Oxazolidinones mechanism of action: inhibition of the first peptide bond formation

Oxazolidinones are potent inhibitors of bacterial protein biosynthesis. Previous studies have demonstrated that this new class of antimicrobial agent blocks translation by inhibiting initiation complex formation, while post-initiation translation by polysomes and poly(U)-dependent translation is not a target for these compounds. We found that oxazolidinones inhibit translation of natural mRNA templates but have no significant effect on poly(A)-dependent translation. Here we show that various oxazolidinones inhibit ribosomal peptidyltransferase activity in the simple reaction of 70 S ribosomes using initiator-tRNA or N-protected CCA-Phe as a P-site substrate and puromycin as an A-site substrate. Steady-state kinetic analysis shows that oxazolidinones display a competitive inhibition pattern with respect to both the P-site and A-site substrates. This is consistent with a rapid equilibrium, ordered mechanism of the peptidyltransferase reaction, wherein binding of the A-site substrate can occur only after complex formation between peptidyltransferase and the P-site substrate. We propose that oxazolidinones inhibit bacterial protein biosynthesis by interfering with the binding of initiator fMet-tRNA(i)(Met) to the ribosomal peptidyltransferase P-site, which is vacant only prior to the formation of the first peptide bond.

Alpha(v)beta(3) integrin in angiogenesis and restenosis

Various integrins are thought to be intimately involved in several pathological processes, including cancers (solid tumors and metastasis), cardiovascular diseases (stroke and heart failure), inflammatory diseases (rheumatoid arthritis) and ocular pathologies. The mechanism of the involvement of integrins in these acute and chronic disease states is slowly being elucidated. Recently, various therapeutic candidates, including antibodies, cyclic peptides and peptidomimetics, have been clinically evaluated and have been shown to successfully modulate certain disease processes. This review focuses on the key role of the alpha(v) integrin (alpha(v)beta(3)) in the angiogenic processes in diseases such as cancer, restenosis following percutaneous transluminal coronary angioplasty, stroke, ocular disease and rheumatoid arthritis.

Regulation of gene expression and cell growth in vivo by tetracycline using the hollow fiber assay

The hollow fiber assay presents a potentially unique tool to study the effects of regulated gene expression in cell lines that do not form tumors in vivo. The hollow fibers allow small molecules to pass freely through while keeping the cells within the fibers and segregated from host cells. OSp16.1 cells, derived from the U24 clone of the U2-OS osteogenic sarcoma tumor line, express the p16INK4a tumor suppressor under the regulation of tetracycline (tet) (Mitra J et al. Mol Cell Bio 19:3916, 1999). The in vitro induction of p16 in the OSp16.1 cell line is regulated by tet. The hollow fiber assay was used to determine whether the regulation of the p16 gene could be achieved in vivo, since these cells did not grow in the xenograft model. There were no differences in the in vivo growth pattern of U24 cells loaded into the hollow fibers with and without tet: 807% and 839% net growth, respectively. OSp16.1 cells in fibers in mice receiving 3.33 mg/kg/day tet had a 644% net growth after 21 days. There was a 194% net growth without tet. Immunoblotting of extracts prepared from the hollow fibers confirmed that p16 was induced in the absence of tet. These data demonstrate this assay is a useful tool for studying the effects of regulated gene expression in vivo.

Nonpeptide factor Xa inhibitors II. Antithrombotic evaluation in a rabbit model of electrically induced carotid artery thrombosis

SK549 (mol. wt. 546 Da) is a synthetic, selective inhibitor of human coagulation factor Xa (fXa) (K(i) = 0.52 nM). This study compared the antithrombotic effects of SK549 and a series of benzamidine isoxazoline fXa inhibitors with aspirin, DuP 714 (a direct thrombin inhibitor), recombinant tick anticoagulant peptide, or heparin in a rabbit model of electrically induced carotid arterial thrombosis. Compounds were infused i.v. continuously from 60 min before electrical stimulation to the end of the experiment. Values of ED(50) (dose that increases the carotid blood flow to 50% of the control) were 0.12 micromol/kg/h for SK549, 0.56 micromol/kg/h for aspirin, 0.14 micromol/kg/h for DuP 714, 0.06 micromol/kg/h for recombinant tick anticoagulant peptide, and >100 U/kg/h for heparin. The EC(50) (plasma concentration that increased blood flow to 50% of the control) for SK549 was 97 nM. Unlike aspirin and heparin, SK549 was efficacious and, at 1.5 micromol/kg/h i.v. (n = 9), maintained carotid blood flow at 87 +/- 6% of control level for greater than 90 min. Unlike heparin, SK549 inhibited ex vivo fXa activity but not ex vivo thrombin activity. There was a highly significant correlation between K(i) (fXa) and ED(50) of a series of fXa inhibitors (r = 0. 85, P <.001). Therefore, these results suggest that SK549 is a novel, potent, and effective antithrombotic agent in a rabbit model of arterial thrombosis. It is likely that SK549 exerts its antithrombotic effect through selective inhibition of fXa. Furthermore, SK549 may be clinically useful for the prevention of arterial thrombosis.

