POSTNATAL CHANGES IN SELECTED BACTERIAL GROUPS OF THE PIG COLONIC MICROFLORA

The importance of the colonic microflora in health and nutrition is we ll known, but how they colonize and become established in the colon is not well understood. We therefore characterized the quantitative and qualitative changes of the colonic microflora during the first 120 day s of postnatal development. Unlike previous studies, changes were defi ned for individual pigs using in situ samples collected anaerobically and aseptically from the distal colon. Although the colons were steril e at birth, they were rapidly colonized, and within 12 h bacterial den sities had stabilized at 10(-9)-10(10) bacteria/g colonic content. Fac ultative anaerobes, notably coliforms, initially dominated the microfl ora, but were supplanted within 48 h after birth by obligate anaerobes , which constituted greater than 90% of the microflora thereafter. Bac teroides spp., the predominant anaerobes in the adult colon, did not m arkedly increase in abundance until after weaning and were still incre asing by postnatal day 120. Shifts in the relative abundances of diffe rent bacterial populations throughout the first 120 days after birth c onfirm previous reports that the establishment of the adult colonic mi croflora is a gradual, sequential process, and highlight the need to f ocus research on anaerobic groups.