Inhibition of Streptococcus mutans by the lactoperoxidase antimicrobial system

Modified Lactoperoxidase System as a Promising Anticaries Agent: In Vitro Studies on Streptococcus mutans Biofilms

The lactoperoxidase (LPO) system shows promise in the prevention of dental caries, a common chronic disease. This system has antimicrobial properties and is part of the non-specific antimicrobial immune system. Understanding the efficacy of the LPO system in the fight against biofilms could provide information on alternative strategies for the prevention and treatment of caries. In this study, the enzymatic system was modified using four different (pseudo)halide substrates (thiocyanate, thiocyanate-iodide mixture, selenocyanate, and iodide). The study evaluated the metabolic effects of applying such modifications to Streptococcus mutans; in particular: (1) biofilm formation, (2) synthesis of insoluble polysaccharides, (3) lactate synthesis, (4) glucose and sucrose consumption, (5) intracellular NAD+ and NADH concentrations, and (6) transmembrane glucose transport efficiency (PTS activity). The results showed that the LPO-iodide system had the strongest inhibitory effect on biofilm growth and lactate synthesis (complete inhibition). This was associated with an increase in the NAD+/NADH ratio and an inhibition of glucose PTS activity. The LPO-selenocyanate system showed a moderate inhibitory effect on biofilm biomass growth and lactate synthesis. The other systems showed relatively small inhibition of lactate synthesis and glucose PTS but no effect on the growth of biofilm biomass. This study provides a basis for further research on the use of alternative substrates with the LPO system, particularly the LPO-iodide system, in the prevention and control of biofilm-related diseases.

Resistance of Streptococcus pneumoniae to hypothiocyanous acid generated by host peroxidases

Streptococcus pneumoniae is a serious human respiratory pathogen. It generates hydrogen peroxide (H₂O₂) as part of its normal metabolism, yet it lacks enzymes that remove this oxidant. Here we show that lactoperoxidase and myeloperoxidase, two host enzymes present in the respiratory tract, convert bacterial H₂O₂ into HOSCN that S. pneumoniae can resist. We found that incubation of S. pneumoniae with myeloperoxidase in chloride-rich buffer killed the bacteria due to formation of toxic hypochlorous acid (HOCl). However, the addition of physiological concentrations of thiocyanate protected the bacteria. Similarly, S. pneumoniae remained viable in the presence of lactoperoxidase and thiocyanate even though the majority of bacterial H₂O₂ was converted to hypothiocyanous acid (HOSCN). S. pneumoniae and Pseudomonas aeruginosa, another respiratory pathogen, were similarly sensitive to H₂O₂ and HOCl. In contrast, S. pneumoniae tolerated much higher doses of HOSCN than P. aeruginosa. When associated with neutrophil extracellular traps (NETs), S. pneumoniae continued to generate H₂O₂, which was converted to HOCl by MPO present on NETs. However, there was no loss in bacterial viability because HOCl was scavenged by the NET proteins. We conclude that at sites of infection, bacteria will be protected from HOCl by thiocyanate and extracellular proteins including those associated with NETs. Resistance to HOSCN may give S. pneumoniae a survival advantage over other pathogenic bacteria. Understanding the mechanisms by which S. pneumoniae protects itself from HOSCN may reveal novel strategies for limiting the colonization and pathogenicity of this deadly pathogen.

Glutathione utilization protects Streptococcus pneumoniae against lactoperoxidase-derived hypothiocyanous acid

Streptococcus pneumoniae is the leading cause of community-acquired pneumonia, resulting in more than one million deaths each year worldwide. This pathogen generates large amounts of hydrogen peroxide (H₂O₂), which will be converted to hypothiocyanous acid (HOSCN) by lactoperoxidase (LPO) in the human respiratory tract. S. pneumoniae has been shown to be more resistant to HOSCN than some bacteria, and sensitizing S. pneumoniae to HOSCN may be a novel treatment strategy for combating this deadly pathogen. In this study we investigated the role of the low molecular weight thiol glutathione in HOSCN resistance. S. pneumoniae does not synthesize glutathione but imports it from the environment via an ABC transporter. Upon treatment of S. pneumoniae with HOSCN, bacterial glutathione was reversibly oxidized in a time- and dose-dependent manner, and intracellular proteins became glutathionylated. Bacterial death was observed when the reduced glutathione pool dropped below 20%. A S. pneumoniae mutant unable to import glutathione (ΔgshT) was more readily killed by exogenous HOSCN. Furthermore, bacterial growth in the presence of LPO converting bacterial H₂O₂ to HOSCN was significantly impeded in mutants that were unable to import glutathione, or mutants unable to recycle oxidized glutathione (Δgor). This research highlights the importance of glutathione in protecting S. pneumoniae from HOSCN. Limiting glutathione utilization by S. pneumoniae may be a way to limit colonization and pathogenicity.

Reverse Ordered Sequential Mechanism for Lactoperoxidase with Inhibition by Hydrogen Peroxide

Lactoperoxidase (LPO, Fe^III in its resting state in the absence of substrates)—an enzyme secreted from human mammary, salivary, and other mucosal glands—catalyzes the oxidation of thiocyanate (SCN⁻) by hydrogen peroxide (H₂O₂) to produce hypothiocyanite (OSCN⁻), which functions as an antimicrobial agent. The accepted catalytic mechanism, called the halogen cycle, comprises a two-electron oxidation of LPO by H₂O₂ to produce oxoiron(IV) radicals, followed by O-atom transfer to SCN⁻. However, the mechanism does not explain biphasic kinetics and inhibition by H₂O₂ at low concentration of reducing substrate, conditions that may be biologically relevant. We propose an ordered sequential mechanism in which the order of substrate binding is reversed, first SCN⁻ and then H₂O₂. The sequence of substrate binding that is described by the halogen cycle mechanism is actually inhibitory.

The Significance of Lactoperoxidase System in Oral Health: Application and Efficacy in Oral Hygiene Products

Lactoperoxidase (LPO) present in saliva are an important element of the nonspecific immune response involved in maintaining oral health. The main role of this enzyme is to oxidize salivary thiocyanate ions (SCN^-) in the presence of hydrogen peroxide (H₂O₂) to products that exhibit antimicrobial activity. LPO derived from bovine milk has found an application in food, cosmetics, and medical industries due to its structural and functional similarity to the human enzyme. Oral hygiene products enriched with the LPO system constitute an alternative to the classic fluoride caries prophylaxis. This review describes the physiological role of human salivary lactoperoxidase and compares the results of clinical trials and in vitro studies of LPO alone and complex dentifrices enriched with bovine LPO. The role of reactivators and inhibitors of LPO is discussed together with the possibility of using nanoparticles to increase the stabilization and activity of this enzyme.

