RECURRENT ALTERNATION OF PHASE IN SAL. TYPHIMURIUM.
Phase variation is a reversible phenomenon. An alternation of phase occurres

to both directions, from pnase-l to phase=2 and vice versa. However, the study of
phase variation so far has been limited in a few alternative period. Is phase
variation perfectly reversible ? Is there no possibility that an alternation affects
a manifestation of H~antigen at an unremarkable degree ? Such effect may accumulate
in the course of recurrence of the alternation and eventually produce a remarkable
change (for example, a change to a monophasic type.). The experiment reported here

was designed to look into such questions.

Materials and methods.
Two strains of Sal. typhimurium, TM2 i:1,2 and SW1061 ~(i):1,2, were used for
the experiment.
Screening of a clone in an alternative phase was performed as follows:
For TMe,
(1). A penassay broth culture (48 hours, 37C) is streaked onto, EMB-gal plate, and
it is also subcultured to a penassay medium.

the
(2). Antigen type of 20 colonies on, EMB-gal plate was examined by slide agglutination

test.
(3). A colony with an alternate phase is suspended in saline and is streaked onto an

. : . v
BE B-gal plate. If the colony is not obtained, skraak the subculture in Q) opts an
EMB-gal plate and the procedure is repeated.

(4). A single colony is isolated into a penassay broth.

For SW1061,

(1). A penassay broth culture (37¢, 48 hours) is plated with NGA mediun.

(2). A clone of an alternative phase, a colony or a swarm, is suspended in saline
and is streaked onto, EMB-gal plate.

(3). Antigen type of a colony is checked by slide agglutination test, and the
colony is isolated into a penassay media.

(4). When a clone in alternative phase is not obtained in the first NGA plate,

a screenihg procedure is repeated with a subculture.

When the experiment has to be interrupted, the penassay broth culture is kept in

refrigerator in both TM2 and SW1061 test.
Experimental results.

The results are summarized in table 1 and table 2. 17 alternaticow and
35 alternations of phase have been succeeded on TM2 and SW1061 respectively.
The tendency to change the frequency of phase variation has not been recognized
through the alternations. Their motile phases ere as active as the original cultures
of both strains.

The experiment will be continued to compare the intensity of agglutination
by tube agglutination test and to compare the specificity of antigen type by

cross absorption reaction on these clones,
Table 1
RECURRENT ALTERNATION OF PHASE IN TM2 i:1,2.

 

Alternation Antigen Number of Number of Alternation Antigen Number of Number of
number type subcultures alternative number type subcultures alternative
phase per phase per
20 clones 20 clones
1 1,2 1 3 2 i 1 1
3 " 2 2 4 i 3 3
5 " 2 2 6 i 1 2
7 " 2 1 8 i 2 4
9 " 3 3 10 i 1 1
il " e- 2 12 i 3 5
13 " 2 2 14 i 3 2
15 " 3 3 16 i 3 4
17 " 2 18 i

 
table 2
RECURRENT ALTERNATION OF PHASE IN SW1lO61 -(i):1,2.

 

Alternation Number of Wumber of Alternation Number of Number of
number, from phase subcultures clone in total number, from subcultures clone in total
alternative clone phase alternative clone
phase tested phase tested
1 1,2 1 54 C 2 ~-(i) 1 22 141
3 " 1 10 Cc 4 " 2 48 98
5 " 1 21 C 6 " 1 3 79
7 n 1 36 Cc 8 7 1 19 65
9 n 1 2 37 10 " 2 100 < 260 <
ll " Ll 91 400 < 12 " 1 41 200
13 " 2 24 C 14 " 1 8 26
15 7 2 58 130< 16 " 1 32 74
17 " 1 6 Cc 18 " 1 59 148
19 " 1 22 120 < 20 " 1 24 75
él " 1 19 160 < 22 " 2 13 41
23 " 1 10 54 24 " 1 21 216
25 " 1 2 20 26 " 1 16 39
27 " 2 52 C 2é " 1 1 5
29 " 2 11 76 30 " 1 5 29
31 " 1 25 120 < 32 " 1 9 131
33 " 1 46 C 34 " 1 35 119
35 " 1 4 64 36 " 1

 

C: Swarm grew continuously over the surface of a plate.