In vitro and in vivo studies of cellular lysis of oral bacteria by a lysozyme-protease-inorganic monovalent anion antibacterial system

Targeted immobilisation of lysozyme in the enamel pellicle from different solutions

Mouthwashes containing protective enzymes are required especially for patients suffering from xerostomia. The present study aimed to investigate the possibilities of modulating the immobilisation of lysozyme in the in situ pellicle layer. In situ formed pellicles were incubated in vitro for 10 min with various enzymatic buffer solutions containing lysozyme and additive enzymes such as transglutaminase or trypsin as well as polyphenolic compounds (cistus tea). After the rinses, the pellicle samples were incubated in collected whole saliva or in desorption solutions for 0, 20 and 40 min and the enzyme activities were measured. Furthermore, accumulation of lysozyme in the pellicle was visualised in ultrathin sections of the pellicle using the gold immunolabelling technique and transmission electron microscopy. Hen egg white lysozyme was accumulated in the in situ pellicle tenaciously. Up to 2.8-fold higher activities than in controls were observed. The addition of transglutaminase did not enhance the immobilisation of lysozyme activity, whereas the polyphenolic compound had no adverse effect. Accumulation of lysozyme in the acquired pellicle was confirmed by gold immunolabelling. Targeted and tenacious immobilisation of lysozyme in the acquired pellicle is possible. Poylphenolic compounds might be a relevant additive for mouthwashes containing lysozyme.

Fluorescence microscopic visualization and quantification of initial bacterial colonization on enamel in situ

OBJECTIVE

The acquired salivary pellicle has been defined as proteinaceous film free of bacteria. However, due to the large numbers of microorganisms existent in the oral fluids, it is conceivable that adherent bacteria are already present in the initial pellicle. The aim of this in situ study was to visualize and to quantify these bacteria.

DESIGN

Initial biofilm formation was performed on bovine enamel slabs mounted buccally on individual splints and carried in situ by six subjects for 3, 30 and 120 min, respectively. After intraoral exposure, the slabs were rinsed with saline solution and the adherent bacteria were investigated with the following fluorescence microscopic methods: staining with 4',6-diamidino-2-phenylindole (DAPI), staining of vital and nonvital bacteria with fluoresceinediacetate and ethidiumbromide (live/dead staining) and fluorescence in situ hybridization (FISH) of eubacteria and streptococci, respectively. In addition, determination of colony forming units after ultrasonically induced detachment of bacteria was performed.

RESULTS

With all the methods, bacteria were detected in the initial in situ biofilm irrespective of the formation time. The numbers of bacteria revealed high intraindividual and interindividual variability and the microorganisms were distributed randomly in small aggregates. The results of the epifluorescence microscopic techniques corresponded well. The mean number of adherent bacteria detected was in the range of 10-20x10(4)cm(-2).

CONCLUSION

Already after 3 min, adherent bacteria are present in the initial pellicle. For the first time, DAPI-staining as well as FISH have proven success for visualization of initial intraoral colonization of enamel specimens.

Susceptibility of Candida dubliniensis to salivary histatin 3

Candida dubliniensis is a recently described Candida species associated with oral candidiasis in human immunodeficiency virus (HIV)-infected patients and patients with AIDS. The majority of C. dubliniensis clinical isolates tested to date are susceptible to the commonly used antifungal drugs, including fluconazole, ketoconazole, itraconazole, and amphotericin B. However, the appearance of fluconazole-resistant C. dubliniensis strains in this patient group is increasing. Histatins are a family of basic histidine-rich proteins present in human saliva which have therapeutic potential in the treatment of oral candidiasis. The mechanism of action of histatin is distinct from that of commonly used azole and polyene drugs. Characterization of the antifungal activity of histatin has mainly been carried out using C. albicans but it is also effective in killing C. glabrata and C. krusei. Here we report that C. dubliniensis is also susceptible to killing by histatin 3. The concentration of histatin 3 giving 50% killing (the IC(50) value) ranged from 0.043 to 0.196 mg/ml among different strains of C. dubliniensis. The least-susceptible C. dubliniensis strain, P9224, was found to internalize histatin at a lower rate than the C. albicans reference strain CA132A. The dissociation constant (K(d)) for the least-susceptible strain (C. dubliniensis 9224) was ninefold higher than that for the C. albicans reference strain. These results suggest that histatin 3 may have potential as an effective antifungal agent, particularly in the treatment of oral candidiasis in HIV-infected patients and patients with AIDS in which resistance to the commonly used antifungal drug fluconazole has emerged.

