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PubMed2005

A novel selective medium for isolation of Streptococcus mutans.

The aim of this study was to improve the selective medium of Streptococcus mutans. A new selective medium, designated MS-MUTV, was prepared by adding 10 mg/l valinomycin to the MS-MUT medium previously described. The average recovery of S. mutans was 72.1%, and the growth of S. sobrinus and S. anginousus group was inhibited on MS-MUTV, but allowed on MS-MUT. One hundred and thirty-nine human saliva samples were examined and counted for S. mutans and non-S. mutans colonies. The recovery of S. mutans on MS-MUTV was similar to that on MS-MUT. Eighty-two and 7.9 percent of the saliva samples obtained S. mutans pure cultures, with no bacterial growth on MS-MUTV, respectively. The remaining 10.1% were contaminated with non-S. mutans, with low-level CFU. MS-MUTV is useful for the isolation of S. mutans alone from clinical samples in routine examinations.

Bacteriological Techniques↗

PubMed2002

Influences of orthodontic appliances on oral populations of mutans streptococci.

A study was conducted to assess the influence of fixed appliances on the mutans streptococcal in a group of patients receiving orthodontic treatment. Mutans streptococcal counts in stimulated saliva of 27 patients were obtained at baseline, and at 1-month intervals for 4 months. The difference in mutans streptococcal counts at baseline and at the 4-month sampling was less than an order of magnitude in 18 of the patients, between 1 and 2 orders of magnitude in eight of the patients, and 3 orders of magnitude in one patient. Restriction endonuclease digests of genomic DNA from representative mutans streptococci isolates taken from baseline and 4-month saliva samples, as well as from 4-month tooth and appliance surfaces, were examined by pulsed field gel electrophoresis, after restriction endonuclease digestion. Results of the DNA banding patterns associated with isolates from 19 patients showed that, for 12 patients, all isolates examined represented the same clone of Streptococcus mutans, whereas for six patients two different S. mutans clones were detected. One patient yielded three different clones of S. mutans. A much larger number of baseline, as well as post-appliance, isolates will have to be examined from each patient in future studies, in order to determine if the number of different S. mutans clones harbored by individual patients is related to orthodontic treatment.

Adolescent↗

PubMedDate not supplied

Inhibitory effects of MoAbs against a surface protein antigen in real-time adherence in vitro and recolonization in vivo of Streptococcus mutans.

A surface protein antigen (PAc) of Streptococcus mutans, particularly the A-region of the molecule, has been reported to interact with salivary components on the tooth surface. It might be a candidate antigen inducing the production of antibodies against the adherence of S. mutans to the tooth surface. We investigated the effects of monoclonal antibodies (MoAbs) obtained by immunization of synthetic PAc peptides that completely correspond to the amino acid sequence of part of the A-region. These MoAbs recognize several core B-cell epitopes in the sequence. Two (KH5 and SH2) of these antibodies reacted with both S. mutans and Streptococcus sobrinus, but not with Streptococcus sanguis, Streptococcus salivarius, Porphyromonas gingivalis or Lactobacillus casei. They clearly inhibited the real-time adherence of S. mutans to salivary components in a biosensor. KH5, which showed a real-time inhibition (71%), also significantly prevented the recolonization of S. mutans on the tooth surface in rats. These results suggested that the core B-cell epitope (-Y---L--Y----) recognized by KH5 was the essential sequence in the antigenic epitopes of PAc protein recognized specifically by the inhibitory antibody. Therefore, the amino acid residues were found to be important in the initial attachment of S. mutans to the tooth surface. These results provide for the mechanism of PAc molecule in the initial attachment of S. mutans on the tooth surface and more effective designs for the removal of S. mutans and S. sobrinus from the oral cavity.

Adhesins, Bacterial↗

PubMed2000

Identification of mutans and other oral streptococci by random amplified polymorphic DNA analysis.

