Figure 3.

A modified commensal donor E. coli strain colonized the mouse gut in the absence of antibiotic selection pressure. (A) The total number of bacteria with and without RP4 plasmid is shown for each mouse as determined by serial dilution plating on MacConkey agar containing chloramphenicol. (B) The number of bacterial cells carrying RP4 plasmid (donor bacteria) on different days of the ten-day experiment was determined by serial dilution plating on MacConkey agar containing chloramphenicol and ampicillin. Each symbol represents an individual mouse (n = 5). Mouse 1 remained negative for donor bacteria after 24 h. Two mice (n = 2) were in the control group given Luria broth only. The lower limit of detection was 100 CFUs per gram of fecal material.