Comparative studies on streptococci of serological group G isolated from various origins.

The streptococcal cultures used in the present study were isolated from dogs, bovines and humans and could be classified into Lancefield's serological group G. Most of the group G streptococci grew in fluid media as granular sediment with clear supernatant and formed compact colonies in soft agar. The majority of the group G streptococci from dogs and bovines displayed CAMP-like synergistic haemolytic activities on sheep blood agar, fermented lactose and salicin and produced the enzyme alpha-D-galactosidase. The group G streptococci from humans mainly fermented trehalose and produced the enzyme beta-D-glucuronidase. In addition, some of the group G streptococci reacted with type antigen X and R and two cultures with M6 specific antiserum. A positive opacity factor reaction could be observed with few group G streptococci isolated from dogs and bovines, but not with those from humans. In binding studies with 125I-labelled plasma proteins most of the cultures interacted with 125I-immunoglobulin G and 125I-albumin. Binding of 125I-IgG was more pronounced among group G streptococci isolated from humans. The determination of antibiotic susceptibility revealed that most of the group G streptococci were susceptible to bacitracin, cefoxitin, clindamycin, erythromycin, gentamicin, penicillin and sulfamethoxazole-trimethoprim. Some of the cultures were resistant to minocycline, neomycin and tetracycline. All this data clearly distinguished group G streptococci isolated from animals and humans and could additionally be used for individual characterization of this microorganism. This might be useful in epidemiological aspects and contribute to understanding infections caused by these bacteria.