Bactericidal activity of human lysozyme, muramidase-inactive lysozyme, and cationic polypeptides against Streptococcus sanguis and Streptococcus faecalis: inhibition by chitin oligosaccharides

Abstract

The bisis of the bactericidal activity of human lysozyme against Streptococcus sanguis was studied. Experiments were designed to evaluate the role of lysozyme muramidase activity in its bactericidal potency. Inactivation of the muramidase activity of lysozyme was achieved by reduction of essential disulfides with dithiothreitol (DTT) or by incubation with the chitin oligosaccharides chitotriose and chitobiose. Muramidaseinactive lysozyme, prepared by reduction with DTT, was equal in bactericidal potency to native lysozyme. Solutions of native chicken egg white lysozyme and human lysozyme exhibited equal bactericidal potency yet differed ca. fourfold with respect to lytic (muramidase) activity. The above results suggested that the bactericidal activity of lysozyme is not dependent upon muramidase activity. Chitotriose and chitobiose were found to inhibit both lytic and bactericidal activities of lysozyme. The bactericidal activity of mnuramidase-inactive lysozyme (reduction with DTT) was also inhibited by chitotriose and chitobiose. Further investigations demonstrated that chitotriose and chitobiose were also potent inhibitors of the bactericidal activity of the cationic homopolypeptides poly-L-arginine and poly-D-lysine. These latter results suggested that the essential bactericidal property of lysozyme was its extreme cationic nature and that some bacterial endogenous activities, inhibitable by chitotriose and chitobiose, were essential for expression of the bactericidal activity of either native or muramidase-inactive lysozyme or of the cationic homopolypeptides. Experiments with Streptococcus faecalis whole cells, cell walls, and crude autolysin preparations implicated endogenous autolytic muramidases as the bacterial targets of chitotriose and chitobiose. The essentially identical responses of S. sanguis and S. faecalis to chitotriose in bactericidal assays with muramidase-inactive lysozyme and polylysine suggested that muramidase-like enzymes exist in S. sanguis and, furthermore, play an essential role in cationic protein-induced loss of viability of the oral microbe. * Corresponding author. some bacteria to oral surfaces. Lysozyme, with a pI > 10.5, is also a rather extreme example of a cationic protein. Cationic proteins are known bactericidal agents against both gram-positive and gram-negative organisms (15, 17, 38, 41, 49, 50). Two modes of bactericidal action are thus available to lysozyme: a muramidase-dependent mode and a cationicdependent mode. The oral streptococci are typically resistant to direct lysis by either human or chicken lysozyme (3, 25, 40). Lysozyme is, however, bactericidal for the major species of oral streptococci (3, 22, 25, 40; N.

Psoriatic scales: a promising source for the isolation of human skin-derived antimicrobial proteins

“…Although the muramidase activity (cleaveage of the glycosidic bond between N-acetylmuramic acid and N-acetyl glucosamine in the bacterial peptidoglycan) of lysozyme has been implicated in its antibacterial activity (especially against Gram-positive bacteria), it has also been shown that the bactericidal potency of lysozyme is not only a result of muramidase activity but also of its cationic and hydrophobic properties [58,59]. Furthermore, it has been demonstrated that the bactericidal effect of lysozyme is synergistically enhanced with hBD-2 and hBD-3 [36,60].…”

Antimicrobial polypeptides

“…Lysozyme is 14 kd enzyme directed against the ␤ 1 3 4 glycosidic bond between N-acetylglucosamine and N-acetylmuramic acid residues that make up peptidoglycan, the cell wall material that gives bacteria their shape. In addition to enzymatic lysis of bacterial cell walls, lysozyme can also kill bacteria by a nonenzymatic mechanism [22]. Although lysozyme is highly active against many Gram-positive species, for example, Bacillus megaterium, Micrococcus lysodeicticus, and many streptococci, it has been described as ineffective against Gram-negative bacteria [23] unless potentiated by certain cofactors (lactoferrin, antibody-complement or hydrogen peroxide-ascorbic acid).…”

Modulation of herpes simplex virus type 1 replication by human salivary secretions

“…These disorders result in the loss of the "acquired pellicles" with a subsequent increase in the number and severity of microbial infections (11,32). These observations are supported by several reports suggesting that the salivary secretions play a role in modulating colonization by opportunistic pathogens (9,10,20) and resident oral fiora (3,8,27,34,42).…”

“…Salivary secretions may interfere with the adhesion of bacteria to oral surfaces to facilitate their clearance from the oral cavity (21,23,30,39,40). In addition, salivary secretions have been shown to contain substances with potential antimicrobial activity that directly affect the growth and viability of pathogenic organisms (8,13,27,35,36,39,41,42). However, the role of salivary secretions in modulation of viral infections in the oral cavity has received little attention.…”