8 
A. M. Skalka 
APPENDIX II 
Summary of Conclusions from Feeding 
and Monitoring Experiments^ 
by Dr. M. Richmond, Bristol 
1. J£. coli K12, even prototrophs, fed to man and livestock in high dose will 
generally survive about 4 days, although in a few individuals the organism can 
be detected by selective methods for nearly 2 weeks. The organism may multiply 
to a limited extent with 24-28 hours after administration but generally does 
not undergo more than a few doublings. 
2. If the K12 JE. coli that are fed carry a self-transf erring plasmid that is 
de-repressed, the plasmid will be transmitted to the^gecipient flora. Trans- 
con jugants are found at a frequency of about 1 x 10 of all IS. coli shed per 
day. No evidence for the mobilization of non-transferable plasmids from E. 
coli K12 has been found for naturally occurring F group or I group R plasmids. 
We think it unlikely that such transfer would occur with approved cloning 
vectors. This conclusion is supported by in vitro mobilization experiments. In 
vivo survival of EK-2 strains and their potential transfer of either conjugatlfve 
or non-conjugative plasmid must be considered to be below the current limits of 
experimental detection. 
3. IS. coli K12 strains which survive passage through the human or animal gut 
rarely show evidence of having acquired plasmids from the indigenous flora. In 
a calf-feeding experiments, only 1 out of well over 10,000 K12 strains which 
were screened had acquired colicinogeny. 
4. Over a period of 26 months in Bristol, 12 months in London and 12 months in 
Seattle involving 64 subjects, there was no evidence that laboratory workers, 
or members of their families, acquired either bacterial strains or plasmids 
that were employed in the laboratory. This was true even in a few individuals 
working in the laboratory who received short courses of antibiotic therapy or, 
in one case, an individual who was on prophylactic antibiotic therapy. Moni- 
toring of the oropharynx failed to show any evidence of colonization by labora- 
tory strains. Individuals with excessive facial hair likewise showed no evidence 
of carriage. In a few instances, individuals who had done routine experimental 
procedures (vortex mixing, or plating, etc.) showed transient numbers of E. 
coli K12 on their laboratory garments, facial skin or hands. These organisms 
were few in number (4/cu “) and disappeared within three hours. Simple washing 
with soap and water resulted in instantaneous loss of these organisms. No 
evidence whatsoever was found for even transient survival of JE. coli EK-2 
derivatives . 
2 
The following Report was presented by M. H. Richmond to the Meeting of the 
Risk-Assessment Sub-Committee of COGENE which met at the Royal Society, London, 
on Friday, March 30th, 1979. The Report was compiled by Dr. Stanley Falkow on 
the basis of information provided by himself, by E. S. Anderson and by M. H. 
Richmond. The information contained in the Report represents the situation as 
it was at the end of October 1978, save that the data from Bristol have been 
updated to include information up to the end of 1978. 
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