APPENDIX E 
appropriate equipment is used. 
The use of bacterial hosts and vectors : Recognizing the relation 
between the host-vector system required by the experiment and the design of 
suitable biological containment, experiments using the same host-vector system 
are grouped together. At present, the system of choice for many experiments 
is the common laboratory bacterium coi i , strain K12, and independent 
genetic elements (plasmids and bacteriophage) known to reside or replicate 
in this strain. There are several factors contributing to this conclusion. 
Strain K12 has been studied extensively and can be readily manioulated for 
recombinant DNA experiments. This same extensive experience and ease of 
manipulation permits modification of E. col i K12 and the vectors by classical 
genetic techniques, for the purpose of establishing biological containment. 
The guidel ines also discuss arguments against the use of E. col i K12, in 
particular the intimate association of various other strains of E. col i with 
humans. For this reason the guidel ines urge that efforts be made to develop 
alternate bacterial host-vector systems. For this reason also, the guidelines 
recommend the cautious use of E. col i K12 host-vector systems. 
The nature and manner of achieving biological containment with this 
system is described in the guidel ines. E. col i K12 appears to be harmless 
itself, it does not usually either establish itself in the normal bowel, or 
multiply significantly in the alimentary tract. These facts suggest that 
accidental injestion of a small number of bacteria by a laboratory worker 
would not result in extensive spread of the 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 recommended that such 
Appendix E — 9 