Efeito de um dentifrício fluoretado contendo bicarbonato de sódio na contagem de estreptococos do grupo mutans, acidogenicidade e composição da placa dental

Avaliou-se o efeito de um dentifrício contendo bicarbonato de sódio na contagem de estreptococos do grupo mutans (EM), acidogenicidade e composição da placa dental. Vinte e três voluntários escovaram os dentes 3 vezes ao dia, com formulações fluoretadas (1.500 ppm F), contendo, ou sílica (SÍLICA), ou carbonato de cálcio (CARBONATO), ou carbonato de cálcio mais bicarbonato de sódio (CARB/BICAR), num delineamento duplo cego cruzado, com 3 etapas de 30 dias. No 28º dia, 8 a 12 horas após a última escovação, foi realizada a contagem de estreptococos do grupo mutans na saliva (EMS). No 30º dia (após 2 dias, nos quais os voluntários bochecharam 3 vezes/dia uma suspensão do dentifrício em água, e 6 vezes/dia sacarose a 10%), analisou-se na placa dental, após 10 a 12 horas do último bochecho de dentifrício: a) contagem de mutans (EMP); b) polissacarídeos álcali solúveis (PSA); c) flúor solúvel em ácido (FSA); d) pH no tempo zero (T0), após 5 minutos de bochecho com sacarose (T5), calculando-se o <FONT FACE="Symbol">D</font>pH (T0-T5). Os resultados (média + erro padrão) para SÍLICA, CARBONATO e CARB/BICAR foram respectivamente:1) EMS (x106 UFC/ml saliva) = 11,43 + 7,62 A; 2,33 + 1,04 A; 2,07 + 1,10 A; 2) EMP (x106 UFC/mg placa) = 0,099 + 0,095 A; 0,027 + 0,018 A; 0,007 + 0,003 A; 3) PSA (<FONT FACE="Symbol">m</font>g/mg placa) = 6,89 + 0,62 AC; 8,46 + 0,80 AB; 6,11 + 0,59 C; 4) FSA ((<FONT FACE="Symbol">m</font>g/g placa) = 36,67 + 10,10 A; 48,12 + 19,23 A; 52,21 + 15,12 A; 5) T0 = 6,72 + 0,12 A; 6,88 + 0,13 A; 6,65 + 0,11 A; 6) T5 = 5,61 + 0,13 A; 5,71 + 0,13 A; 5,70 + 0,12 A; 7) <FONT FACE="Symbol">D</font>pH = 1,12 + 0,11 A; 1,17 + 0,11 A; 0,95 + 0,10 A, sendo que médias seguidas por letras distintas diferem entre si ao nível de 5% de significância. Os resultados demonstram que, embora o dentifrício contendo bicarbonato de sódio tenha apresentado, coletivamente, uma tendência a influenciar positivamente nos diversos fatores relacionados à cárie dental, não diferiu significantemente dos dentifrícios contendo carbonato de cálcio ou sílica como abrasivo.

Bacterial-protein interactions in the oral cavity

Bacteria in the oral cavity must interact with salivary proteins if they are to survive. Such interactions can take several forms, either providing nutrients, a means of adhesion to surfaces, or resulting in aggregation or killing and, therefore, clearance of organisms. Recent work has provided an insight into the mechanisms of some of these bacterial-protein interactions, revealing complexity and diversity. For example, the interaction between a putative Streptococcus mutans adhesin, P1 (B, I/II, etc.), and a parotid glycoprotein results in adhesion when it occurs at a surface or aggregation when in solution, and different domains of P1 appear to be involved in the two processes. An alternative strategy is employed by Actinomyces viscosus, which interacts, via its type-1 fimbriae, with a proline-rich salivary protein; however, this interaction occurs only when the PRP is adsorbed to a surface. A. viscosus takes advantage of a conformational change in the PRP when it becomes surface-bound, which exposes a cryptic part of the molecule. A third, and intriguing, type of interaction is seen between various streptococci and salivary amylase. This does not result in either adherence or aggregation but provides organisms with the ability to utilize starch breakdown products for metabolism. An understanding of the mechanisms involved in bacterial-protein interactions could conceivably lead to novel methods for controlling specific pathogens, but the systems operating in the mouth are numerous, complex, and diverse.

