ESCHERICHIA-COLI K12 DOES NOT COLONIZE THE GASTROINTESTINAL-TRACT OF FISCHER-344 RATS

The colonizing potential of Escherichia coli K12 containing a vector c oding for somidobove (bovine somatotropin) was determined. Treated mal e and female Fischer-344 rats were given a single oral gavage inoculum of sucrose with/without tetracycline (15 mug/ml). Untreated control a nimals received similar drinking water regimes. All animals survived u ntil termination. There were no clinical signs of toxicity observed an d no treatment-related effect upon body weight, food consumption, or e fficiency of food utilization. Fresh fecal samples were collected from each rat every 24 h following inoculation and the population of the m arked strain was quantitated until no bacterial colonies were observed for two consecutive days. While all inoculated rats were positive at 24 h, by 72 and 96 h all had become negative for the test (marked) str ain, as were the corresponding control group throughout the test. The frozen stock of the marked strain used as the positive control demonst rated that the agar plates were selective for the test strain. Fourtee n days following inoculation, all groups of rats were killed and the g astrointestinal tracts removed and treated to recover the marked strai n. There was no evidence of the marked strain in the gastrointestinal tract of any rat from any group. Thus, the E. coli K 12 host/vector sy stem used in this experiment does not colonize the gastrointestinal tr act of Fischer-344 rats.