Further studies on immunoglobulin G- and albumin-binding properties of streptococci of serological group L

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.

Binding properties of Streptococcus suis for immunoglobulin G and other plasma proteins

Immunoglobulin G (IgG) binding proteins on the surface of Streptococcus suis could be readily detected by direct cultivation of the bacteria on nitrocellulose membranes and subsequent treatment of the membranes with human IgG. Among the 75 S. suis isolates tested two cultures (S. suis P43, S. suis P143) caused a blue colouration of the membranes indicating IgG binding activities. The IgG binding proteins could be solubilized by heat treatment of the bacteria at an acid pH and also by mutanolysin treatment. Western blot analysis revealed numerous protein bands with IgG binding activities. The IgG binding proteins were also released into the culture supernatant of the bacteria. This could be detected for 51 of the 75 S. suis using a microfiltration assay. In binding studies with 125I-IgG S. suis P43 and S. suis P143 but none of the other S. suis isolates showed a significant binding of the protein. These two cultures additionally bound 125I-albumin, 125I-alpha 2-macroglobulin and 125I-fibrinogen all from humans but not 125I-chicken IgG or 125I-human haptoglobin 2-1. The binding profiles of the two S. suis cultures tested indicate a close relation of these binding proteins with streptococcal protein G.