The identification and classification of the non-haemolytic or viridans group of streptococci have long been recognised as difficult and unsatisfactory. Phenotypic and genotypic heterogeneity have resulted in ambiguous speciation, particularly with mutans streptococci and other oral streptococci. This study was done to determine whether random amplified polymorphic DNA (RAPD) analysis is useful to identify and even classify oral and other streptococci. DNA was prepared and purified from 25 strains of mutans streptococci including 11 reference strains of Streptococcus mutans, seven of S. sobrinus, three of S. rattus and one each of the four other species of the mutans group, together with 20 other reference species, mostly streptococci, and from 49 fresh isolates of mutans streptococci and of S. mutans from human saliva and dental plaque. DNA amplification was primed with each of three arbitrarily selected primers nine or 10 nucleotides in length. The amplified DNA fragments (amplicons) obtained were compared by agarose gel electrophoresis. Species- and strain-specific RAPD fingerprints were obtained not only from pure genomic DNA, but also from the supernates of crude cellular or colony extracts. Pending the analysis of numerous other strains, the data suggest that RAPD may be of value: (i) to distinguish the species S. mutans and S. sobrinus from each other and potentially from other species of oral streptococci, (ii) to differentiate and possibly classify oral streptococci and (iii) as a valuable tool in mutans streptococci epidemiology and transmission studies, by virtue of its rapidity, efficiency and reproducibility in generating genetic fingerprints of streptococcal isolates.

Adult↗

PubMed2000

The mannitol-specific enzyme II (mtlA) gene and the mtlR gene of the PTS of Streptococcus mutans.

The phosphoenolpyruvate-dependent phosphotransferase system (PTS) is widely found among Gram-positive bacteria. It is the major source of carbohydrate transport in the dental pathogen Streptococcus mutans. The transported carbohydrates are fermented to produce large amounts of lactic acid which initiates dental caries. The authors have isolated the S. mutans gene for the mannitol-specific Enzyme II (EII) component of the PTS, mtlA, and the adjacent mtlR gene, which is located in the same operon. The mtlR gene is located between mtlA and the genes mtlF and mtlD. The nucleotide sequence of the mtlA and mtlR loci has been determined. The deduced mtlA gene product of S. mutans consists of 589 amino acids with a molecular mass of 62.0 kDa. It exhibits similarity with the mtlA gene products from other organisms. However, the similarity between these proteins is generally restricted to the 470 amino-terminal residues of the S. mutans protein. This region would correspond to the EIICB domains of the PTS. The authors have previously shown that the S. mutans mtlF gene product exhibits 76.6% similarity to the carboxyl-terminal 143 amino acids of the Escherichia coli mtlA product and that the mtlF gene encodes the EIIA domain of the PTS. Thus, the genes that encode the EIICB and the EIIA domains are separated by approximately 2250 bp. In many organisms, all of the EII domains may be fused together to form one molecule. The fact that these domains are separated by this distance in S. mutans supports the hypothesis that various functional domains of the PTS have been rearranged during evolution. The sequence of the 119 carboxyl-terminal amino acids of the S. mutans mtlA gene product also displays homology to the carboxyl-terminal end of the EIIB domain of various mannitol PTSs. Thus, this domain may have been duplicated in S. mutans during evolution of the operon. The mtlR gene is located in the same operon structure as mtlA but these loci are separated by an intragenic space. The precise 5' end of the mtlR locus cannot be determined either by in vitro transcription-translation assays or based upon nucleotide sequence analysis because of the apparent lack of a ribosome-binding site preceding the gene. The deduced mtlR gene product, which consists of approximately 650 amino acids with a molecular mass of 75.3 kDa, exhibits limited similarity to several potential transcriptional regulators. However, the exact function of this locus is currently unknown.

Amino Acid Sequence↗

PubMed1982

Immunisation of rhesus monkeys with Streptococcus mutans, Lactobacillus acidophilus and lipoteichoic acid for protection against dental caries.

An attempt was made to protect rhesus monkeys from dental caries by immunisation with Streptococcus mutans, Lactobacillus acidophilus and lipoteichoic acid (LTA). The vaccine composed of S. mutans gave significant protection against caries, a decrease in the number of S. mutans, an increase in IgG antibodies and a moderate increase in complement-fixing antibodies to LTA. When LTA was used as immunogen, there was only a small reduction in caries, without any detectable antibodies to LTA and a slight increase in IgG antibodies to cell of S. mutans. Vaccines of L. acidophilus or L. fermentum gave no protection. A combined vaccine of S. mutans and L. acidophilus did not reduce the incidence of caries but the antibody titre to cells of S. mutans was raised to a level comparable with that in the S. mutans-immunised monkeys. The results of this investigation in a subhuman primate confirm that immunisation with S. mutans induces protection against caries, unlike the attempt to immunise with two selected strains of lactobacilli. More studies are required to establish the role of specific serotypes of lactobacilli in the development of dental caries.

Animals↗

PubMed1983

Effective immunity to dental caries: protection of gnotobiotic rats by local immunization with a ribosomal preparation from Streptococcus mutans.

