- 2 - 
Multiple factors define each level in the scale of containment. The 
most important factors, because they contribute most significantly to limiting 
the spread of the recombined plasmids, are biological barriers. r Ihese 
barriers are of two types; fastidious bacterial hosts unable to survive in 
natural environments and non-transmissable vectors designed to grow only in 
specified hosts. A second factor is adherence to good microbiological practices : 
which, to a large measure, can limit the escape of organisms from the experi- '■ 
mental situation. Physical containment, exemplified. by the use of suitable 
hoods, or, where applicable, contained laboratories is an additional factor. 
Further, education and training of all personnel involved in the experiments is 
essential to the effectiveness of all of the above. 
3. Specific Recommendations 
These recommendations reflect the principle that a serious evaluation of 
biohazard potential and the adoption of appropriate biological and physical , 
barriers are integral parts of experiments with recombinant DNA molecules. 
In this section three levels of containment affording increasing protection are 
defined. Then, various types of experiments are evaluated for potential bio- 
hazards and matched with appropriate containment levels. 
U 
A. Types of Containment '■ 
The types of containment are an adaptation of the "NCI Safety 
Standards". 
i 
1) Low-This type of containment involves basic good medical r 
microbiological techniques. The essential factors are wearing lab coats, 
using mechanical pipettes, no eating in the lab, and that sonication and other 
procedures which generate large aerosols should be done in biological safety 
cabinets. 
I 
While existing vectors can be used for this level or containment, 
as safer vectors become available, their use is recommended. 
2) Moderate-Both physical and biological containment enter into 
this containment system. 
The physical containment for moderate risk agents was designed 
for handling moderate risk oncogenic viruses. The main features are that 
transfer operations are to be carried out in biological safety cabinets, gloves 
are worn in addition to lab coats, vacuum lines are protected by filters, and 
negative pressure is maintained in limited access laboratories. 
The physical containment procedures are recognized to provide 
significant but incomplete protection against the accidental spread of biologi- 
cal agents. The potential hazard of moderate risk agents is such that a strong y 
measure of biological containment is needed to ensure their safe handling. 
Therefore, experiments with such agents should only use prokaryotic vectors 
which have been designed with increased safety in mind. Such vectors are 
currently being designed and created, and should be available in the near future 
so that these experiments can proceed. 
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