LIVE POLIO IRUS VACCINES

64
Safety-Laboratory Evidence of Attenuation and Safety
TABLE 15. EFFECT OF D,0 ON GROWTH OF CHAT VIRUS IN MONKEY-KIDNEY CELLS AT 40 ° C.
EXP. MEDIUM NUMBER OF PLAQUES PRODUCED IN CULTURES KEPT AT:
NO. 370 C. 400 C.
1 H 2 0 32, 48 0, 0
D 2 0 30, 33 3, 5
2 H 2 0 24, 29 0, 0
D 2 0 19, 21 11, 14
deuterated CHAT virus grown at 400 C. seemed tory, has been developing a temperature marker
to show greater replication of 40 ° in standard test which would be more sensitive than the
medium than progeny of the same virus grown comparative tube.titration tests and less cumberin
deuterated medium at 370 C., where no differ- some and elaborate than the one-cycle growth
ence in plating efficiency between the two systems curve test. In this test, monolayers of monkeywas
observed.
kidney cells are exposed to various concentra-
Experiments are now in progress to determine tions of test viruses, and a certain number of
the mechanism of deuterium use mediated plaque-forming units of the viruses to be tested
through the increased burst size. The results are incubated for different time intervals at 40 °
may perhaps elucidate the nature of some of the C. The plates are then removed from the 400 C.
factors responsible for the genetic markers of incubator and placed in a 37 ° C. incubator. The
the virus. The data should certainly indicate number of plaques is read after an incubation
which part of the virus molecule plays a prom- period of 3-4 days and compared with the numinent
part in the determination of one or another ber of plaques developed on the same systems
marker. kept throughout at 370 C. Table 16 shows data
Finally, since tests for temperature markers related to four strains investigated in this manhave
become important tools for the study of ner. You may observe that only six plaques
polioviruses, Dr. Richard I. Carp, of our labora- were formed by CHAT virus in monolayers kept
TABLE 16.
A MODIFIED TEST FOR TEMPERATURE MARKER
STRAIN HUMAN NUMBER OF PLAQUES ON PLATES KEPT AT 40 ° C.*FOR HOURS:
PASSAGE 0 18 30 42
CHAT 23 6 0 0
CHAT Q-1 1 4 0 1 o0
SICKLE 18 48 55 49
MAHONEY 18 71 92
* And then incubated at 37 ° C for 3-4 days.