Tumor biology: use of tiled images in conjunction with measurements of cellular proliferation and death in response to drug treatments

Tumor growth is dependent on the balance between cell proliferation and cell death, and these events occur heterogenously within an individual tumor. We present a methodology that provides integrative information about cell kinetics, cell death, and cell growth within individual tumors in animals treated with cytotoxic chemotherapeutic agents. Using HCT-116 and NCI-H460 cells, human colonic adenocarcinoma and non-small cell lung cells, respectively, traditional xenograft studies were performed. The tumor-bearing animals were treated with cyclophosphamide (Cytoxan), gemcitabine (Gemzar), or mitomycin C, and extensive analysis of the tumors was studied. Cell kinetics were evaluated by measuring the apoptotic and proliferation indices. The ability to image an entire tumor section using "tiling" by creating a large montage from many high-resolution images makes it possible to identify regional differences within areas of tumor and to demonstrate differences in these tumor regions after treatment with selected chemotherapeutic agents. Two specific areas within tumors have been identified: (a) areas of viable cells within the cell cycle, determined by bromodeoxyuridine and/or morphological characteristics determined by hematoxylin staining; and (b) areas of necrosis determined by the absence of bromodeoxyuridine and proliferating cell nuclear antigen-labeled cells coupled with morphological changes. By standardizing the tumor size to 100 mm2, different patterns of tumor responses to chemotherapeutic agents were determined. By creating such tiled images and by quantitating cell cycle kinetics, it is possible to gain a more complete understanding of tumor growth and response to treatment, leading to the development of more reliable methods for assessing the clinical behavior of anticancer drugs.

Small molecule alpha(v) integrin antagonists: novel anticancer agents

The members of the integrin family are targets that potentially provide both therapeutic and diagnostic opportunities. Advances in the understanding of the signalling pathways, transcriptional regulation and the structure/function relationships of the adhesion molecules to extracellular matrix proteins have all contributed to these opportunities. The role of the integrins in pathological processes in both acute and chronic diseases, include ocular, cancer (solid tumours and metastasis), cardiovascular (stroke and heart failure) and inflammatory (rheumatoid arthritis) conditions. Various therapeutic candidates, including antibodies, cyclic peptides and peptidomimetics, have been identified. This review will focus on the key role of the alpha(v) integrin (alpha(v)beta(3) and alpha(v)beta(5)) in angiogenic processes in tumours, including its potential use in cancer diagnostics and therapy.

The hollow fiber assay: continued characterization with novel approaches

The hollow fiber assay, a unique in vivo model, permits the simultaneous evaluation of compound efficacy against multiple cell lines in two physiological compartments. This assay has been used to characterize in vivo activity of cytotoxic compounds. The purpose of the present study was to characterize and optimize this assay for compounds with a defined mechanism of action, specifically cell cycle inhibition. Two human tumor cell lines and one normal human cell line were loaded into polyvinylidene fluoride hollow fibers at two or more cell concentrations and grown in mice for 3-10 days. The data demonstrate the importance of characterizing the initial loading density of various cell lines in the evaluation of compounds. All studies were performed with cells in the linear part of the cell growth curves. Initial loading densities of 1-2 x 10(4) cells/fiber gave the greatest opportunity for growth in the three human cell lines tested (HCT116 colon carcinoma, NCI-H460 non-small cell carcinoma, and AG 1523 normal fibroblast). Utilizing the MTT assay, standard curves were constructed to correlate the final number of cells with optical density (OD) readings at 540 nm in order to calculate cell numbers in the fibers. Insights into the mechanism of action of cisplatin have been gained using Western blot analysis of the cell cycle markers PCNA (a protein present throughout the cell cycle) and Rb (a protein that acts as a tumor suppressor gene product) from the hollow fiber cells. In cisplatin-treated NCI-H460 cells both PCNA and Rb phosphorylation decreased, suggesting the arrest of the cells prior to the S phase. Standard therapeutic agents, cisplatin, racemic flavopiridol, cyclophosphamide and mitomycin C, were evaluated independently in the hollow fiber assay and the xenograft model. The data demonstrate that compounds active in the hollow fiber assay are also active in the xenograft.

