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Slide 2 
DESCRIPTION OF POTENTIAL EK2 HOST 
Strain x!776 and its derivative, xl876, possess the following 
traits: 
1. Mutations conferring important properties are due to 
deletions of genetic information 
2. Require d iam i nop imel i c acid (needed for cell wall 
biosynthesis) and thymidine (needed for DNA synthesis) 
3. Have generation times 2-4 times longer than wild-type 
E^. col i strains 
4. Are sensitive to bile salts 
5- Are very sensitive to ultraviolet light 
6. Are more sensitive to many antibiotics, drugs, and 
detergents than parental strain from which derived 
7- Cannot be productively infected with most known E^. col i 
transducing phages 
8. Are unable to inherit most conjugative plasmid types 
and are defective in inheriting other conjugative 
plasmid types 
thymidine, which is needed for DNA synthesis, and also mutations that do 
not permit the production of mucopolysaccharides, which permit wall-less 
bacteria to survive in nature; three, have generation times two to four 
times longer than wild-type E. coli strains, and thus will not permit com- 
petition with robust strains in nature; four, are sensitive to biosalts, 
thus precluding survival in the intestine; five, are very sensitive to 
ultra-violet light; six, are more sensitive to many antibiotics, drugs and 
detergents than the parental strain from which derived; seven, cannot be 
productively infected with most known _E^_ coli transducing phages which could 
act to transmit genetic information to other strains in nature; and eight, 
are unable to inherit most conjugative plasmid types and are defective in 
inheriting others under optimal laboratory conditions for detecting these 
events. 
Next slide (3), please. 
In addition to the traits listed on the previous slide, these strains: 
one, cannot survive passage through the intestinal tracts of rats, when 10 
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