A ribosomal preparation from Streptococcus mutans 6715 was characterized for its ability to induce an immune response in gnotobiotic rats which was protective against S. mutans-induced dental caries. Animals injected in the salivary gland region with the S. mutans ribosomal vaccine developed significantly higher (P less than 0.01) salivary IgA and serum IgG antibody activities against whole S. mutans cells and ribosomal preparations than nonimmunized rats. Vaccinated animals had significantly lower (67%; P less than 0.01) levels of S. mutans adherent to their molar surfaces than the control rats after infection with the homologous, cariogenic S. mutans. The immunized animals had significantly fewer (P less than 0.01) carious lesions on their buccal, sulcal, and proximal molar surfaces than the nonimmunized rats following challenge with the virulent organism. Animals injected with the ribosomal preparation developed salivary IgA and IgG antibodies with specificities to various cell surface-associated antigens such as lipoteichoic acid and glucosyltransferase, suggesting that the observed protection may be due to antibodies against cell surface contaminants of the ribosomal vaccine. These results are the first demonstration that a ribosomal preparation from S. mutans protected rats from caries formation after challenge with the homologous, virulent S. mutans.

Animals↗

PubMed1996

Rapid identification of mutans streptococcal species.

Mutans streptococci are considered the predominant pathogens in dental caries. Three methods, i.e. dot blot hybridization analysis, PCR analysis and SDS-blue dextran-PAGE, were examined for identifying mutans streptococcal species. In dot blot hybridization, DNA probe derived from the dextranse gene (dexA) of Streptococcus mutans hybridized with different intensities under the condition of low stringency against each species of mutans streptococci although the dexA probe was specific for S. mutans under the condition of high stringency. Oligonucleotide primers for polymerase chain reaction (PCR) were designed on the basis of the dexA DNA sequence. The primers amplified species-specific PCR products in the reference species (15 strains of 5 species) of mutants streptococci. An electrophoretic profile of dextranases from the mutans streptococci on SDS-blue dextran-PAGE also showed species-specific behavior. These results suggest that the three identification methods examined here are useful for distinguishing the species of mutans streptococci and also indicate that PCR analysis is suitable for simple, rapid and reliable identification of mutans streptococcal species.

Bacterial Typing Techniques↗

PubMed1998

Genotyping shows different strains of mutans streptococci between father and child and within parental pairs in Swedish families.

The purpose of this study was to investigate whether there was an intrafamilial similarity of mutans streptococcal strains in some Swedish families using chromosomal DNA fingerprinting. Plaque samples were obtained from buccal and occlusal surfaces of 25 three-year-old children, their mothers and 18 fathers. The colonization levels of mutants streptococci were estimated with the "Strip mutans" test, and caries experience was scored by decayed, missing and filled teeth or decayed, extracted and filled teeth. Interviews about medical history, diet regimes, breastfeeding and care of the child were performed. In 11 families isolates of mutans streptococci were detected in all three individuals. These isolates were serotyped by immunofluorescent technique and genotyped using the restriction endonuclease Hae III. The results showed that 5 children harbored mutans streptococci genotypes different from their parents. Six children showed genotypes identical to their mothers. None of the children harbored genotypes similar to their fathers, even though two thirds of the fathers had high or very high mutans streptococci levels. No matching of genotypes was observed within the 11 parental pairs. Mothers as primary caregivers with high "Strip mutans" scores were more often observed in the group with identical genotypes within the mother-child pairs, the "matching group", than in the "no-matching group". These data indicate that the fathers and the children had not acquired each others' strains of mutans streptococci nor had the spouses. The results suggest that the children acquired mutans streptococci both from outside and inside the family.

Adult↗

PubMed1982

Transient reduction of Streptococcus mutans interdentally by chlorhexidine gel.

Chlorhexidine gel was applied interproximally with the intent to reduce Streptococcus mutans at these sites. Bacterial samples were obtained using toothpicks, which were inserted in each interproximal space and then immediately pressed against agar plates, selective for S. mutans. Duplicate bacterial samples of non-treated subjects showed that this method gave reproducible results. Using a split mouth technique, 10 subjects were exposed to short term chlorhexidine exposures of varied intensity. At the baseline sampling about 90% of the sites showed growth of S. mutans. One week after the chlorhexidine applications about 55% were infected. After 40 d S. mutans were back to about baseline levels except for the most intensively treated interproximals, which showed 75% infected sites. Thus, at many sites the reduction of S. mutans was only transient. Four subjects with more than 1 million S. mutans per ml saliva participated in a study where salivary and interproximal levels of S. mutans were compared after a rinsing period with chlorhexidine lasting for 2 weeks. The effect of the rinses varied individually, but it was noted that several interproximal spaces could be infected even if the saliva numbers did not reach detectable levels of S. mutans.

