APPENDIX E 
individuals refrain from work for the duration of the abnormal situation. 
However, while col i K1 2 does not establish itself as a growing strain 
in normal bowels, it does remain alive during its passage through the tract. 
Therefore transfer of plasmid or bacteriophage vectors containing foreign 
DNA from the original col i K12 host to bacteria resident in the intestines 
or bacteria encountered after excretion must be considered. The guidelines 
specify the use of nonconjugat ive plasmids as vectors in recombinant research, 
because they cannot promote their own transfer. However transfer of a ' 
resident nonconjugative plasmid is possible in nature if the recombinant- 
containing host acquires a conjugative plasmid that is derepressed for 
transfer For any given host-plasmid combination used in a recombinant DNA 
experiment it will be necessary to assess the possibilities for transfer of the 
recombinant DNA in order to evaluate the degree of biological containment. 
While we are missing some relevant information, the available data suggest that 
the probability of transfer can be quite low, depending on the particular 
nonconjugative plasmid used, on whether or not the conjugative plasmid is repressed 
with respect to expression of donor fertility, and on the viability of the host 
cell in natural environments. With certain known and useful plasmids, triparental 
matings involving first the acquisition of a conjugative plasmid and second, 
transfer of the nonconjugative plasmid to a third cell occur at freauencies 
9 
that are less than one in 10 and in fact are usually undetectable under laboratory 
conditions designed to resemble natural conditions. Host-vector systems made up 
of E. col i K12 and such plasmids therefore appear to have only very I imited 
ability to spread recombinant DNA molecules. 
Analogous considerations apply when bacteriophage are to be used as vectors 
Appendix E — 10 
