APPENDIX H 
prudent to demand that a significant degree of containment be contributed 
by the factors R and R , 
1 2 
-6 
A maximal value of 1 x 10 for the product R x R , for example, 
1 2 
-8 
would give a figure of less than 1x10 for the overall rate of transfer 
-2 
(P X R X P X R ), even if P x P were as high as 1 x 10 , 
112 2 12 
-14 
rather than the observed value of less than 1x10 
In view of these considerations, the investigator is required to 
furnish data from the following types of experiments: 
(A) The rate of transfer (R ) of each of several mobilizing plasmids 
1 
(see below) from their respective donors to the proposed EK2 system 
must be measured under optimal, permissive conditions, using 90- 
minute matings in vitro . 
(B) The rate of transfer (R ) of the EK2 plasmid from the EK2 
2 
system harboring each mobilizing plasmid must be measured under 
optimal, permissive conditions using six -hour matings in vitro . 
(C) The above tests must be done with one mobilizing plasmid 
from each of the following compatibility groups: FII, N, and I. A 
genetically derepressed plasmid should be used in each case, if such 
exists. The product, R x R , must be equal to or less than 
1 2 
-6 
1x10 in the case of derepressed mobilizing plasmids, and must 
-8 
be equal to or less than 1x10 in the case of repressed mobilizing 
plasmids. 
Appendix H--8 
