APPENDIX H 
(D) For each mobilizing plasmid, a positive control must be carried 
out under permissive conditions to confirm the efficacy of the test. In 
these control experiments, the donor-mobilizing plasmid system and the 
third, recipient bacterial strain must be the same as used in the above 
experiments; the intermediate host must be a conjugation-proficient 
cell containing an efficiently mobilizable plasmid, such that R x R 
1 2 
-3 
(separately measured) must be equal to or greater than 1x10 in 
the case of derepressed mobilizing plasmids and must be equal to or 
-5 
greater than 1x10 in the case of repressed mobilizing plasmids. 
(E) Six -hour triparental matings must be done in parallel with 
each of the above experiments, and must yield transfer rates (R ) 
3 
for the EK2 plasmid which, in each case, are equal to or less than 
the observed products of R x R 
1 2 
(F) The survival of the EK2 and control hosts during the mating 
periods must be measured, and the transfer rates described above 
must be calculated in terms of the final number of viable EK2 or control 
intermediate hosts. 
Appendix H--9 