Extending Shelf Life of Indonesian Soft Milk Cheese (Dangke) by Lactoperoxidase System and Lysozyme

Dangke, a type of fresh soft cheese made of bovine and buffalo milk, is a traditional dairy product used in South Sulawesi, Indonesia. It is prepared from fresh milk using the conventional method, which easily destroys the quality. This study was conducted to assess whether using lactoperoxidase system and lysozyme as preservative agents could suppress the growth of bacteria in dangke. The pH value, total microbial count, and hardness of dangke were determined to measure the quality. Lactoperoxidase and lysozyme were purified from fresh bovine milk, and their purity was confirmed using SDS-PAGE. The combination of lactoperoxidase system and lysozyme was able to remarkably suppress the total microbial count in dangke from 7.78 ± 0.67 to 5.30 ± 0.42 log CFU/ml during 8 h of storage at room temperature. Preserving dangke in this enzyme combination affected its hardness, but there was no remarkable change in the pH value. Results of this study may provide knowledge to utilize a new method to preserve the quality of dangke.

Antimicrobial Capacity of Casein Phosphopeptide/Amorphous Calcium Phosphate and Enzymes in Glass Ionomer Cement in Dentin Carious Lesions

OBJECTIVE

To evaluate the ability of casein phosphopeptide/amorphous calcium phosphate (CPP/ACP) and lysozyme, lactoferrin, and lactoperoxidase (LLL) added to glass ionomer cement (GIC) to inhibit the growth of S. mutans in a caries model.

MATERIAL AND METHODS

Eighty permanent third molars were selected. The dentin of these teeth was exposed and flattened. Except for the coronal dentin, the specimens were waterproofed, autoclaved, and submitted to cariogenic challenge with standard strain of S. mutans. The carious lesions were sealed as follows: group 1 (n=20): GIC without additives; group 2 (n=20): GIC + CPP/ACP; group 3 (n=20): GIC + LLL; group 4 (n=20): GIC + CPP/ACP + LLL. S. mutans counts were performed before the caries were sealed (n=5), after 24 hours (n=5), at 1 month (n=5), and at 6 months (n=5). The results were analyzed using descriptive statistical analysis and the Kruskal-Wallis test (Student-Newman-Keuls test).

RESULTS

GIC + LLL caused a significant reduction of S. mutans 1 month after sealing (p<0.01); however, there was a significant growth of S. mutans 6 months after sealing. GIC, GIC + CPP/ACP, and GIC + CPP/ACP + LLL showed similar behavior with significant reduction of S. mutans after 24 hours (p<0.05) and increase after 1 and 6 months.

CONCLUSION

The addition of LLL to GIC increases the antimicrobial action of GIC on S. mutans. This leads to control of bacterial biofilm for 1 month, thus stopping the progression of carious lesions.

Inactivating effects of the lactoperoxidase system on bacterial lyases involved in oral malodour production

The main components of oral malodour have been identified as volatile sulfur compounds (VSCs), including hydrogen sulfide (H(2)S) and methyl mercaptan (CH(3)SH). The lactoperoxidase (LPO) system (consisting of LPO, glucose oxidase, glucose and thiocyanate) was previously shown to exhibit antimicrobial activities against some oral bacteria in vitro and suppressive effects on VSCs in mouth air in a clinical trial. Here, we examined the in vitro effects of the LPO system on the activities of the bacterial lyases involved in the production of VSCs by oral anaerobes. The exposure of crude bacterial extracts of Fusobacterium nucleatum and Porphyromonas gingivalis or purified methionine γ-lyase to the LPO system resulted in the inactivation of their lyase activities through l-cysteine and l-methionine, which was linked to the production of H(2)S and CH(3)SH, respectively. The exposure of living F. nucleatum and P. gingivalis cells to the LPO system resulted in the suppression of cell numbers and lyase activities. The inactivation of the crude bacterial extracts of F. nucleatum and purified methionine γ-lyase by the LPO system was partly recovered by the addition of DTT. Therefore, the LPO system may inactivate bacterial lyases including methionine γ-lyase by reacting with the free cysteine residues of lyases. These results suggested that the LPO system suppresses the production of VSCs not only through its antimicrobial effects, but also by its inactivating effects on the bacterial lyases of F. nucleatum and P. gingivalis.

Mode of action of lactoperoxidase as related to its antimicrobial activity: a review

Lactoperoxidase is a member of the family of the mammalian heme peroxidases which have a broad spectrum of activity. Their best known effect is their antimicrobial activity that arouses much interest in in vivo and in vitro applications. In this context, the proper use of lactoperoxidase needs a good understanding of its mode of action, of the factors that favor or limit its activity, and of the features and properties of the active molecules. The first part of this review describes briefly the classification of mammalian peroxidases and their role in the human immune system and in host cell damage. The second part summarizes present knowledge on the mode of action of lactoperoxidase, with special focus on the characteristics to be taken into account for in vitro or in vivo antimicrobial use. The last part looks upon the characteristics of the active molecule produced by lactoperoxidase in the presence of thiocyanate and/or iodide with implication(s) on its antimicrobial activity.

Comparative reactivity of myeloperoxidase-derived oxidants with mammalian cells

Myeloperoxidase is an important heme enzyme released by activated leukocytes that catalyzes the reaction of hydrogen peroxide with halide and pseudo-halide ions to form various hypohalous acids. Hypohalous acids are chemical oxidants that have potent antibacterial, antiviral, and antifungal properties and, as such, play key roles in the human immune system. However, increasing evidence supports an alternative role for myeloperoxidase-derived oxidants in the development of disease. Excessive production of hypohalous acids, particularly during chronic inflammation, leads to the initiation and accumulation of cellular damage that has been implicated in many human pathologies including atherosclerosis, neurodegenerative disease, lung disease, arthritis, inflammatory cancers, and kidney disease. This has sparked a significant interest in developing a greater understanding of the mechanisms involved in myeloperoxidase-derived oxidant-induced mammalian cell damage. This article reviews recent developments in our understanding of the cellular reactivity of hypochlorous acid, hypobromous acid, and hypothiocyanous acid, the major oxidants produced by myeloperoxidase under physiological conditions.

Molecular and structural basis of glutathione import in Gram-positive bacteria via GshT and the cystine ABC importer TcyBC of Streptococcus mutans

Glutathione (GSH) protects cells against oxidative injury and maintains a range of vital functions across all branches of life. Despite recent advances in our understanding of the transport mechanisms responsible for maintaining the spatiotemporal homeostasis of GSH and its conjugates in eukaryotes and Gram-negative bacteria, the molecular and structural basis of GSH import into Gram-positive bacteria has remained largely uncharacterized. Here, we employ genetic, biochemical and structural studies to investigate a possible glutathione import axis in Streptococcus mutans, an organism that has hitherto served as a model system. We show that GshT, a type 3 solute binding protein, displays physiologically relevant affinity for GSH and glutathione disulfide (GSSG). The crystal structure of GshT in complex with GSSG reveals a collapsed structure whereby the GS-I-leg of GSSG is accommodated tightly via extensive interactions contributed by the N- and C-terminal lobes of GshT, while the GS-II leg extends to the solvent. This can explain the ligand promiscuity of GshT in terms of binding glutathione analogues with substitutions at the cysteine-sulfur or the glycine-carboxylate. Finally, we show that GshT primes glutathione import via the L-cystine ABC transporter TcyBC, a membrane permease, which had previously exclusively been associated with the transport of L-cystine.

Hypothiocyanous acid: benign or deadly?

