IV. INVESTIGATION OF C. IIIt‘H THERIAE
99
D. Additional phage typing scheme for C. diphtheriae
1. Principles
(a) The additional basic set of typing phages. This set comprises 33 phages
(Fig. 15). It is based upon the principles of both lysogenic and hostrestricted preparations of phages. Twenty-one of the 33 typing phages are
represented by specific host restrictions of the highly virulent lysogenic
phage 951, arising from a C. diphtheriae gravis toxf strain, recorded as
951 “L”. This strain was isolated in 1959 from an outbreak in Romania.
At the time of isolation (CiucS et al., 1960) it consisted of a heterogeneous
cell population, some clones being lysogenic and able to release phages
active against other clones derived from the same strain. Strain 951 “L”
carried a highly virulent phage, endowed with remarkable plasticity
(Maximescu and Saragea, 1969), which made it possible to obtain various
very specific host restrictions in previously untypable C. diphtheriae
strains. These phages, obtained by host restriction, differ in their lytic
activity both from the original phage and from one another. The other
group of 12 phage preparations were obtained, either from C. diphtheriae
biotype intermedius tox- strains (five preparations) or from C. diphtheriae
gravis biotype tox+ strains (seven preparations). Thus, initially, the basic
set of 33 phages was used routinely on 3000 C. diphtheriae strains which
until then had been untypable (Fig. 15). The frequency of typability among
these strains increased step by step with the introduction of new phage
preparations from 32% in 1967 to 73% in 1971.
Afterwards 19 typing phages were selected according to the frequency of
their lytic activity from among the 33 preparations of the initial basic
set (Fig. 16). They were designated by the numbers given them in the
initial series of the 33 preparations. The following phage preparations are
now commonly used in routine work: 1, 2, 6, 7, 8, 9, 10, 11, 13, 15, 17,
19, 20, 21, 23, 25, 26, 29 and 33 (Fig. 16).
If a strain is non-typable by these 19 selected preparations it is subjected
to the whole basic set of 33 phages. Figure 16 presents the origin of the
33 phages and the indicator strain for each. Most indicator strains are
susceptible to only one typing phage but some strains display sensitivity
towards two or more phages. The host restricted phages manifest a strong
activity on the propagating indicator host strain, but occasionally show
low activities (isolated plaques) against other strains.
(b) Additionalphage types. After the application of the basic set to some
3000 C. diphtheriae strains, 14 main additional phage types were selected.
Their phage sensitivity was manifested either by isolated (Fig. 16) lytic
reactions, or by “lytic patterns” as in the “original” phage typing scheme.
These 14 additional phage types were determined by means of the 19
99
D. Additional phage typing scheme for C. diphtheriae
1. Principles
(a) The additional basic set of typing phages. This set comprises 33 phages
(Fig. 15). It is based upon the principles of both lysogenic and hostrestricted preparations of phages. Twenty-one of the 33 typing phages are
represented by specific host restrictions of the highly virulent lysogenic
phage 951, arising from a C. diphtheriae gravis toxf strain, recorded as
951 “L”. This strain was isolated in 1959 from an outbreak in Romania.
At the time of isolation (CiucS et al., 1960) it consisted of a heterogeneous
cell population, some clones being lysogenic and able to release phages
active against other clones derived from the same strain. Strain 951 “L”
carried a highly virulent phage, endowed with remarkable plasticity
(Maximescu and Saragea, 1969), which made it possible to obtain various
very specific host restrictions in previously untypable C. diphtheriae
strains. These phages, obtained by host restriction, differ in their lytic
activity both from the original phage and from one another. The other
group of 12 phage preparations were obtained, either from C. diphtheriae
biotype intermedius tox- strains (five preparations) or from C. diphtheriae
gravis biotype tox+ strains (seven preparations). Thus, initially, the basic
set of 33 phages was used routinely on 3000 C. diphtheriae strains which
until then had been untypable (Fig. 15). The frequency of typability among
these strains increased step by step with the introduction of new phage
preparations from 32% in 1967 to 73% in 1971.
Afterwards 19 typing phages were selected according to the frequency of
their lytic activity from among the 33 preparations of the initial basic
set (Fig. 16). They were designated by the numbers given them in the
initial series of the 33 preparations. The following phage preparations are
now commonly used in routine work: 1, 2, 6, 7, 8, 9, 10, 11, 13, 15, 17,
19, 20, 21, 23, 25, 26, 29 and 33 (Fig. 16).
If a strain is non-typable by these 19 selected preparations it is subjected
to the whole basic set of 33 phages. Figure 16 presents the origin of the
33 phages and the indicator strain for each. Most indicator strains are
susceptible to only one typing phage but some strains display sensitivity
towards two or more phages. The host restricted phages manifest a strong
activity on the propagating indicator host strain, but occasionally show
low activities (isolated plaques) against other strains.
(b) Additionalphage types. After the application of the basic set to some
3000 C. diphtheriae strains, 14 main additional phage types were selected.
Their phage sensitivity was manifested either by isolated (Fig. 16) lytic
reactions, or by “lytic patterns” as in the “original” phage typing scheme.
These 14 additional phage types were determined by means of the 19