VI. IDENTIFICATION OF ACTINOM YCES AND ARACHNIA
305
A . viscosus strains are divided into two serotypes as shown in Table VIII.
Gerencser and Slack (1969) showed that rodent strains (serotype 1) were
serologically distinct from human isolates (serotype 2). Both serotypes
cross-reacted with A . naeslundii and to a lesser extent with A . israelii but
had only a one-way cross-reaction with each other in which A . viscosus
serotype 1 conjugate stained A . viscosus serotype 2 cells. The two serological types of A . viscosus and their cross-reactions have been confirmed by
Bellack and Jordan (1972) and by Holmberg and Forsum (1973). Like the
other species, antigenic variation can be demonstrated in strains of A.
viscosus serotype 2. Georg et al. (1972) studied A . viscosus isolates from
dogs, pigs and a goat. The FA reactions of these strains were not identical
to those of either rodent or human strains although high-titred crossreactions occurred. This suggests that further serotypes may occur among
animal strains. I n our collection of isolates from human dental plaque,
there are strains of A . viscosus which stain poorly or not at all with available
conjugates, also suggesting additional serotypes among human strains.
Arachnia propionica can be divided into two serotypes. These serotypes
were described by Gerencser and Slack (1967) with only a single strain
(WVU 346) representing serotype 2. The serotypes cross-react at low
titres in FA tests but the sera are easily made type specific by dilution or
preferably by absorption. Brock et al. (1973) confirmed the existence of
two serotypes in a study of 11 cases of actinomycosis due to Arachnia
propionica. Three of the 11 strains isolated in this study belonged to
serotype 2. Genetic data from an extensive study of Propionibacterium and
Arachnia by Johnson and Cummins (1972) has raised a question concerning
the serotype 2 strains of Arachnia propionica. They found no DNA homology between Arachnia propionica serotype 1 strains and strain WVU 346
(VPI 5067) but a high degree of homology was found between serotype 1
strains. On the other hand, in the recent numerical taxonomy study of
Holmberg and Nord (1975), strain WVU 346 clustered with other strains
of Arachnia propionica on a phenetic basis.
2. Absorbed conjugates
The cross-reactions previously discussed are those which occur when
unabsorbed conjugates are tested at varying dilutions. Many of the crossreactions are eliminated by simple dilution of the conjugate to its working
titre. However, to ensure species specificity and to avoid missing the
occasional strain which reacts with a conjugate at low dilutions only,
absorbed conjugates are generally used for direct staining of clinical
specimens and for confirming the identification of pure cultures. Absorbed
conjugates are prepared so that there are no interspecies cross-reactions.
Additional absorbed conjugates are needed for serotyping.
11
305
A . viscosus strains are divided into two serotypes as shown in Table VIII.
Gerencser and Slack (1969) showed that rodent strains (serotype 1) were
serologically distinct from human isolates (serotype 2). Both serotypes
cross-reacted with A . naeslundii and to a lesser extent with A . israelii but
had only a one-way cross-reaction with each other in which A . viscosus
serotype 1 conjugate stained A . viscosus serotype 2 cells. The two serological types of A . viscosus and their cross-reactions have been confirmed by
Bellack and Jordan (1972) and by Holmberg and Forsum (1973). Like the
other species, antigenic variation can be demonstrated in strains of A.
viscosus serotype 2. Georg et al. (1972) studied A . viscosus isolates from
dogs, pigs and a goat. The FA reactions of these strains were not identical
to those of either rodent or human strains although high-titred crossreactions occurred. This suggests that further serotypes may occur among
animal strains. I n our collection of isolates from human dental plaque,
there are strains of A . viscosus which stain poorly or not at all with available
conjugates, also suggesting additional serotypes among human strains.
Arachnia propionica can be divided into two serotypes. These serotypes
were described by Gerencser and Slack (1967) with only a single strain
(WVU 346) representing serotype 2. The serotypes cross-react at low
titres in FA tests but the sera are easily made type specific by dilution or
preferably by absorption. Brock et al. (1973) confirmed the existence of
two serotypes in a study of 11 cases of actinomycosis due to Arachnia
propionica. Three of the 11 strains isolated in this study belonged to
serotype 2. Genetic data from an extensive study of Propionibacterium and
Arachnia by Johnson and Cummins (1972) has raised a question concerning
the serotype 2 strains of Arachnia propionica. They found no DNA homology between Arachnia propionica serotype 1 strains and strain WVU 346
(VPI 5067) but a high degree of homology was found between serotype 1
strains. On the other hand, in the recent numerical taxonomy study of
Holmberg and Nord (1975), strain WVU 346 clustered with other strains
of Arachnia propionica on a phenetic basis.
2. Absorbed conjugates
The cross-reactions previously discussed are those which occur when
unabsorbed conjugates are tested at varying dilutions. Many of the crossreactions are eliminated by simple dilution of the conjugate to its working
titre. However, to ensure species specificity and to avoid missing the
occasional strain which reacts with a conjugate at low dilutions only,
absorbed conjugates are generally used for direct staining of clinical
specimens and for confirming the identification of pure cultures. Absorbed
conjugates are prepared so that there are no interspecies cross-reactions.
Additional absorbed conjugates are needed for serotyping.
11