PERSISTENCE OF INDIVIDUAL STRAINS OF ESCHERICHIA COLI IN THE INTESTINAL TRACT OF MAN

There is ample evidence that man invariably acquires E8cherichia coli during the first day or two of life, if not, indeed, even before birth, and that he is never thereafter without it. The constancy of this occurrence makes it a safe presumption that every day throughout life new strains of this organism are introduced into the intestinal tract. If all strains established themselves there and multiplied with equal facility, one would expect that the strain composition of the E. coli of the feces of any individual over a period of time would present an exceedingly complicated and constantly changing picture. There are so many unknown factors involved in this picture, however, that inferences are of little value unless supported by observed facts. For most organisms there would be no way to study the strain composition of material containing them, but the great antigenic diversity of E. coli offers an opportunity to determine at least whether the number of strains present at any one time is small or large and whether individual strains tend to persist over long periods or whether their tenure is very brief. Two studies have been made in recent years that throw some light on this subject. Kauffmann and Perch (1943) studied two persons over a period of approximately 4 months, plating out stool specimens from each at irregular intervals, selecting 2 to 4 colonies from each plate and classifying them with respect to their 0 groups. The results from one of their subjects revealed one to three different antigenic groups in each specimen. In only one instance was the same group found in two specimens, and in this case the interval between its first and last appearance was so long (90 days) as to suggest that it more likely represented the appearance of a new strain of the group than the persistence in the bowel of the original one. Their other subject, however, yielded the same antigenic group in each of 10 successive specimens collected over a period of 42 days, together with occasional more transient groups, and after its disappearance another group appeared in 3 successive specimens collected during a period of 58 days. Waliick and Stuart (1943) made a study on a single subject, collecting specimens at more frequent and more regular intervals and picking 10 colonies from each specimen. Their study continued over a period of 15 months and revealed a more or less definite pattern in the E. coli strain composition of the feces of the individual studied. Three of their antigenic groups were almost continuously present for several months each, but not concurrently, though there was some overlapping. Along with these, in most specimens, there appeared from one to three others that were either not found at all in later specimens or in only a few successive