Hypothiocyanous acid (HOSCN) is produced in biological systems by the peroxidase-catalyzed reaction of thiocyanate (SCN(-)) with H(2)O(2). This oxidant plays an important role in the human immune system, owing to its potent bacteriostatic properties. Significant amounts of HOSCN are also formed by immune cells under inflammatory conditions, yet the reactivity of this oxidant with host tissue is poorly characterized. Traditionally, HOSCN has been viewed as a mild oxidant, which is innocuous to mammalian cells. Indeed, recent studies show that the presence of SCN(-) in airways has a protective function, by preventing the formation of other, more damaging, inflammatory oxidants. However, there is an increasing body of evidence that challenges this dogma, showing that the selectivity of HOSCN for specific thiol-containing cellular targets results in the initiation of significant cellular damage. This propensity to induce cellular dysfunction is gaining considerable interest, particularly in the cardiovascular field, as smokers have elevated plasma SCN(-), the precursor for HOSCN. This review will outline the beneficial and detrimental aspects of HOSCN formation in biological systems.

Differential response of Streptococcus mutans towards friend and foe in mixed-species cultures

In the oral biofilm, the 'mitis' streptococci are among the first group of organisms to colonize the tooth surface. Their proliferation is thought to be an important factor required for antagonizing the growth of cariogenic species such as Streptococcus mutans. In this study, we used a three-species mixed culture to demonstrate that another ubiquitous early colonizing species, Veillonella parvula, can greatly affect the outcome of the competition between a pair of antagonists such as S. mutans and Streptococcus gordonii. Transcriptome analysis further revealed that S. mutans responds differentially to its friend (V. parvula) and foe (S. gordonii). In the mixed culture with S. gordonii, all but one of the S. mutans sugar uptake and metabolic genes were downregulated, while genes for alternative energy source utilization and H₂O₂ tolerance were upregulated, resulting in a slower but persistent growth. In contrast, when cultured with V. parvula, S. mutans grew equally well or better than in monoculture and exhibited relatively few changes within its transcriptome. When V. parvula was introduced into the mixed culture of S. mutans and S. gordonii, it rescued the growth inhibition of S. mutans. In this three-species environment, S. mutans increased the expression of genes required for the uptake and metabolism of minor sugars, while genes required for oxidative stress tolerance were downregulated. We conclude that the major factors that affect the competition between S. mutans and S. gordonii are carbohydrate utilization and H₂O₂ resistance. The presence of V. parvula in the tri-species culture mitigates these two major factors and allows S. mutans to proliferate, despite the presence of S. gordonii.

The role of hypothiocyanous acid (HOSCN) in biological systems

Hypohalous acids (HOX), produced by peroxidase-catalysed reactions of halide and pseudohalide ions with H(2)O(2), play an important role in the human immune system. However, there is compelling evidence that these oxidants also mediate host tissue damage and contribute to the progression of a number of inflammatory diseases. Although it is well established that significant amounts of hypothiocyanous acid (HOSCN) are formed under physiological conditions, the reactions of this oxidant with host biological systems are relatively poorly characterized. It is generally accepted that HOSCN is a mild oxidant that reacts selectively with thiols. However, it is becoming increasingly recognized that this selectivity can result in the induction of significant cellular damage, which may contribute to disease. This review will outline the formation and reactivity of HOSCN and the role of this oxidant in biological systems.

Effect of lactoperoxidase system containing toothpaste on cariogenic bacteria in children with early childhood caries

BACKGROUND AND OBJECTIVES

Lactoperoxidase system contains Lactoperoxidase, Hydrogen peroxide and Thiocyanate ions, which have inhibitory action against cariogenic oral microflora. The present study was undertaken to assess the effect of lactoperoxidase system containing toothpaste on cariogenic microflora in children with early childhood caries.

METHODS

Study group included 30 children with Early Childhood Caries. 15 were considered as test group who used the test product Biotene toothpaste and other 15 as control group who used Colgate Active as control product. Salivary samples were analyzed for mutans streptococci (MS) and Lactobacilli, and for the levels of Thiocyanate ions.

RESULTS

Showed significant increase in the levels of Thiocyanate ion in saliva during experimental period. Compared to the control group test group showed significant increase in the levels of thiocyanate ions during experimental and washout period, whereas the number of colonies of MS and Lactobacilli were significantly reduced in test group during experimental period.

CONCLUSION

The levels of thiocyanate ions can be increased in vivo by supplementing the saliva with natural enzymes like lactoperoxidase. This increased concentration of thiocyanate will reduce the number of cariogenic microflora in children with Early Childhood Caries.

Influence of a model human defensive peroxidase system on oral streptococcal antagonism

Streptococcus is a dominant genus in the human oral cavity, making up about 20 % of the more than 800 species of bacteria that have been identified, and about 80 % of the early biofilm colonizers. Oral streptococci include both health-compatible (e.g. Streptococcus gordonii and Streptococcus sanguinis) and pathogenic strains (e.g. the cariogenic Streptococcus mutans). Because the streptococci have similar metabolic requirements, they have developed defence strategies that lead to antagonism (also known as bacterial interference). S. mutans expresses bacteriocins that are cytotoxic toward S. gordonii and S. sanguinis, whereas S. gordonii and S. sanguinis differentially produce H(2)O(2) (under aerobic growth conditions), which is relatively toxic toward S. mutans. Superimposed on the inter-bacterial combat are the effects of the host defensive mechanisms. We report here on the multifarious effects of bovine lactoperoxidase (bLPO) on the antagonism between S. gordonii and S. sanguinis versus S. mutans. Some of the effects are apparently counterproductive with respect to maintaining a health-compatible population of streptococci. For example, the bLPO system (comprised of bLPO+SCN(-)+H(2)O(2)) destroys H(2)O(2), thereby abolishing the ability of S. gordonii and S. sanguinis to inhibit the growth of S. mutans. Furthermore, bLPO protein (with or without its substrate) inhibits bacterial growth in a biofilm assay, but sucrose negates the inhibitory effects of the bLPO protein, thereby facilitating adherence of S. mutans in lieu of S. gordonii and S. sanguinis. Our findings may be relevant to environmental pressures that select early supragingival colonizers.

Redox warfare between airway epithelial cells and Pseudomonas: dual oxidase versus pyocyanin

The importance of reactive oxygen species-dependent microbial killing by the phagocytic cell NADPH oxidase has been appreciated for some time, although only recently has an appreciation developed for the partnership of lactoperoxidase with related dual oxidases (Duox) within secretions of the airway surface layer. This system produces mild oxidants designed for extracellular killing that are effective against several airway pathogens, including Staphylococcus aureus, Burkholderia cepacia, and Pseudomonas aeruginosa. Establishment of chronic pseudomonas infections involves adaptations to resist oxidant-dependent killing by expression of a redox-active virulence factor, pyocyanin, that competitively inhibits epithelial Duox activity by consuming intracellular NADPH and producing superoxide, thereby inflicting oxidative stress on the host.

