R.R.B. Russell

ASM JournalsJournal of BacteriologyVol. 177, No. 5Lipoproteins of gram-positive bacteria Free access1 March 1995 Share on Lipoproteins of gram-positive bacteriaAuthors: I C Sutcliffe, R R RussellAuthors Info & AffiliationsDOI: https://doi.org/10.1128/jb.177.5.1123-1128.1995 PDF/EPUB

Attempts to produce resin composite with antibacterial properties by incorporation of an antibacterial agent such as chlorhexidine have been reported, but problems can arise due to release of the inhibitory agent from the composite. Such problems may include toxic effects, influence on mechanical properties, and loss of effectiveness. A new monomer, methacryloyloxydodecylpyridinium bromide (MDPB), was synthesized by combining an antibacterial agent and methacryloyl group. The monomer was incorporated into resin composite to develop a non-releasing antibacterial composite. The ability of composite incorporating MDPB to inhibit growth and plaque accumulation by Streptococcus mutans in vitro was assayed, elution of antibacterial components from the material was investigated, and the influence of incorporation of MDPB on the mechanical properties of composite was studied. Uncured MDPB revealed antibacterial activity against S. mutans and six other species of oral streptococci, with the minimum inhibitory concentration for S. mutans being comparable with that of triclosan. After composite incorporating MDPB was cured, no elution of the antibacterial components was observed from the material, even after 90 days' immersion in water or other solvents. Growth of S. mutans on agar under specimens of MDPB-containing composite was inhibited compared with controls. In a bacterial accumulation study, S. mutans accumulated to a lesser degree on the surface of composite incorporating MDPB (p < 0.05) than on control. Incorporation of MDPB had no significant influence on the mechanical properties of the composite.

An 11-kilobase gene region of Streptococcus mutans has been identified which contains eight contiguous genes involved with the uptake and metabolism of multiple sugars (the msm system). Sequence analysis of this region indicates that several of these genes specify proteins with strong homology to components of periplasmic binding protein-dependent transport systems of Gram-negative bacteria. Additionally, this operon is controlled by a regulatory gene (msmR) that acts as a positive effector. The proteins specified by the structural genes of the msm operon include alpha-galactosidase (aga), a "periplasmic-like" sugar-binding protein (msmE), two membrane proteins (msmF, msmG), sucrose phosphorylase (gtfA), an ATP-binding protein (msmK), and dextran glucosidase (dexB). Insertional inactivation of each of these genes along with uptake data indicate that this system is responsible for the uptake of melibiose, raffinose, and isomaltotriose and the metabolism of melibiose, sucrose, and isomaltosaccharides.

When heat-killed whole organisms of Streptococcus mutans strain Ingbritt (serotype c) were injected into rabbits, antibodies to at least 12 antigens were detectable by crossed immunoelectrophoresis. In contrast, when rabbits were immunized with organisms which had been subjected to extraction with the detergent sodium dodecyl sulphate (SDS), antibodies to only two protein antigens were found. These two proteins (A and B), while existing in a form apparently closely associated with peptidoglycan, could also be recovered from homogenates of whole organisms after sonication and from culture filtrates. Antigenic material was excreted throughout growth. SDS-polyacrylamide gradient gel electrophoresis showed A to have a molecular weight of 29 000, while B had a molecular weight of 190 000. Antigen B was purified to apparent homogeneity as judged by SDS-polyacrylamide gel electrophoresis and isoelectric focusing. All of six strains of serotype c examined produced antigen B. Strains of serotypes e and f also produce antigenically identical proteins and strains of serotypes d and g produce proteins which cross-reacted with antigen B. Antigen B was specifically precipitated by rabbit antiserum to human heart tissue.

The complete nucleotide sequence was determined for the Streptococcus sobrinus MFe28 gtfI gene, which encodes a glucosyltransferase that produces an insoluble glucan product. A single open reading frame encodes a mature glucosyltransferase protein of 1,559 amino acids (Mr, 172,983) and a signal peptide of 38 amino acids. In the C-terminal one-third of the protein there are six repeating units containing 35 amino acids of partial homology and two repeating units containing 48 amino acids of complete homology. The functional role of these repeating units remains to be determined, although truncated forms of glucosyltransferase containing only the first two repeating units of partial homology maintained glucosyltransferase activity and the ability to bind glucan. Regions of homology with alpha-amylase and glycogen phosphorylase were identified in the glucosyltransferase protein and may represent regions involved in functionally similar domains.