Chlorhexidine↗

PubMed1988

Prevalence of mutans streptococci and lactobacilli in elderly Swedish individuals.

The number of Streptococcus mutans, Streptococcus sobrinus, and lactobacilli in stimulated whole saliva was examined in 149 elderly persons. More than 10(6) CFU/ml of mutans streptococci were found in 57% of the subjects and 85% had more than 10(5) lactobacilli per ml of saliva. There was no difference in the prevalence of mutans streptococci between edentulous and dentate subjects whereas significantly more lactobacilli were detected in denture wearers. S. mutans was most frequent and was found in 72% of the subjects. S. sobrinus, which was carried by 44% of the persons, was found proportionally in more subjects with dentures than in dentate individuals. In most persons with S. sobrinus, S. mutans was also present but in 8% of the subjects only S. sobrinus was detected. The subjects with both S. mutans and S. sobrinus had higher salivary levels of mutans streptococci than individuals with only S. mutans or S. sobrinus.

Aged↗

PubMed1995

The toothpick method in relation to other plaque sampling techniques for evaluating mutans streptococci.

The aim of the present study was to compare the use of toothpicks with other sampling methods for determination of mutans streptococci on different tooth surfaces. In nine persons with > 10(5) CFU per ml saliva of mutans streptococci, plaque samples were taken from 90 buccal and lingual surfaces, 108 occlusal surfaces and 90 approximal surfaces with toothpicks. The prevalence of mutans streptococci on these tooth surfaces was compared with samples taken at four 1-week intervals on the same tooth surfaces with a carver (buccal/lingual surfaces), a needle (occlusal surfaces) or a dental floss (approximal surfaces). Each sample was plated on MSB agar and the presence of mutans streptococci was expressed on a scale varying from 0 to 4. On two of the sampling occasions the amount of plaque, mirrored by total viable counts on blood agar, was also determined. Only for buccal/lingual plaque samples was a difference in total counts between methods noted and then with higher total recoveries obtained after sampling with toothpicks. More surfaces were found to be positive for mutans streptococci when samples were taken with a toothpick than with a carver, needle or floss. On surfaces positive for mutans streptococci the colonization score was higher in samples taken with a toothpick than with a carver or a needle while samples taken with a floss showed a tendency to higher levels of mutans streptococci than samples collected with a toothpick. The data indicate that the results indicate that the results obtained by using toothpicks for evaluating the prevalence of mutans streptococci on individual tooth surfaces compare favorably with the other methods tested.

Adult↗

PubMed1996

Plaque fluoride and mutans streptococci in plaque and saliva before and after discontinuation of water fluoridation.

Our aim was to compare plaque fluoride and the level of mutans streptococci in saliva and plaque before and 1 and 2 years after discontinuation of water fluoridation in Kuopio, Finland. For comparison, a low-fluoride community was included in the study. Pooled plaque and saliva were collected from a random sample of 12-year-olds in both communities (n = 139). Enumeration of mutans streptococci in plaque was made on MSB agar and the level of salivary mutans streptococci was measured using the Strip mutans method. Fluoride was analyzed using a fluoride specific electrode. Caries, gingival status, fluoride varnish applications and self-reported oral health habits were recorded at baseline. Before discontinuation of fluoridation, the level of mutans streptococci in saliva was significantly lower in the fluoridated than in the non-fluoridated community. The difference in plaque mutans streptococci was not statistically significant. After discontinuation of water fluoridation, there was a significant shift towards elevated values of salivary mutans streptococci in the fluoridated community, but the level of mutans streptococci in plaque remained at the baseline level. There was no significant difference between the communities in the fluoride content of plaque either before or after discontinuation of fluoridation. From the background factors, only caries scores (higher in the non-fluoridated community) and oral hygiene (better in the non-fluoridated community) were significantly different between the communities.

Chewing Gum↗

PubMed1999

Interactions of Streptococcus mutans fimbria-associated surface proteins with salivary components.

