Samples from gingival scrapings of dogs were examined for the presence
of CDC Groups EF-4 bacteria. Isolation procedures were performed in 5
% sheep blood agar supplemented with thiostrepton and trimethoprim (10
mg/l). Fifty nine EF-4 strains were isolated from 92% of 49 dogs. Amo
ng the Group EF4 bacteria, the majority of isolates belonged to the ar
ginine-negative (biovar ''b'') Group EF-4 (42 strains recovered in 82%
of dogs). Seventeen arginine-positive strains (biovar ''a'') were rec
overed only from 35% of dogs. The strains were analysed by sodium dode
cyl sulfate-polyacrylamide gel electrophoresis (SDS-PAGE). The analysi
s of electrophoretic protein pattern of these bacteria supported the r
esults of conventional testing, confirmed the distinction between the
biovars ''a'' and ''b'' of Group EF-4 and supported the division of bi
ovar EF-4b into two subgroups of either producing or non-producing aci
d from gluconate.