23 
Shiga-like toxin to containment higher than used with naturally occurring 
Shigella dysenteriae ; the E^_ coli K-12 host-vector systems do not have the 
attributes of pathogens. 
Dr. Cchen said there is no reason to expect coli host-vector systems 
expressing the Shiga-like toxin gene would have any greater pathogenic 
potential than Shigella dysenteriae strains ; it would be reasonable to 
handle the Eh_ coli host-vector systems under the sane conditions used to 
handle Shigella dysenteriae . 
Dr. Davis noted that ncmenclature is not as sharp among lower prokaryotic 
organisms as it is among higher organisms. Campylobacter in previous 
editions of Bergey's Manual of Systematic Bacteriology were classified as 
Vibrionaceae . 
Dr. Gottesman moved that RAC accept Dr. O'Brien's proposal as published in 
the August 19, 1985, Federal Register with Campylobacter species considered 
to be Vibrionaceae . Dr. Cchen seconded the motion. 
By a vote of seventeen in favor, none opposed, and no abstentions, the RAC 
adopted the motion. 
Dr. Gottesman explained the working group motion to substitute Shigella 
dysenteriae 60R for E. coli 0157 :H7 in Appendix F-IV-H. Appendix F-IV-H 
specifies that coli K-12 host-vector systems expressing Shiga-like 
toxin may be moved from BL3 to BL2 containment if these systems express no 
more toxin than standard strain 933 E. coli 0157:H7 grown and measured 
under optimal conditions. Substitution of Shigella dysenteriae 60R for 
933 Eh_ coli 0157 :H7 raises by a factor of ten the level of toxin the 
host-vector system may produce and still be removed from BL3 containment. 
E. coli standard strain 0157 :H7 under optimal conditions produces approxi- 
mately i 0 7 cytotoxic doses (CDs) per mg protein in cell lysate; Shigella 
dysenteriae strain 60R produces 10® CDs per mg protein. The issue was 
whether it would be appropriate to specify as a standard a strain expressing 
the maximum amount of toxin expressed under optimal conditions by Shigellae 
found in nature. 
The primary issue for working group members was how safe is safe enough. 
Seme merrbers of the warking group preferred to consider toxin toxicity as 
the primary criterion while other members of the group wished to also 
consider the characteristics of the host-vector system. 
Dr. Davis asked whether the standard should be the behavior of an organism, 
which would vary, rather than an absolute number. Dr. Gottesman said 
designating a bacterial strain as an internal standard is appropriate. An 
internal standard guarantees that individuals who handle the clones well 
[405] 