Streptococcus mutans has been implicated as the major causative agent of human dental caries. S. mutans binds to saliva-coated tooth surfaces, and previous studies suggested that fimbriae may play a role in the initial bacterial adherence to salivary components. The objectives of this study were to establish the ability of an S. mutans fimbria preparation to bind to saliva-coated surfaces and determine the specific salivary components that facilitate binding with fimbriae. Enzyme-linked immunosorbent assay (ELISA) established that the S. mutans fimbria preparation bound to components of whole saliva. Sodium dodecyl sulfate-polyacrylamide gel electrophoresis (SDS-PAGE) and Western blot techniques were used to separate components of whole saliva and determine fimbria binding. SDS-PAGE separated 15 major protein bands from saliva samples, and Western blot analysis indicated significant binding of the S. mutans fimbria preparation to a 52-kDa salivary protein. The major fimbria-binding salivary protein was isolated by preparative electrophoresis. The ability of the S. mutans fimbria preparation to bind to the purified salivary protein was confirmed by Western blot analysis and ELISA. Incubation of the purified salivary protein with the S. mutans fimbria preparation significantly neutralized binding of the salivary protein-fimbria complex to saliva-coated surfaces. The salivary protein, whole saliva, and commercial amylase reacted similarly with antiamylase antibody in immunoblots. A purified 65-kDa fimbrial protein was demonstrated to bind to both saliva and amylase. These data indicated that the S. mutans fimbria preparation and a purified fimbrial protein bound to whole-saliva-coated surfaces and that amylase is the major salivary component involved in the binding.

Amylases↗

PubMed1981

Role of interbacterial adherence in colonization of the oral cavities of gnotobiotic rats infected with Streptococcus mutans and Veillonella alcalescens.

The role of interbacterial adherence in the colonization of the rate oral cavity was investigated with aggregating and nonaggregating strains of Veillonella alcalescens and Streptococcus mutans. V. alcalescens V-1 and S. mutans M-7 rapidly formed large stable aggregates when mixed in vitro. Aggregates could be reduced in size by sonication, but they could not be completely dispersed, indicating that bonding between the organisms was strong. V. alcalescens V-1 did not coaggregate with S. mutans C67-1, and V. alcalescens OMZ193 did not coaggregate with either S. mutans strain C67-1 or M-7. Osborne-Mendel rats monoassociated with either S. mutans C67-1 or M-7 were inoculated with veillonellae, molar teeth were removed at 2 h and at 14 days, and the number of veillonellae was determined. At 2 h post-inoculation there were 600 times as many colony-forming units of V. alcalescens V-1 adherent to the teeth of animals monoassociated with S. mutans M-7 when compared with animals monoassociated with the nonaggregating S. mutans C67-1. The number of colony-forming units of V. alcalescens V-1 was 1,000 times greater than the number of nonaggregating V. alcalescens OMZ193 in S. mutans M-7-infected animals. Similar results were obtained when teeth were samples 14 days after inoculation. Veillonellae inoculated into the mouths of germfree animals rapidly disappeared from tooth surfaces.

Animals↗

PubMed1982

Glucose uptake by Streptococcus mutans, Streptococcus mitis, and Actinomyces viscosus in the presence of human saliva.

Glucose uptake was examined by using whole-cell suspensions of Streptococcus mutans (strains BHT, Ingbritt, and GS-5), Streptococcus mitis (strains 9811 and 72x41), and Actinomyces viscosus (strains T6 and WVU626) incubated for up to 90 min in 0 to 82% (vol/vol) human whole salivary supernatant. Glucose uptake by the S. mutans strains was completely inhibited at all saliva concentrations. Dithiothreitol (DTT), present during saliva incubation, prevented saliva inhibition. Glucose uptake was also restored when saliva-inhibited cells were subsequently exposed to DTT. The inclusion of catalase in the saliva incubation mixtures resulted in protection equal to that obtained with DTT. The S. mitis strains were also inhibited by saliva but to a far lesser extent that S. mutans. DTT and catalase also protected S. mitis from saliva inhibition. Both A. viscosus strains were completely refractory to saliva inhibition of glucose uptake. Based on (i) the sensitivity of the catalase-negative streptococci and the resistance of catalase-positive actinomyces to saliva inhibition and (ii) the equal and complete protection to saliva inhibition afforded by DTT and catalase, we conclude that the lactoperoxidase-SCN(-)-H(2)O(2) system in saliva was the only antibacterial system expressed under our experimental conditions. The relative resistance of S. mitis 9811 (compared with S. mutans BHT) to saliva inhibition was shown not to result from poor H(2)O(2) production in either glucose-supplemented buffer or saliva solutions. S. mitis produced inhibitory quantities of H(2)O(2) that equaled or exceeded S. mutans H(2)O(2) accumulation. It is suggested that S. mitis might possess a greater ability to repair lactoperoxidase-mediated damage than does S. mutans. Every organism studied exhibited a saliva concentration-dependent, cell growth-independent stimulation of glucose uptake after 60 to 90 min of incubation. The A. viscosus and S. mitis strains showed saliva stimulation (or stabilization) of glucose uptake with unsupplemented saliva. In the case of S. mutans, saliva stimulation was only observed when DTT was present. The possible role of salivary lactoperoxidase as a modulator of the intraoral site specificities exhibited by S. mutans is discussed.

