23 
v ’'_zse as ''leads packed with DM; when necessary and under 
special It controlled conditions , t'^se heads could be node 
infective b- add ing tail preparations . An additional safety 
~ac~r in thus real-men vs t'ie extreme tnstabtvtty oj tne 
heads, unless they are stored in lOnM putrescine , a con- 
ditio n easy to obtain in the laboratory but not in nature. 
The propagation of the escaping phage in nature could 
mat her be blocked bn adding various conditional 'nutations 
wkich would permit growth only ; under special laboratory 
conditions or in a special remissive laboratory host 
with suppressor or ore - tree ' tot, drab, root ', 'nutations. .An 
additional safer, feature would be the use of an r~ m~ hsdS) 
laboratory host, which produces phage with unmodified Zb. A 
which should be restricted in r + m + bacteria that are probably 
prevalent in nature . Zhe likelihood of recombination between 
tie \ vector ad larbdoid prophages which are present in some 
J. jjT ^ strains right be reduced by elimination of the Red 
—unction and the presence of tie recorbinatium-reducinq Gam 
function together with mutations contributing to the high 
lethality of the \ ghege . However, these second-order pre- 
cautions might not be relevant if the stability and infectivity 
of the escaping \ particles are reduced by special mutations 
or by propagating te highly unstable heads. 
Ze spivs multi 
os ore to ry : vosts. 
pie mutations in the phage vectors and 
the yield of phage particles under suitable 
' r: ' nditions -I “ 
'tides, /ml) 
[ 94 ] 
