Ruminococcus flavefaciens adhered instantly to cellulose, while Fibrobacter succinogenes had the highest percentage of adherent cells after about 25 min of contact between bacteria and cellulose. Adhesion of R. flavefaciens was unaffected by high concentrations of sugars (5%), temperature, pH, oxygen, metabolic inhibitors, and lack of Na+. In contrast, the attachment was affected by the removal of divalent cations (Mg2+ and Ca2+), the presence of cellulose derivatives (methylcellulose and hydroxyethylcellulose), and cystine. Adhesion of F. succinogenes was sensitive to low and high temperatures, high concentrations of glucose and cellobiose (5%), hydroxyethylcellulose (0.1%), redox potential, pH, lack of monovalent cations, and the presence of an inhibitor of membrane ATPases or lasalocid and monensin. Cells of F. succinogenes heated at 100°C no longer were adherent. On the other hand, adhesion was insensitive to the lack of divalent cations (Mg2+ and Ca2+), the presence of 2,4-dinitrophenol, tetrachlorosalicylanilide, or inhibitors of the electron transfer chains. Adhesion of F. succinogenes seems to be related to the metabolic functions of the cell. External proteins and/or cellulases themselves might play a part in the attachment process. Several mechanisms are probably involved in the adhesion of R. flavefaciens, the main one being the interaction between the large glycocalyx and the divalent cations Ca2' and Mg2+. Hydrophobic bonds and enzymes may also be involved.

Lysozyme, lactoperoxidase and salivary peroxidase inhibit the metabolism and growth of mutans streptococci, but any possible effects on the adherence of these bacteria are unknown. In this study the effects of lysozyme and lactoperoxidase on the adhesion of ³H-labelled Streptococcus mutans (NCTC 10449, serotype c strain) to saliva-coated hydroxyapatite were studied at pH 5.0 and 7.0. Human whole saliva was either lysozyme-depleted and centrifuged, or sterilized and dialysed to achieve no detectable lysozyme and peroxidase activities; this modified saliva was used to form experimental pellicles. The incorporation of lysozyme (50–200 μg/ml) to the pellicle caused a significant (p < 0.01) reduction in the adherence of S. mutans without any loss of bacterial viability. Pretreatment of either saliva-coated apatite or S. mutans cells with lysozyme did not change the results but lysozyme bound more readily to bacteria than to the experimental pellicles. Also, lactoperoxidase (10–200 μg/ml) reduced significantly (p < 0.001) the adherence of S. mutans but, in contrast to lysozyme, in a dose-dependent way. The strongest inhibition of adhesion was found when both saliva-coated apatite and bacteria were pretreated with lactoperoxidase. This enzyme bound to experimental pellicles in preference to streptococci. A non-specific protein control, albumin, did not block the inhibition by lysozyme or lactoperoxidase. The inhibition of adherence of a serotype c strain of S. mutans to saliva-coated hydroxyapatite is a novel antibacterial mechanism for both lysozyme and lactoperoxidase.

Fluoride (F^-) ions at concentrations present in vivo at the plaque/enamel interface (0.05–10 mM) inhibited the 4activities of lactoperoxidase (LP), myeloperoxidase (MP) and total salivary peroxidase (TSP) in a pH- and dose-dependent way. The inhibition was observed only at pH ≤ 6.5 and with F concentrations ≥ 0.1 mM. At pH 5.5 LP activity was inhibited by 85% and MP by 34% with 10 mM F^-. TSP activity was also inhibited only at low pH (5.5) by approximately 25%. Furthermore, the generation of the actual antimicrobial agent in vivo, hypothiocyanite (HOSCN/OSCN), of the oral peroxidase systems was inhibited by F^-, again at low pH (5.0–5.5) both in buffer (by 45%) and in saliva (by 15%). This inhibition was observed only with the highest F^- concentrations studied (5–10 mM). Fluoridated toothpaste (with 0.10 or 0.14% F) mixed with saliva did not inhibit TSP or HOSCN/OSCN generation. This may have been due to the ‘buffering’ effect of toothpaste which did not allow salivary pH to drop below 5.9. We conclude that the F^- ions in acidic fluoride products, e.g. in gels or varnishes (but not in toothpastes), may have the potential to locally inhibit the generation of a nonimmune host defense factor, HOSCN/OSCN/SCN produced by oral peroxidase systems. The possible clinical significance of this finding remains to be shown.

Summary. The effect of some physico-chemical factors on the attachment to cellulose was studied in 2 cellulolytic rumen bacteria, Ruminococcus flavefaciens and Bacteroides succinogenes. The

The adhesion of 3H-labelled Streptococcus mutans (serotype c) cells to spheroidal hydroxyapatite (HA) beads was studied by precoating HA with whole saliva with or without the presence of human lactoferrin (LF). Treatment of HA with LF-free saliva prevented the streptococcal adhesion more strongly than treatment with buffer alone. However, supplementation of LF-free saliva by iron-free LF (apo LF), or partly or totally Fe"-saturated LF (200 mg/l), significantly enhanced (P<0.001) the inhibition. No notable differences existed between the various forms of LF. The inhibition of bacterial adherence was dose dependent with respect to the amount of LF bound to saliva-coated HA (SHA), suggesting a non-specific protein blockage. Significant (P<0.001) inhibition was observed with apo LF concentration as low as 10 mg/l. LF-mediated inhibition of the adherence of S. mutans, serotype c, to SHA is obviously non-specific, antibacterial function for this innate defence protein which is present in human saliva, gingival crevicular fluid and also as an integral part of the acquired salivary pellicle in vivo.