Evolution of the digestive microflora in a unit of specified-pathogen-free mice: efficiency of the barrier.

RhoIco strain], barrier-maintained since 1970, is described. Some "contaminants" appeared spontaneously during the period 1971-1973, but microorganisms belonging to the genera Lactobacillus Streptococcus, Enterobacteria, Escherichia and Bacillus remained stable. The methods of investigation used were not suitable for the assessment of strictly anaerobic strains. The stability of the digestive microflora durine the last 2 years of this study is believed to be related to the skill and conscientiousness of the technicians responsible for the daily care of these mice.