APPENDIX M 
Dr. Donald Frederickson 
July 14. 1977 
Dr. Anderson did point out, hov^ever, that the non-conjugative plasmid could 
be mobilized in vitro under ideal laboratory conditions in three of the 
eight subjects when indigenous E. coli were randomly selected from their 
feces . 
Dr. R. Curtiss described in vitro transfer experiments in which he 
measured the mobilization of a series of recently developed, non-conjugative 
plasmids under optimal laboratory conditions. He estimated that the maximum 
probability for transmission of such plasmid vectors from an E . col i K12 
host is 10“^^ per surviving bacteria, per day in the intestinal tract of 
warm-blooded animals. He emphasized that the chance of transfer is even 
less than this, since other factors, not taken into account, would reduce 
transfer in the intestinal tract. These in vivo deterrents include: 
(1) diminished bacterial metabolic activity leading to decreased conjugation. 
In the test-tube, the generation time of E. coli is 20-40 minutes, but is 
8-12 hours in the intestinal tract; (2) conjugation is inhibited by fatty 
acids, bile and other constituents of the gut; and (3) conjugation is 
inefficient at the pH and Eh (oxidation-reduction potential) of the 
intestine. 
It was the consensus of the group that the possibility of transfer of 
a non-mobil izable plasmid from E. coli kl2 to a wild-type strain in vivo 
is extremely unlikely. However, it was recommended that animal and human 
feeding experiments sould be performed, to confirm the previous observations 
in man and to provide further assurance that in vivo transfer of these 
plasmids would not occur. Such studies should receive the highest priority. 
Sincerely yours 
Sherwood L. Gorbach, M.D. 
Chief, Infectious Disease 
Professor of Medicine and 
Microbiology 
Tufts University School of 
Medicine 
SLG:cls 
CC: All Workshop participants 
Appendix M--5 