Inorganic chemistry of defensive peroxidases in the human oral cavity

The innate host response system is comprised of various mechanisms for orchestrating host response to microbial infection of the oral cavity. The heterogeneity of the oral cavity and the associated microenvironments that are produced give rise to different chemistries that affect the innate defense system. One focus of this review is on how these spatial differences influence the two major defensive peroxidases of the oral cavity, salivary peroxidase (SPO) and myeloperoxidase (MPO). With hydrogen peroxide (H(2)O(2)) as an oxidant, the defensive peroxidases use inorganic ions to produce antimicrobials that are generally more effective than H(2)O(2) itself. The concentrations of the inorganic substrates are different in saliva vs. gingival crevicular fluid (GCF). Thus, in the supragingival regime, SPO and MPO work in unison for the exclusive production of hypothiocyanite (OSCN(-), a reactive inorganic species), which constantly bathes nascent plaques. In contrast, MPO is introduced to the GCF during inflammatory response, and in that environment it is capable of producing hypochlorite (OCl(-)), a chemically more powerful oxidant that is implicated in host tissue damage. A second focus of this review is on inter-person variation that may contribute to different peroxidase function. Many of these differences are attributed to dietary or smoking practices that alter the concentrations of relevant inorganic species in the oral cavity (e.g.: fluoride, F(-); cyanide, CN(-); cyanate, OCN(-); thiocyanate, SCN(-); and nitrate, NO(3)(-)). Because of the complexity of the host and microflora biology and the associated chemistry, it is difficult to establish the significance of the human peroxidase systems during the pathogenesis of oral diseases. The problem is particularly complex with respect to the gingival sulcus and periodontal pockets (where the very different defensive stratagems of GCF and saliva co-mingle). Despite this complexity, intriguing in vitro and in vivo studies are reviewed here that reveal the interplay between peroxidase function and associated inorganic chemistry.

Mammalian heme peroxidases: from molecular mechanisms to health implications

A marked increase in interest has occurred over the last few years in the role that mammalian heme peroxidase enzymes, primarily myeloperoxidase, eosinophil peroxidase, and lactoperoxidase, may play in both disease prevention and human pathologies. This increased interest has been sparked by developments in our understanding of polymorphisms that control the levels of these enzymes, a greater understanding of the basic chemistry and biochemistry of the oxidants formed by these species, the development of specific biomarkers that can be used in vivo to detect damage induced by these oxidants, the detection of active forms of these peroxidases at most, if not all, sites of inflammation, and a correlation between the levels of these enzymes and a number of major human pathologies. This article reviews recent developments in our understanding of the enzymology, chemistry, biochemistry and biologic roles of mammalian peroxidases and the oxidants that they generate, the potential role of these oxidants in human disease, and the use of the levels of these enzymes in disease prognosis.

Origin, structure, and biological activities of peroxidases in human saliva

Human whole saliva contains two peroxidases, salivary peroxidase (hSPO) and myeloperoxidase (hMPO), which are part of the innate host defence in oral cavity. Both hSPO as well as human milk lactoperoxidase (hLPO) are coded by the same gene, but to what extent the different producing glands, salivary and mammary glands, affect the final conformation of the enzymes is not known. In human saliva the major function of hSPO and hMPO is to catalyze the oxidation of thiocyanate (SCN(-)) in the presence of hydrogen peroxide (H(2)O(2)) resulting in end products of wide antimicrobial potential. In addition cytotoxic H(2)O(2) is degraded. Similar peroxidation reactions inactivate some mutagenic and carcinogenic compounds, which suggests another protective mechanism of peroxidases in human saliva. Although being target of an active antimicrobial research, the structure-function relationships of hSPO are poorly known. However, recently published method for recombinant hSPO production offers new tools for those investigations.

Effect of the lactoperoxidase system against three major causal agents of disease in mangoes

The antibacterial activity of the lactoperoxidase system (LPS) on the growth of Xanthomonas campestris, the causal agent of bacterial black spot in mangoes, Botryodiplodia theobromae, the causal agent of stem-end rot disease in mangoes, and Colletotrichum gloeosporioides, the causal agent of anthracnose disease in mangoes, was determined during culture at 30 degrees C and at several pH values (4.5, 5.5, and 6.5). When the results of using the LPS were compared with those from control cultures without the LPS reagents, the growth of the three microorganisms was totally inhibited in all of the conditions tested. Viability tests enumerating cultivable cells of X. campestris showed that the LPS had a bactericidal effect, whatever the pH value. This effect is faster at pH 5.5, corroborating the results reported in the literature (optimal pH for the LPS efficiency). Further, we proved that hydrogen peroxide alone had little inhibition effect on the growth of the microorganisms studied. This compound is essentially used to convert thiocyanate into hypothiocyanate during the lactoperoxidase reaction. The potential of the LPS for the postharvest treatment of the fruits for controlling microbial diseases was thus demonstrated. Nevertheless, further studies are needed on fresh fruits before envisaging any application.

Unique stress response to the lactoperoxidase-thiocyanate enzyme system in Escherichia coli

Using a differential fluorescence induction approach, we screened a promoter trap library constructed in a vector with a promoterless gfp gene for Escherichia coli MG1655 promoters that are induced upon challenge with the antimicrobial lactoperoxidase-thiocyanate enzyme system. None of the thirteen identified lactoperoxidase-inducible open reading frames was inducible by H(2)O(2) or by the superoxide generator plumbagin. However, analysis of specific promoters of known stress genes showed some of these, including recA, dnaK and sodA, to be inducible by the lactoperoxidase-thiocyanate enzyme system. The results show that the lactoperoxidase-thiocyanate enzyme system elicits a distinct stress response different from but partly overlapping other oxidative stress responses. Several of the induced genes or pathways may be involved in bacterial defense against the toxic effects of the lactoperoxidase-thiocyanate enzyme system.

Sensitivity of Helicobacter pylori to an innate defence mechanism, the lactoperoxidase system, in buffer and in human whole saliva

Helicobacter pylori has frequently been isolated from human dental plaque, and oral spread via saliva is thought to be one of its principal modes of transmission. Among other innate defence systems human saliva contains peroxidase enzymes and lysozyme. The sensitivity of H. pylori to physiological concentrations of lactoperoxidase and its salivary substrate thiocyanate, and different amounts of hydrogen peroxide (H(2)O(2)) was investigated in buffer and in human whole saliva. The effect of lysozyme was also studied in saliva. All tested H. pylori strains, ATCC 43504(T) and five clinical isolates, were efficiently inhibited by the peroxidase system with high concentrations of H(2)O(2) in buffer. The inhibition was stronger at lower pH. However, in human saliva these high concentrations of H(2)O(2) generated less hypothiocyanite, the antibacterial product of the peroxidase system and the effects of the peroxidase system were weaker. Physiological concentration of lysozyme was not bacteriocidal against H. pylori, nor did it enhance the effect of the peroxidase system in saliva. Thus, further studies are needed to enhance the efficacy of peroxidase systems in human saliva to make it more beneficial not only against dental but also against gastric pathogens.