The effects of lactoferrin on gram-negative bacteria

Lactoferrin is an iron-binding protein found in human mucosal secretions as well as the specific granules of polymorphonuclear leukocytes. A variety of functions have been ascribed to the protein, and it appears to contribute to antimicrobial host defense. In particular, it has been shown to have direct effects on pathogenic microorganisms including bacteriostasis and the induction of microbial iron uptake systems. Still its overall physiologic role remains to be defined. It has appeared logical that antimicrobial activity of the protein arises from sequestration of environmental iron thereby causing nutritional deprivation in susceptible organisms. This argument is buttressed by the finding that selected highly virulent pathogens have evolved techniques to subvert this effect and use the protein as an iron source. However, recent observations indicate that the protein has additional properties that contribute to host defense. Work by several groups has shown that the protein synergistically interacts with immunoglobins, complement, and neutrophil cationic proteins against Gram-negative bacteria. Further, both the whole protein and a cationic N-terminus peptide fragment directly damage the outer membrane of Gram-negative bacteria suggesting a mechanism for the supplemental effects. This review will summarize these diverse observations with a consideration of how the in vitro work relates to the physiological role of the protein.

Effects of lysozyme-thiocyanate combinations on the viability and lactic acid production of Streptococcus mutans and Streptococcus rattus

Effects of human lysozyme (HLZ) combined with thiocyanate (SCN-) ions on mutans streptococci, both in physiologic salivary concentrations, were studied. The bacteria were incubated for 75 min either in HLZ-supplemented sterilized human whole saliva (pH 5 and 7) or in neutral buffer in the presence or absence of HLZ (30 mg/l)-SCN- (1-5 mM) combinations. HLZ had no inhibitory effect on the viability of Streptococcus mutans, serotype c, either in saliva or in buffer, not even at pH 5, in the presence of salivary bicarbonate or in higher (up to 240 mg/l) concentrations of HLZ. In contrast, HLZ significantly decreased the viability of S. rattus in both media. HLZ also effectively blocked the lactic acid production of S. rattus but not that of S. mutans. Thiocyanate ions, which have been proposed to enhance the antimicrobial activity of lysozyme, did not affect the antibacterial activity of HLZ or HLZ-HCO3- combinations. It is concluded that the in vivo levels of SCN- ions, which constitute an integral part of the peroxidase antimicrobial system in saliva, may not be high enough to trigger the lysis of S. mutans by lysozyme in human saliva. The very low prevalence of S. rattus compared with S. mutans in human populations may be associated with their different susceptibility to lysozyme-mediated inhibition in saliva.

Lysozyme-protease-inorganic monovalent anion lysis of oral bacterial strains in buffers and stimulated whole saliva

Similar to Streptococcus mutans, buffer suspensions of Lactobacillus casei, Lactobacillus plantarum, and Fusobacterium nucleatum all undergo cell lysis when treated with the lysozyme-protease-inorganic monovalent anion antibacterial system. For Lactobacillus species treated with lysozyme and proteases at pHs of 4 and 5.3, lysis resulted when a lytic activating concentration of bicarbonate anion followed enzyme treatment. Furthermore, synergistic lysis of these bacteria was noted when lysozyme-protease treatment was followed by bicarbonate anion used in combination with chloride or fluoride anions. Noteworthy, the halides were not active in promoting lysis when used by themselves in the absence of bicarbonate. For F. nucleatum suspended at pH 6.9, lysis was dependent upon the ionic strength of the buffer and resulted when lysozyme-protease treatment of the organism was followed by 100 mmol/L bicarbonate activation. When lysozyme and proteases were omitted from the incubation mixtures and replaced by stimulated whole saliva, pH 5.3, lysis was observed only with L. plantarum and S. mutans, but not with L. casei. The latter could be lysed, however, if suspended in saliva which was diluted several-fold with distilled water. In experiments where lysozyme was selectively depleted from whole saliva by immunoadsorption affinity chromatography, the great majority of the lysis capability of the saliva for L. plantarum was lost, although a significant degree of lysis appeared to be due to salivary factors other than lysozyme. F. nucleatum was also found to lyse in saliva at neutral pH, suggesting that both Gram-positive and Gram-negative oral bacteria may be susceptible to this antibacterial system in vivo.