In view of the ubiquitous nature of E. coli , the fact 
that all strains including K-12 already have the capacity 
for human infection, and E. coli 1 s ability to exchange 
genetic material with other bacteria, the deliberate 
genetic modification of even "weakened" strains of E. coli 
poses a potentially serious threat to human health. 
2. DNA can be taken from organisms that produce toxins 
(e.g. botulnum) creating the possibility that the host 
organism, which occupies a different ological niche, 
will acquire the ability to produce the toxin. 
This would be particularly serious if such genes were 
expressed in strains of E. coli capable of colonizing 
the human colon. 
3. Genes which code for resistance to antibiotics are 
transferred by some recombinant DNA experiments to 
strains of bacteria that were not previously resistant. 
4. The animal virus on which the most genetic information 
is available is simian virus 40 (SV-40) , which produces 
tumors in some animals and infects humans, although apparently 
with no pathological symptoms. However, the genetic 
basis for- the virus causing tumors in monkeys but not 
humans is not understood. Therefore, the possibility 
exists that even an apparently innocuous modification 
of SV-40 DNA could render the virus tumorigenic or 
otherwise .pathogenic to humans, thus creating a serious 
hazard to human health. Yet it is sy-40, and polyoma 
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