The lactoperoxidase system increases efficacy of high-pressure inactivation of foodborne bacteria

The inactivation of eight different bacteria comprising Escherichia coli LMM1010 and MG1655, respectively a pressure-resistant strain and the corresponding wild-type, Salmonella Typhimurium, Pseudomonas fluorescens, Staphylococcus aureus, Enterococcus faecalis, Listeria innocua and Lactobacillus plantarum, by high hydrostatic pressure in skim milk supplemented with the lactoperoxidase-hydrogen peroxide-thiocyanate (LP) system at naturally occurring concentration was studied. In the absence of pressure treatment, the LP system had either no effect, i.e. on S. Typhimurium and E. coli LMM1010, a growth inhibiting effect, i.e. on E. coli MG1655, L. innocua, S. aureus, L. plantarum and E. faecalis, or a bactericidal effect, i.e. on P. fluorescens. The presence of the LP system affected inactivation by high pressure in a cell density-dependent manner. At low cell concentration (10(6) cfu/ml), the LP system strongly increased high-pressure inactivation as measured immediately after pressure treatment of all bacteria except the pressure-resistant E. coli. At high cell density (10(9) cfu/ml), only inactivation of L. innocua, E. faecalis and L. plantarum were enhanced. For both E. coli strains, the fate of the bacteria during 24 h following pressure treatment was also studied. It was found that in the presence of the LP system, considerable further inactivation occurred in the first hours after pressure treatment. The potential of the LP system to improve the bactericidal efficiency of high-pressure treatment for food preservation is discussed.

Symposium on 'nutritional effects of new processing technologies'. New processing technologies: an overview

Most food-preservation techniques act by slowing down or completely inhibiting the growth of micro-organisms. Few techniques act by inactivating them. While heat remains the technique most extensively used for inactivation, there has been increasing interest recently in the development of alternative approaches in response to the desires of consumers for products which are less organoleptically and nutritionally damaged during processing and less reliant on additives than previously. The new approaches, therefore, mostly involve technologies that offer full or partial alternatives to heat for the inactivation of bacteria, yeasts and moulds. They include the application to foods of high hydrostatic pressure, high-voltage electric discharges, high-intensity laser and non-coherent light pulses, 'manothermosonication' (the combination of mild heating with ultrasonication and slightly-raised pressure), and high-magnetic-field pulses. In addition, a number of naturally-occurring antimicrobials, including lysozyme and low-molecular-weight products of micro-organisms are finding increasing use. High pressure is being used commercially to non-thermally pasteurize a number of foods, while the other physical procedures are in various stages of development and commercial evaluation. Possible nutritional consequences have so far been given little attention compared with microbiological ones.

Glucosyltransferase inactivation reduces dental caries

Dental caries has been an intractable disease in spite of intense dental research. The metabolic acids produced by mutans streptococci demineralize the tooth surface and lead to dental caries. The enzyme glucosyltransferase (GTF) produced by mutans streptococci is the key factor in this process. Oral bacterial GTFs use sucrose as a substrate in synthesis of either water-soluble or insoluble glucans. In this investigation, kinetic studies with divalent metal ions revealed their strong binding affinity to GTF. The metal ions also proved to be strong inhibitors of the enzyme. Here we describe a simple method of inactivating the enzyme that actively participates in dental caries by taking advantage of a Fenton reaction which requires metal ions such as iron or copper and peroxide. The hydroxyl radical ions produced via the Fenton reaction inactivate GTF, a factor in the production of dental caries.

The effects of different (pseudo)halide substrates on peroxidase-mediated killing of Actinobacillus actinomycetemcomitans

Actinobacillus actinomycetemcomitans is a Gram-negative bacterium which has an important role in localized juvenile and in progressive periodontitis. It is sensitive to killing by the myeloperoxidase (MP)-hydrogen peroxide (H2O2)-chloride system which is part of the innate host defense mediated by polymorphonuclear leukocytes. Since it has been recently suggested that thiocyanate, instead of chloride, could serve as a main substrate for MP as for lactoperoxidase (LP) and salivary peroxidase, we investigated in this study the effect of both LP and MP systems on A. actinomycetemcomitans with different (pseudo)halide substrates, thiocyanate, chloride and iodide. The concentrations of the substrates were physiological for oral fluids, as was the concentration range of H2O2. Both peroxidases produced end products with identical antibacterial activity with thiocyanate and iodide. The oxidation of iodide resulted in the highest antimicrobial efficiency followed by chloride and thiocyanate. Addition of thiocyanate into either MP-H2O2-chloride or MP/LP-H2O2-iodide system abolished the bactericidal activity of the oxidized halide. However, the chloride did not affect the bactericidality of the MP-H2O2-iodide system, but when all 3 (pseudo)halide substrates were present no antimicrobial effect was recorded. Our study shows that the presence of thiocyanate in physiological amounts is able to prevent the bactericidal activity of halide-peroxidase systems in low H2O2 concentrations. These results explain why thiocyanate-peroxidase systems of either innate origin (saliva, crevicular fluid) or introduced by commercial oral hygiene products are most probably ineffective against A. actinomycetemcomitans in vivo. Further studies of halide/thiocyanate ratio are needed to develop products which are also effective against oral anaerobes.

Cytochemical detection of endogenous peroxidase in the acinar cells of the hamster submandibular gland

The presence of endogenous peroxidase activity in the hamster submandibular gland was investigated cytochemically by light and electron microscopy using diaminobenzidine methods. After fixation of tissue with 2% paraformaldehyde-2.5% glutaraldehyde and incubation in a DAB reaction medium containing 0.01% H2O2, the peroxidase reaction product was localized in the nuclear envelope, the cisternae of the endoplasmic reticulum, secretory granules and the Golgi apparatus in both the acinar and granular duct cells of the submandibular gland. This is in contrast to earlier investigators who failed to detect peroxidase activity in acinar cells of the hamster submandibular gland and reported that peroxidase is localized only in the granular duct cells. The discrepancy may be caused by differences in experimental procedures. It is suggested that fixation of tissue with a high concentration of glutaraldehyde and incubation in a DAB reaction medium containing a high concentration of H2O2 inhibits the peroxidase activity of acinar cells in the hamster submandibular gland.

Enzymatic removal and disinfection of bacterial biofilms

Model biofilms of Staphylococcus aureus, Staphylococcus epidermidis, Pseudomonas fluorescens, and Pseudomonas aeruginosa were made on steel and polypropylene substrata. Plaque-resembling biofilms of Streptococcus mutans, Actinomyces viscosus, and Fusobacterium nucleatum were made on saliva-coated hydroxyapatite. The activity of enzymes against bacterial cells in biofilm was measured by fluorescence microscopy and an indirect conductance test in which evolution of carbon dioxide was measured. Glucose oxidase combined with lactoperoxidase was bactericidal against biofilm bacteria but did not remove the biofilm from the substrata. A complex mixture of polysaccharide-hydrolyzing enzymes was able to remove bacterial biofilm from steel and polypropylene substrata but did not have a significant bactericidal activity. Combining oxidoreductases with polysaccharide-hydrolyzing enzymes resulted in bactericidal activity as well as removal of the biofilm.

