40 
various strains of E^_ coli with humans. For this reason the guidelines 
urge that efforts be made to develop alternate bacterial host-vector sys- 
tems. For this reason also, the guidelines recommend the cautious use of E. 
coli K12 host-vector systems. 
The nature and manner of achieving containment with this system is de- 
scribed in the guidelines, and by reviewing this description in some detail, 
the general principles of biological containment will also become clearer. 
The next slide (3) summarizes some relevant properties of the host 
Slide 3 
E coli Strain K- 12 
Appears to be harmless itself. 
Does not usually colonize normal bowel. 
Does not multiply significantly in alimentary tract. 
Does appear in feces after feeding. 
Has opportunity to transfer vectors to normal flora 
during passage through alimentary tract. 
cells IS. coli K12. The bacteria appears to be harmless itself; it does not 
usually establish itself in the normal bowel, and it does not multiply sig- 
nificantly in the alimentary tract. These facts suggest that accidental 
ingestion of a small number of bacteria by a lab worker would not result 
in extensive spread of a bacterium outside the laboratory. 
The normal situation may be altered when people are either taking 
antibiotics or have certain abnormal digestive conditions, and it is recom- 
mended that such individuals refrain for the duration of the abnormal situ- 
ation from doing experiments with these systems. 
However, while E^_ coli K12 does not establish itself as a growing 
strain in the normal bowel, it does remain alive during its passage through 
the tract. During the passage time, there is the possibility that the 
[181] 
