-3- 
3) High-This type of containment involves facilities which are 
isolated from other areas by air locks, clothing changes and shower rooms and 
which have treatment systems to inactivate or remove biological agents that 
may be contaminants in exhaust air, liquid and solid wastes. The handling of 
agents shall bo confined to biological safety cabinets and all persons occupying 
these areas shall wear only laboratory protective clothing and shall shower at 
each exit from the containment facility. In addition the containment facility 
shall be maintained under negative air pressure. 
Again, only vectors designed for safety should be used. 
B. Types of Experiments 
The letter published by the Committee on Recombinant DNA 
Molecules in July 1974 requested that the scientific community join the 
Committee in deferring two types of experiments. The letter also advised 
caution regarding a third type of experiment. In the following assessments of 
potential hazards the three original categories are maintained, but with 
some redefinition. 
1) Prokaryotes - Potential biohazards of experiments involving 
genetic exchange among prokaryotic arganisms can in general be accurately 
assessed. 
Experiments involving organisms that normally exchange 
genetic information involve no novel biotypes and pose no hazards that 
cannot be contained by the standard microbiological laboratory techniques 
appropriate for the handling of these organisms. 
Experiments involving the introduction of bacterial genes into 
species in which they have not been found to occur naturally result in novel 
biotypes and so pose increased potential biohazards. Such experiments 
involving genetic determinants affecting pathogenicity for man or other 
species or antibiotic resistance should be undertaken only under conditions 
of moderate or high containment; any large scale industrial, commercial, 
agricultural or other applications should be deferred pending the issuance 
of appropriate official guidelines by national scientific bodies. 
2) Viruses - Experiments employing "low risk" animal viruses 
as vectors to introduce new genetic material into animal cells can be carried 
out under moderate physical containment conditions. 
Experiments involving linkage of viral genomes or genome 
segments to prokaryotic vectors and their introduction into prokaryotic cells 
should be carried out under moderate containment conditions including 
improved vectors. Rigorously purified fragments of the demonstrably 
non-transforming regions of oncogenic viral DNAs or regions of non-oncogenic 
viruses could be attiiched to plasmid DNAs and introduced into E. coli 
under moderate risk conditions with existing vectors. 
Experiments involving high risk viruses should be carried out 
under high containment. 
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