An evaluation of a dentifrice containing salivary peroxidase elements for the control of gingival disease in patients with irradiated head and neck cancer

Patients who have undergone irradiation for head and neck tumors commonly have xerostomia. Loss of the protective constituents normally found in saliva leaves patients at greater risk for development of significant dental pathologic disorders, including gingival and periodontal disease. Periodontal disease and tooth extractions are currently accepted as etiologic factors for the development of osteoradionecrosis. This double-blind crossover trial was conducted to assess the efficacy of a dentifrice containing salivary peroxidase elements in the reduction of gingivitis in a population of patients with irradiated cancer. Subjects were instructed to brush with the dentifrice provided. Plaque and gingival index values were obtained and statistically compared with baseline values. A weak positive effect was found between use of the dentifrice and a reduction in gingival inflammation. Patient compliance was a limiting factor in this treatment effect. The results suggest possible efficacy for the dentifrice in augmenting traditional measures of postradiation oral health maintenance.

Does variability in salivary protein concentrations influence oral microbial ecology and oral health?

Salivary protein interactions with oral microbes in vitro include aggregation, adherence, cell-killing, inhibition of metabolism, and nutrition. Such interactions might be expected to influence oral ecology. However, inconsistent results have been obtained from in vivo tests of the hypothesis that quantitative variation in salivary protein concentrations will affect oral disease prevalence. Results may have been influenced by choices made during study design, including saliva source, stimulation status, control for flow rate, and assay methods. Salivary protein concentrations also may be subject to circadian variation. Values for saliva collected at the same time of day tend to remain consistent within subjects, but events such as stress, inflammation, infection, menstruation, or pregnancy may induce short-term changes. Long-term factors such as aging, systemic disease, or medication likewise may influence salivary protein concentrations. Such sources of variation may increase the sample size needed to find statistically significant differences. Clinical studies also must consider factors such as human population variation, strain and species differences in protein-microbe interactions, protein polymorphism, and synergistic or antagonistic interaction between proteins. Salivary proteins may form heterotypic complexes with unique effects, and different proteins may exert redundant effects. Patterns of protein-microbe interaction also may differ between oral sites. Future clinical studies must take those factors into account. Promising approaches might involve meta-analysis or multi-center studies, retrospective and prospective longitudinal designs, short-term measurement of salivary protein effects, and consideration of individual variation in multiple protein effects such as aggregation, adherence, and cell-killing.

Calcitonin gene-related peptide (CGRP) and its effects on protein release in vitro in the developing submandibular gland of the rat

Indirect immunohistochemical methods were used to study presence and number of CGRP-immunoreactive (CGRP-IR) nerve fibers in the submandibular gland and ganglion cells of the superior cervical, submandibular and trigeminal ganglia of the developing rat. The effect of CGRP on peroxidase and total protein release was also studied in the developing postnatal submandibular glands of 1, 5, 12 and 30-day-old, as well as adult rats by in vitro methods. The possible costimulation of CGRP with SP, NKA or carbachol on 5-day-old and adult rats was also tested. The stimulatory effects of these compounds were compared to the basic release of peroxidase and total amount of proteins from submandibular gland fragments in incubation solution. CGRP-IR nerve fibers were found in relatively high number during post-natal development, mainly around blood vessels and ducts. Some CGRP-IR nerve fibers were also detected around acini. The number of these fibers was quite low and remained constant during the post-natal development. The number of CGRP-IR trigeminal ganglion cells was higher on the 5th and 12th post-natal day than later in development and in adult animals. At the same time, superior cervical- and submandibular ganglion cells were non-reactive for CGRP, suggesting trigeminal origin of CGRP-IR nerve fibers during the development in the submandibular gland. In the secretory studies, CGRP per se stimulated both peroxidase and total protein release in the submandibular gland most effectively on 5th and 12th post-natal days, while there was no clear secretory response in the adult glands. In the 5-day-old submandibular gland CGRP in combination with SP, NKA or carbachol clearly enhanced the total protein secretory response when compared with the release caused by these substances alone. However, in the adult submandibular gland, the combinations did not enhance total protein release more than any of the substances alone. Furthermore, it can be concluded that the presence of a more dense CGRP-IR innervation during the early postnatal period in the developing submandibular gland is accompanied with an increased responsiveness of the secretory elements to CGRP.

Effects of a lactoperoxidase-system-containing toothpaste on dental plaque and whole saliva in vivo

The effects of a lactoperoxidase-system-containing toothpaste. Biotene, on saliva and dental plaque were studied. In a double-blind crossover study 20 healthy volunteers used an experimental (comprising the complete peroxidase system) or a placebo (without lactoperoxidase, KSCN, and glucose oxidase) toothpaste twice daily for 2 weeks separated by a 2-week washout period. At base lines and at the end of both test periods saliva and plaque samples were collected, and plaque pH changes were monitored. Saliva was analyzed for hypothiocyanite (HOSCN/OSCN-) and thiocyanate (SCN-) concentrations and salivary peroxidase activity. The amount of total streptococci, mutans streptococci, lactobacilli, and total anaerobic flora was determined both in saliva and in plaque samples. The accumulation and the acidogenicity of plaque were also quantitated. A 2-week daily use of Biotene had no effect on salivary flow rate, peroxidase activity, HOSCN/OSCN-, SCN-, or any of the monitored bacterial counts compared with the placebo toothpaste. The accumulation of dental plaque was not affected by the lactoperoxidase-system-containing toothpaste. The acidogenicity of plaque did not change significantly, nor did the two test dentifrices differ in their ability to inhibit the plaque pH drop caused by sucrose in subjects with normal salivary flow rate.

Antibacterial activity of hydrogen peroxide and the lactoperoxidase-hydrogen peroxide-thiocyanate system against oral streptococci

In secreted fluids, the enzyme lactoperoxidase (LP) catalyzes the oxidation of thiocyanate ion (SCN-) by hydrogen peroxide (H2O2), producing the weak oxidizing agent hypothiocyanite (OSCN-), which has bacteriostatic activity. However, H2O2 has antibacterial activity in the absence of LP and thiocyanate (SCN-). Therefore, LP may increase antibacterial activity by using H2O2 to produce a more effective inhibitor of bacterial metabolism and growth, or LP may protect bacteria against the toxicity of H2O2 by converting H2O2 to a less-potent oxidizing agent. To clarify the role of LP, the antibacterial activities of H2O2 and the LP-H2O2-SCN- system were compared by measuring loss of viability and inhibition of bacterial metabolism and growth. The relative toxicity of H2O2 and the LP system to oral streptococci was found to depend on the length of time that the bacteria were exposed to the agents. During incubations of up to 4 h, the LP system was from 10 to 500 times more effective than H2O2 as an inhibitor of glucose metabolism, lactic acid production, and growth. However, if no more H2O2 was added, the concentration of the inhibitor OSCN- fell because of slow decomposition of OSCN-, and when OSCN- fell below 0.01 mM, the bacteria resumed metabolism and growth. In contrast, the activity of H2O2 increased with time. H2O2 persisted in the medium for long periods of time because H2O2 reacted slowly with the bacteria and streptococci lack the enzyme catalase, which converts H2O2 to oxygen and water. After 24 h of exposure, H2O2 was as effective as the LP system as an inhibitor of metabolism. H2O2 also caused a time-dependent loss of viability, whereas the LP system had little bactericidal activity. The concentration of H2O2 required to kill half the bacteria within 15 s was 1.8 M (6%) but fell to 0.3 M (1%) at 2 min, to 10 mM (0.03%) at 1 h, and to 0.2 mM (0.0007%) with a 24-h exposure. The results indicate that if high levels of H2O2 can be sustained for long periods of time, H2O2 is an effective bactericidal agent, and the presence of LP and SCN- protects streptococci against killing by H2O2. Nevertheless, the combination of LP, H2O2, and SCN- is much more effective than H2O2 alone as an inhibitor of bacterial metabolism and growth.

