Isolation of antibiotic-resistant lactobacilli.

Numerous studies have been concerned with effects of orally administered antibiotics upon the numbers and kinds of microorganisms in the feces of man, but the influence of antibiotics upon intestinal lactobacilli, shown by changes in the numbers and kinds of these bacteria in feces, has not been thoroughly investigated. Enumeration and isolation of fecal lactobacilli have been facilitated by the development of a Lactobacillus selective medium (LBS) by Rogosa et al. (1951). However, the usual method of isolating pure cultures of lactobacilli from petri dish cultures involves picking colonies from a deep layer of the selective medium. If this procedure were to be used for detection and isolation of antibioticresistant lactobacilli, it would necessitate expenditure of considerable time and material. Therefore, the technique to be described was developed to detect antibiotic-resistant lactobacilli and to isolate them by a replica plating procedure.