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C. Biological Containment Requirements 
Additional safeguards are provided by the use of host cells and 
vectors with demonstrably limited ability to survive in other than 
specially designed laboratory environments. This concept is called 
"biological containment" in the Guidelines. 
Confusion can arise because "biological containment" does not, 
in fact, contain the organisms in the sense that their dispersion from 
the laboratory is controlled. Rather, the term is used to describe 
organisms that, were they to escape the laboratory, would have only a 
slight probability of growing in natural environments. The accidental 
release of a relatively small number of such organisms should not 
lead to an amplification of their number, for the original organisms are 
not likely to survive, and the probability of resulting hazards is thereby 
diminished. 
E. coli K-12 host-vector systems . At present, the system of choice 
for many experiments is the common laboratory bacterium, E. coli 
strain K-12, and independent genetic elements (plasmids and!5acterio- 
phages) known to reside or replicate in this strain. 
The nature and manner of achieving biological containment with this 
system is described in the Guidelines. E. coli K-12 appears to be a 
harmless microorganism. It does not usually establish itself in the 
normal bowel or multiply significantly in the alimentary tract. These 
facts suggest that accidental ingestion of a small number of bacteria 
by a laboratory worker would not result in their extensive spread * 
outside the laboratory. The normal situation may be altered when 
people are either taking antibiotics or have certain abnormal 
digestive conditions, and it is recommended that such individuals 
refrain from work for the duration of the abnormal situation. 
1 1 
While E. coli K-12 does not establish itself as a growing strain 
in normal T5o Weis’, it does remain alive during its passage through 
the tract. Therefore, transfer of plasmid or bacteriophage vectors 
containing foreign DNA from the original E. coli K-12 host to bacteria 
resident in the intestines or bacteria encountered after excretion must 
be considered. For any given host -plasmid combination used in a 
recombinant DNA experiment, it will be necessary to assess the 
possibilities for transfer of the recombinant DNA in order to evaluate 
the degree of biological containment. The available data suggest that 
the probability of transfer can be quite low, depending on the particular 
plasmid used and on the viability of the host cell in natural environments. 
Hence, host -vector systems made up of E. coli K-12 and such plasmids 
appear to have very limited ability to spread recombinant DNA molecules. 
(These systems are discussed in detail in Section VI-C. ) 