Chronology of peroxidase activity in the developing rat parotid gland

The course of development of salivary peroxidase, an enzyme that has an important role in oral defense mechanisms, has been well documented in rat submandibular glands. However, the only report on salivary peroxidase activity in the other major salivary glands of the rat has been a cytochemical study of the adult parotid gland. In the present investigation, the accumulation of salivary peroxidase activity in developing parotid glands of rats was followed both biochemically and cytochemically. Specific activity (units per mg protein) attributable to salivary peroxidase began at 1 day after birth, then rose rapidly but unevenly, with peaks at 21 and 70 days, and no difference between the sexes at any age. Activity per gland increased progressively to 42 days in both sexes and was significantly higher in males at 70 days. The cytochemical observations on peroxidase activity localized to the rough endoplasmic reticulum and secretory granules of the developing acini were well correlated with the biochemical findings. Peroxidase-negative cells occurred in immature acini at 1 and 7 days, but only in the intercalated ducts thereafter. This observation suggests that the acini are a source of some of the ductal cells, at least during early postnatal development. The developmental pattern of specific activity differed from those of other rat parotid secretory enzymes, indicating that control of their synthesis during development is noncoordinate. The patterns of specific activity of the parotid and submandibular glands were complementary, suggesting that their combined secretions may supply biologically significant peroxidase activity to the oral cavities of rats throughout postnatal development.

Inhibition of Candida albicans by the Peroxidase/SCN-/H2O2 system

Effects of the salivary peroxidase (SPO) system on the growth, glucose uptake and metabolic activities of oral bacteria are well documented but the effects on oral fungi are virtually unknown. Therefore, the viability of Candida albicans (ATCC 28366) exposed to the peroxidase/SCN-/H2O2 system was studied in sterilized saliva, in phosphate-buffered saline (PBS) and in potassium chloride. The growth of C. albicans in glucose-supplemented saliva was faster at pH 5.5 than at pH 7. The addition of the complete SPO (or lactoperoxidase) system to either sterilized saliva, KCl (50 microM) or PBS at pH 5.5 inhibited dose-dependently the viability of C. albicans in KCl, but no inhibition was found in PBS or saliva. Maximal inhibition was achieved in 2 h and with > 320 microM of peroxidase-generated HOSCN/OSCN-. However, physiological salivary concentrations of phosphate (> or = 1.0 mM) and PBS blocked the antifungal effect of HOSCN/OSCN-. The relative proportions of SCN- and H2O2 were critical to the antifungal effects. With 0.2 mM KSCN, a complete loss of viability was achieved, though the HOSCN/OSCN- concentrations did not exceed 100 microM. It is concluded that C. albicans is sensitive to HOSCN/OSCN- but salivary concentrations of phosphate block the antifungal effect of the peroxidase systems.

Lysozyme enhances the inhibitory effects of the peroxidase system on glucose metabolism of Streptococcus mutans

The combined effect of the salivary peroxidase system and lysozyme on the glucose uptake of Streptococcus mutans NCTC 10449 was investigated. The bacteria were grown to late-exponential phase, washed, re-suspended in buffer at pH6, and incubated with (1) 50 micrograms/mL lysozyme from human milk for 60 min; (2) 7-15 mumol/L hypothiocyanous acid/hypothiocyanite for 10 min; and (3) lysozyme for 60 min prior to addition of and incubation with hypothiocyanous acid/hypothiocyanite for 10 min. Glucose uptake was initiated by adding the bacterial suspensions to 10 mL of pre-warmed 50 mumol/L glucose containing 0.98 mumol/L D-(U-14C-)-glucose, and the mixture was incubated in a shaking water-bath at 37 degrees C. Samples were withdrawn at various time intervals, rapidly filtered through 0.45-microns membranes, washed with ice-chilled buffer, and the incorporated radioactivity determined. Lysozyme stimulated S. mutans glucose uptake slightly, but significantly inhibited S. rattus glucose metabolism. A 20-30% inhibition of radiolabeled glucose incorporation was observed with hypothiocyanous acid/hypothiocyanite alone. Incubation of the bacteria with lysozyme prior to addition of hypothiocyanous acid/hypothiocyanite containing peroxidase resulted in a total inhibition of the glucose uptake. In contrast, lysozyme in combination with hypothiocyanous acid/hypothiocyanite without peroxidase gave only a 30-50% inhibition. The addition of 5 mmol/L dithiothreitol after incubation with lysozyme and hypothiocyanous acid/hypothiocyanite eliminated the inhibition of the bacterial glucose uptake. The viability of S. mutans was not affected by treatment with any of the components used. Our results indicate that physiological concentrations of lysozyme and the salivary peroxidase system components have a synergistic effect which results in a significant inhibition of glucose metabolism by S. mutans.

Studies on the lactoperoxidase system: reaction kinetics and antibacterial activity using two methods for hydrogen peroxide generation

Components of the lactoperoxidase system were measured during incubation in Isosensitest broth, with enzymatic (glucose oxidase, GO) or chemical (sodium carbonate peroxyhydrate, SCP) means to generate H2O2. When low levels of thiocyanate (SCN-) were used in the GO system, H2O2 was detected and lactoperoxidase (LP) was inactivated when SCN- was depleted. With 10-fold higher SCN-, LP remained active and H2O2 was not detectable. The oxidation product of the LP reaction, most likely hypothiocyanite, was present in low concentrations. When SCP was used for the immediate generation of H2O2 in a system employing low SCN-, half the LP activity was lost within minutes but thereafter it remained stable. Low concentrations of oxidation product were measured and H2O2 was not detected during the course of the experiment. At high SCN- levels, relatively high concentrations of oxidation product were produced immediately, with H2O2 undetectable. The results suggest that the final product of the LP reaction depends on the method of H2O2 generation and the relative proportions of the substrates. Antibacterial activity of the two LPS was tested against an enterotoxigenic strain of Escherichia coli. Both systems showed bactericidal activity within 4 h incubation at 37 degrees C.

Analyses of salivary components in leukemia patients receiving chemotherapy

We analyzed several salivary components in stimulated whole saliva from patients with acute leukemia who were undergoing chemotherapy. Saliva samples were collected at the time of diagnosis and longitudinally during the treatment period. Data analyses showed that patients with leukemia had significantly higher peroxidase and amylase activity and elevated concentrations of total protein at the time of diagnosis. After induction chemotherapy these parameters returned to normal values and remained constant during the observation period. At the time of diagnosis no significant differences in thiocyanate (SCN-) concentrations were found in saliva samples from control subjects and patients with leukemia. Treatment with cytotoxic agents resulted in granulocytopenia and a concomitant decrease in the SCN- concentration in saliva. The function of the salivary peroxidase system is impaired by the decrease in SCN- concentration, which may be a contributing factor to some of the oral complications that occur in patients undergoing chemotherapy.

