The impact of hospitalization on the aerobic fecal microflora.

Quantitative bacteriological analysis of the aerobic fecal microflora of 75 patients indicated that, at the time of admission to hospital, Escherichia coli were the predominant fecal aerotolerant bacteria. Subsequent fecal samples showed a progressive supplantation of E coli by Klebsiella, Enterobacter and Proteus. At the end of 21 days of hospitalization, E coli remained predominant in only 30 patients. None of the patients had received antibiotics, undergone surgery or been subjected to x-ray studies of the gastrointestinal tract. The cause of the change of fecal flora in these patients is unknown, and no change of flora was observed in a control group of nonhospitalized persons, also studied for 21 days. The appearance of Klebsiella, Enterobacter and Proteus as predominant in the fecal flora of hospitalized patients may be an important factor in the natural history of hospital-associated infections.