Actinomyces↗

PubMed1983

Effective immunity to dental caries: gastric intubation of Streptococcus mutans whole cells or cell walls induces protective immunity in gnotobiotic rats.

Gnotobiotic rats were given Streptococcus mutans 6715 whole cells (WC), purified cell walls (CW), or cell wall lysate by gastric intubation (GI), and assessments were made of humoral immune responses in serum and saliva and of caries protection. Levels of secretory immunoglobulin A (IgA) and IgG antibodies to S. mutans WC in saliva samples from experimental rats were determined by an enzyme-linked immunosorbent assay. Serum antibody levels of the IgM, IgG, and IgA isotypes were also determined. Similar levels of salivary antibodies were induced in rats given S. mutans WC or CW by GI, whereas lower salivary antibody titers were observed in rats given cell wall lysate by the oral route. The level of serum antibodies in the various groups of rats also reflected the oral antigen used. The specificity of salivary IgA and serum IgG antibodies in the various groups of rats was determined by enzyme-linked immunosorbent assay with lipoteichoic acid, serotype g carbohydrate, dextran, CW, and WC as coating antigens. Salivary IgA and serum IgG antibodies in rats given S. mutans WC or CW by GI were primarily directed to lipoteichoic acid and serotype g carbohydrate. The presence of salivary IgA antibodies to S. mutans in rats given either S. mutans WC or CW by GI correlated with a significant reduction in the levels of plaque, numbers of viable S. mutans in plaque, and caries scores when compared with the control animals (infected only). These results demonstrate that particulate antigens of S. mutans induce salivary immune responses when given by GI to gnotobiotic rats and that the presence of these antibodies correlates with caries protection.

Animals↗

PubMed1984

Growth-inhibitory and bactericidal effects of human parotid salivary histidine-rich polypeptides on Streptococcus mutans.

Growth inhibition and cell viability assays demonstrate that the histidine-rich polypeptides isolated from human parotid saliva are bacteriostatic and bactericidal for strains of Streptococcus mutans belonging to the serotype b and c classifications. Both inhibition of growth and cell division are enhanced by preincubation of bacteria with these polypeptides in low-ionic-strength buffers of acidic and neutral pH before dilution into enriched growth media. With prior exposure at pH 6.8, inhibition by these polypeptides of the serotype c strains, S. mutans GS5 and SB, as well as the serotype b strain, S. mutans BHT, is reversible over time under the experimental conditions selected. With similar exposure at pH 5.2, however, irreversible damage is manifested by complete inhibition of both growth and cell viability. At concentrations of 250 micrograms of the mixture of histidine-rich polypeptides per 5 X 10(5) bacterial cells per ml in the acidic preincubation buffer, bacterial lethality is maintained for a period of 48 h in the enriched growth media. At a 50-micrograms/ml concentration of these salivary agents, approximately 80% killing of S. mutans SB is noted after a 24-h incubation; however, surviving bacteria multiply and reach turbidities of untreated control cells when examined at the 48-h growth point. Similarly, hen egg white lysozyme is also found to be bactericidal for these microorganisms when preincubation is carried out under acidic conditions. However, in contrast to the histidine-rich polypeptides, lysozyme under these experimental conditions does not inhibit growth of S. mutans SB at neutral pH, although it does inhibit growth of both S. mutans BHT and S. mutans GS5 at this pH. Preexposure of S. mutans SB to the peptides in buffer at ionic strengths of 0.025 to 0.125, followed by either viability assays under nongrowing conditions or growth inhibition studies, suggests that there is very little effect of ionic strength on the antibacterial function of these peptides. In contrast to the inhibition of viability noted under growing conditions, lower concentrations of the histidine-rich polypeptides were required to elicit immediate cell death under nongrowing conditions.

Acetates↗