Effect of the lactoperoxidase system on Listeria monocytogenes behavior in raw milk at refrigeration temperatures

Activity of raw milk lactoperoxidase-thiocyanate-hydrogen peroxide (LP) system on four Listeria monocytogenes strains at refrigeration temperatures after addition of 0.25 mM sodium thiocyanate and 0.25 mM hydrogen peroxide was studied. The LP system exhibited a bactericidal activity against L. monocytogenes at 4 and 8 degrees C; the activity was dependent on temperature, length of incubation, and strain of L. monocytogenes tested. D values in activated-LP system milk for the four strains tested ranged from 4.1 to 11.2 days at 4 degrees C and from 4.4 to 9.7 days at 8 degrees C. The lactoperoxidase level in raw milk declined during a 7-day incubation, the decrease being more pronounced at 8 degrees C than at 4 degrees C and in control milk than in activated-LP system milk. The thiocyanate concentration decreased considerably in activated-LP system milk at both temperatures during the first 8 h of incubation. LP system activation was shown to be a feasible procedure for controlling development of L. monocytogenes in raw milk at refrigeration temperatures.

Combined inhibitory effect of lactoferrin and lactoperoxidase system on the viability of Streptococcus mutans, serotype c

We have studied the effects of iron-free lactoferrin (apo LF) and lactoperoxidase system (lactoperoxidase, LP/SCN-/H2O2), separately and together, on the viability of Streptococcus mutans (serotype c) in vitro. The bacteria were incubated in buffered KCl (pH 5.5) with and without the above components which were used at concentrations normally present in human saliva. Both apo LF and LP-system had a bactericidal effect against S. mutans at low pH. Together they showed an additive, but not a synergistic, antibacterial effect against S. mutans. Apo LF enhanced the LP enzyme activity but decreased the yield of the antimicrobial component, hypothiocyanite (HOSCN/OSCN-), when incorporated into the reaction mixtures. This decrease, which was most pronounced at low pH, was due to an LP-independent reaction between apo LF and HOSCN/OSCN-. Our study indicates that the LP-system and apo LF can be combined to combat oral S. mutans.

Influence of breed, animal, and days of lactation on lactoperoxidase system components in goat milk

Lactoperoxidase and thiocyanate content in goat milk from two Spanish breeds throughout 5 mo of lactation has been investigated. Mean lactoperoxidase for milk from Verata and Murciano-Granadina goats was .95 and 2.15 units/ml, respectively. Very low concentrations, .03 units/ml for Verata and .20 units/ml for Murciano-Granadina, were found for the first 24 h after kidding. Highest concentrations were detected at the end of lactation (135 to 150 d) for Verata and in midlactation (60 to 75 d) for Murciano-Granadina goats. Mean thiocyanate content was 5.76 ppm for Verata goats, without a distinct maximum throughout lactation, and 3.20 ppm for Murciano-Granadina goats, with maximum levels at final lactation stages. Activation of the lactoperoxidase system might be a useful procedure in preserving raw goat milk quality by addition of low levels of thiocyanate and hydrogen peroxide.

Inhibition of the growth of Streptococcus mutans, Streptococcus sobrinus and Lactobacillus casei by oral peroxidase systems in human saliva

Streptococcus mutans, Strep. sobrinus and Lactobacillus casei were grown in glucose-supplemented, sterilized, human whole saliva, adjusted to pH 5, 6 or 7. Components of the antibacterial peroxidase system--hypothiocyanous acid (HOSCN) and hypothiocyanite ions (OSCN-)--were generated by adding exogenous H2O2 to sterilized saliva containing endogenous peroxidases and thiocyanate (SCN-) ions. HOSCN/OSCN- generation was proportional to the amount of H2O2 added, and more HOSCN/OSCN- was detected in saliva at pH 7 than at pH 5. However, the growth of mutans streptococci and L. casei was inhibited at pH 5 by HOSCN/OSCN-, whereas no inhibition was found at pH 7. The findings show that (a) sufficient amount of HOSCN/OSCN- will inhibit the growth of cariogenic bacteria in human saliva at pH 5; (b) this amount of HOSCN/OSCN- can be generated in saliva by exogenously added H2O2; and (c) peroxidase systems have stronger antistreptococcal effects in human whole saliva than in phosphate buffer.

Quantitative, standardized assays for determining the concentrations of bovine lactoperoxidase, human salivary peroxidase, and human myeloperoxidase

Because of the important biological functions of peroxidases, there is growing interest in the measurement of their concentrations in various secretions. At present, there is no standard method which allows for comparisons in reported activities. This report describes procedures which can be used to measure peroxidase enzyme concentrations by commonly employed assays. Regression equations have been determined which can be used to calculate concentrations of bovine lactoperoxidase (LPO), human salivary peroxidase (SPO), and human myeloperoxidase (MPO) from activities measured with the following donors: pyrogallol, guaiacol, 2,2'-azinobis(3-ethylbenzylthiazoline-6-sulfonic acid), and thiocyanate (SCN-). The peroxidation rates of these donors depend upon the concentrations of hydrogen peroxide (H2O2) used in the individual assays and thus, for accurate, reproducible results, these concentrations must be carefully controlled. The SCN- normally present in human saliva will reduce observed reaction rates by simple competition kinetics in the ABTS, guaiacol and pyrogallol assays and will increase the rates observed when Cl- is used as a donor in NBS assay for MPO. Therefore, SCN- must be removed from saliva samples prior to peroxidase activity determination by all assays except the thionitrobenzoic acid (NBS) assay. LPO cannot be used as a standard for either SPO or MPO because the specific activities of LPO, SPO, and MPO are significantly different.

Inhibition of Listeria monocytogenes growth by the lactoperoxidase-thiocyanate-H2O2 antimicrobial system

The lactoperoxidase-thiocyanate-H2O2 system (LP system), consisting of lactoperoxidase (0.37 U/ml), KSCN (0.3 mM), and H2O2 (0.3 mM), delayed but did not prevent growth of L. monocytogenes Scott A at 5, 10, 20, and 30 degrees C in broth and at 20 degrees C in milk. The net lag periods determined spectrophotometrically varied inversely with temperature and were shorter at 5 and 10 degrees C for cultures from shaken versus from statically grown inocula. Lag periods for cultures from shaken and statically grown inocula, respectively, were 73 and 98 h at 5 degrees C, 22 and 32 h at 10 degrees C, both 8.9 h at 20 degrees C, and both 2.8 h at 30 degrees C. After the lag periods, the maximum specific growth rates were similar for each of the three treatments (complete LP system, H2O2 alone, or control broth) at 5, 10, and 20 degrees C and were 0.06 to 0.08, 0.09 to 0.1, and 0.32 to 0.36/h, respectively. At 20 degrees C in sterile reconstituted skim milk, the LP system restricted growth of Scott A, with log CFU counts per ml at 0, 36, and 68 h being 5.7, 6.4 and 7.9 (versus 5.7, 9.8, and 11.2 for controls). Possible explanations for the decreased lag times observed for cultures from aerobically grown inocula are discussed.