The role of fibronectin in the streptococcal adhesion process

The work shows that fibronectin obtained from human plasma is capable of binding with streptococci of different groups with almost equal effectiveness. Fibronectin bound to bacterial cells inhibits the adhesion of group A streptococci onto vaginal cells, but it produces no effect on the adhesion of group B streptococci. The binding constant of fibronectin 125I is equal to 10(6) -M-1, which indicates that the level of the specificity of interaction is not sufficiently high.     

Adherence to epithelial cells and ultrastructure of fosfomycin-resistant mutants of group A streptococci

Adherence of three strains of group A streptococci and their fosfomycin-resistant mutants to HEp-2 tissue culture cells was compared with some cell-surface characteristics, i.e. ultrastructure and hydrophobicity. Among Fosr mutants, both well-adhering and weakly adhering mutants were found. Clonal analysis of the mutants proved their greater stability in the adherence. Well-adhering parent strains of streptococci and Fosr mutants exhibited surface fibrillae in contrast to weakly adhering Fosr mutants which were devoid of fibrillae or contined fibrillae of lower electron density. Decrease of adherence of Fosr mutants of two strains was accompanied by a decrease of their hydrophobicity.     

Sequencing of genes within the vir regulon of Streptococcus pyogenes type M15 — an opacity factor-positive serotype with low opacity factor expression

Major virulence determinants of group A streptococci, such as M-protein, immunoglobulin Fc-receptors (FcRA, EmmL) and C5a peptidase, appear to be genetically co-regulated, their genes being located within a vir regulon. We studied the organization of these genes in a group A, type M15 strain of Streptococcus pyogenes, previously defined as OF^?, by hybridization analysis of chromosomal DNA and of an S. pyogenes gene library in Escherichia coli, and by gene sequencing. Within the vir regulon, in addition to the virR and scpA genes, three so-called emm-related genes were found: fcrA, emmL and enn. Whereas IgG Fc-binding proteins were encoded by fcrA and emmL, the product of enn was not identified. The presence of three emm-related genes in this region is reminescent of vir regulon organization in OF⁺ rather than OF^? strains as earlier defined by others. Furthermore, analysis of the deduced product of the emmL gene showed deletions and amino acid substitutions within the PGTS-rich domain and membrane anchor, which thus resembles corresponding products of OF⁺ rather than OF^? strains. In view of these findings, the opacity factor (OF) activity of the strain was tested using growth supernatant, with negative outcome. However, a concentrated SDS cell extract revealed definite OF activity. One of two other type M15 reference strains also showed definite OF activity in SDS extracts. We therefore propose that type M15 strains belong to the OF⁺ category but often show low levels of expression of OF.     

Isolation and study of fosfomycin-resistant mutants of group A and B streptococci

Eighty-nine fosfomycin-resistant mutants of group A and B streptococci were isolated. The mutants differed essentially from the parent strains in cell-wall characteristics, such as morphology of cocci and chains, sensitivity to detergents and hydrophobic properties. At the same time, the recipient activity of the investigated mutants was not changed. It is supposed that resistance of mutants to fosfomycin is connected with a transport block of glycerol 3-phosphate--important lipoteichoic acid (LTA) structural component. Fosr mutants can be useful for experimental examination of Beachey's hypothesis about the importance of LTA or its complex with the M protein for adhesion.     

Factors and genetics of pathogenicity of group B Streptococci

In this review data on the pathogenicity factors of streptococci and their genetic control are presented. Attention is paid mainly to protein antigens alpha and beta, C5a peptidase, CAMP factor, R, Rib and X proteins. The problems of making the genetic and physical charts of the genome of group B streptococci, the genetic regulation of the synthesis of pathogenicity factors and the specific features of the damaging action of the infective agent are discussed.     

Protective properties of certain external proteins of group B streptococci

On the basis of genes, which control synthesis of externally localized proteins of group B streptococci (bac and scaAB), recombinant polypeptides P6 and ScaAB were obtained. Data on protective activity of these polypeptides during experimental infection of immunized mice as well as in opsonophagocytic test on cultivated peritoneal macrophages are presented. It has been shown that protective effect of specific antibodies to P6 was dependent from intensity of immune response. Titer of specific IgG to P6 equal 1:25000 was protective for mice during challenge with LD50. During sublethal challenge level of humoral immunity determined both rate of microorganism elimination and degree of decrease of concentration of streptococci in the spleen. Recombinant polypeptide ScaAB also had marked protective activity and protective titer ScaAB-specific IgG was significantly lower compared with the first polypeptide (1:1600). It has been established that both types of antibodies have opsonizing activity against different strains of group B streptococci. Opsonizing properties of antibodies to P6 were restricted to Bac protein-producing streptococci whereas specificity of antibodies to ScaAB was not restricted by type and group borders. Opsonization of both group B and group A streptococci was revealed. It has been established that protective efficacy mediated by antibodies was dependent not only from their opsonizing characteristics but also from availability of protein antigens, which under certain conditions can be shielded by capsular polysaccharide. It has been assumed that vaccine preparation developed on the basis of polypeptides P6 and ScaAB is promising for further research.     

Experimental evaluation of recombinant polypeptides as Streptococcus Group B vaccine

Recombinant polypeptides corresponding to the conservative N-terminal area of Bac surface protein of group B streptococci (GBS) and having the human IgA binding-site were obtained and evaluated in terms of Immunogenic and protective properties. GBS strain 219, serotype 1 bc, served as the source of chromosomal DNA used for cloning. Three polypeptides P1, P5 and P6 were constructed. Polypeptides P1 and P5 with a molecular weight of 22 kD were coded by practically identical DNA fragments (685 nucleotide pairs) and differed in two aminoacids In their central part. Polypeptide P6 had a molecular weight of 35 kD, The fragment of recombinant Bac protein with a molecular weight of 35 kD was found to have protective properties: when used for the subcutaneous immunization of animals, it stimulated the development of immune response capable, in case of challenge, to induce accelerated elimination of streptococci and the prevention of the mice death. Recombinant fragment P6 of GBS protein Bac may be regarded as a candidate for inclusion into GBS-specific vaccine.     

Distribution of type-specific antibodies to streptococcal lipoproteinase based on population screening data

In the serum samples obtained from residents of the Todzhinsky district in the Tuva Autonomous Soviet Socialist Republic antibodies to 12 out of 15 studied types of group A streptococcal lipoproteinases (OF-factor) were detected, with the prevalence of types 2, 4, 22, 25, 48, and 60, their incidence in the population constituting 34%. Antibodies to OF-antigens 58, 62, and 63 were not detected. The distribution of OF-antibodies was found to vary with sex, occurring in females 1.5 times more frequently than in males, and with age, accumulating in subjects aged 21-30 and 31-40. The distribution of antibodies to different OF serotypes did not depend on the blood serum streptolysin O titers.