infants.

Influences of antibiotics on the fecal flora in children were studied for oral ampicillin, penicillin V, erythromycin, cefaclor, and gentamicin and for intravenous ainpicillin, methicillin, cefpiramide, and ceftazidime. AU antibiotics affected the normal flora, although the quality and quantity of the changes were variable. No substantial differences were noted between the oral and intravenous use of ampicillin with regard to its effect on the flora. Three penicillins, ampicillin, penicillin V, and niethicillin, caused remarkable changes. The characteristic pattern observed was the considerable suppression of Bifidobacterium, Streptococcus, and Lactobacillus species. Although enterobacteria did not significantly change in number, Klebsiella spp. frequently replaced Escherichia coli. In patients given erythromycin and cefaclor, the reduction in the number of Bifidobacterium spp. was 1 logio and that of members of the family Enterobacteriaceae was 3 log1o.Gentamicin administered orally caused a drastic change, including a remarkable decline, of E. coli to less than 2 loglo/g of feces. Cefpiramide, a parenteral expanded-spectrum cephalosporin, suppressed normal flora so markedly that almost all species of organisms were eradicated, and the active growth of yeasts was promoted (2.6 loglo increase). Ceftlzidime caused similar changes as cefpiramide, but the changes were less extensive.

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