222
T. BERGAN
200
n
x
0
100
t
n
z
5
I
I
Year
FIG. 3. Incidence of Shigella in Sweden.
majority of the phase I1 strains, although a few phase I strains are also
attacked by the phages. Hammarstrom (1949) mainly used phage XI1 as a
control showing that the bacteria are in phase 11, i.e. suitable for typing.
Phage XI1 was not originally intended for inclusion in the phage type
patterns.
3. Media
(a) Broth for pregrowth of bacterial inocula
Distilled water to
1000 ml
pH adjusted to 7.4 after sterilisation
Nutrient Broth (Difco)
8 g
( b ) Agar for typing, determination of RTD, etc.
Nutrient Broth (Difco)
8 g
Agar (Difco)
15 g
Distilled water to
1000 ml
pH adjusted to 7.4 after sterilisation