which stipulate that "Individuals receiving antibiotics should 
not work with prokaryotic host-vestor systems during therapy 
nor for seven days after." (42 F.R. 49604). Since commonly 
used vectors are plasmids coding for antibiotic resistance, 
those workers undergoing antibiotic therapy would be good 
potential carriers for bacteria containing recombinant DNA. 
This has been well documented in animals and humans. For 
example, Timoney reported that 88% of 249 strains of S_. tymphimurium 
isolated from diseased animals in New York State from 1973 to 
1976 were resistant to six commonly used antibiotics. Ninety-one 
percent of these strains possessed transf errable resistance.^/ 
Dr. Levy reported at the Falmouth conference that resistant 
strains proliferate in farm inhabitants (including humans) 
upon incorporation of antibiotics into animal feeds. 
(F: 688-690) Resistant strains can be passed back and forth 
between animals and humans. Dr • Levy concluded that: 
... we must . , . bear in mind that antibiotic 
usage is widespread and that the drugs themselves 
are major selective forces for resistant 
organisms. Thus, if a recombinant vector with 
a resistance marker were to escape into the 
environment, it would then have a better chance 
for survival, an undesirable feature. 
Therefore, antibiotic markers of commonly prescribed 
drugs should not be used on vectors for recombinant 
DNA research. (F: 690) . 
23 / J. F. Timoney, Journal of Infectious Diseases , 137 (1978), 67. 
24/ s. B. Levy, Nature , 260 (1976), 40-42. 
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