that lowered physical containment for a given class of experiments 
could increase the number of laboratories where the experiment 
takes place and consequently increase the possible hazard. There 
was particular concern about the need for training in microbiological 
techniques. In response to a question about release of untreated 
air from P3 level laboratories, Dr. Barkley noted that all air 
expelled from inside the biological safety cabinets is filtered 
prior to release while only the air from the normal laboratory 
environment is vented directly. 
Biological Containment 
Dr. Sue Gottesman (NIH) presented the RAC rationale for revisions 
in the area of biological containment. She noted that the use of 
enfeebled hosts and vectors would both limit the potential for sur- 
vival of the host and for transmission of the vector. The best examples 
are the development of a strain of E. c oli K-12 which can 
only survive in a very permissive set of laboratory conditions and 
the creation of vectors with host dependent mutations, such as 
bacteriophage lambda which contains amber mutations and can only 
grow in a supressor host. 
Dr. Gottesman described the HV nomenclature and its application 
as a general host-vector designation. The only HV1 system now in 
existence is EK1, although if other certified hosts are to be used 
experiments should only be conducted at the P2 level with non-pathogenic 
vi 
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