Novel small molecule alpha v integrin antagonists: comparative anti-cancer efficacy with known angiogenesis inhibitors

Recent evidence supports the involvement of integrins in angiogenesis: blockade of alpha v beta 3 and alpha v beta 5 integrins disrupts angiogenesis leading to decreased blood vessel formation and hence decreased tumor growth. We hypothesized that av antagonists could inhibit tumor growth in tumor cells devoid of alpha v beta 3 integrins. We evaluated SM256 and SD983, novel small molecules that are specific av antagonists in mouse models of angiogenesis and tumorigenesis, and compared them with standards: TNP470, a fumagillin analog in the clinic, and flavopiridol, a cell cycle kinase inhibitor. In vitro SM256 was a selective alpha v beta 3 inhibitor with an IC50 = 4nM, and the affinity of SD983 against the mouse endothelial alpha v beta 3 integrin yielded an IC50 = 2nM and an IC50 = 54nM against alpha v beta 5. In the mouse Matrigel model of angiogenesis SM256 decreased blood vessel formation (hemoglobin content) with an ED50 = 0.055 ug/kg/day, tenfold more potent than TNP470. SG545, an ester of SD983, decreased blood vessel formation with an ED50 = 6 ug/kg/day, while flavopiridol ED50 = 18 ug/kg/day. In the mouse xenograft model, using human colon carcinoma RKO cells that do not express alpha v beta 3 but express alpha v beta 5, tumor growth was inhibited by SG545 (10 mg/kg/day) and flavopiridol (5 mg/kg/every other day) 40% and 70%, respectively (p < 0.05). Although the proliferative index (measured by BrdU incorporation) was not significantly changed with SM256, SG545 or flavopiridol (29-32%), the apoptotic index increased significantly (p < 0.05) in the SM256 and SG545-treated groups (2.3-2.7%) compared with controls (1.1%), suggesting increased cell death contributed to decreased tumor volumes. Neovascularization decreased with SM256 and SG545 treatment. The data demonstrate that potent selective av antagonist can target endothelial cells, tumor cells, inhibit angiogenesis and inhibit tumor growth.

Antiplatelet efficacy of XV459, a novel nonpeptide platelet GPIIb/IIIa antagonist: comparative platelet binding profiles with c7E3

Recent advances in the development of i.v. platelet glycoprotein alphaIIb/beta3 integrin (GPIIb/IIIa) antagonists led to the development of either a class of small-molecular-weight antagonists with a short to ultra-short duration of antiplatelet effects (Integrelin, Tirofiban, DMP728) or a very long-acting antagonist (ReoPro). Thus the present study was undertaken to characterize the antiplatelet efficacy of a small-molecule GPIIb/IIIa antagonist, DMP754/XV459, and to determine its platelet GPIIb/IIIa receptor binding profiles. DMP754, upon its conversion with esterases to its free acid form XV459, and XV459 itself, demonstrated high potency (IC50 = 0.030-0.060 microM) in inhibiting human platelet aggregation induced by ADP (100 microM), thrombin receptor agonist peptide (10 microM) or collagen (20 microgram/ml) in citrate or heparin. Maximal platelet aggregation inhibition was achieved at 50 to >/=80% receptor occupancy, depending on the agonist used. Both XV459 and c7E3 bind with high affinity to either activated human platelets (Kd = 0.0008 and 0.0091 microM, respectively) or unactivated human platelets (Kd = 0.0025 and 0.0092 microM, respectively). XV459 demonstrated tight association with human, baboon and (to a lesser extent) canine platelets (t1/2 of dissociation = 7 +/- 0, 8 +/- 1 and 1.4 +/- 0.1 minutes, respectively). Both c7E3 and XV459 associate tightly with slower dissociation rates to unactivated human platelets. XV459 represents a potent antiplatelet agent in inhibiting platelet aggregation along with offering high affinity and a relatively slow dissociation rate from human platelet GPIIb/IIIa receptors that might allow for once-a-day p.o. dosage.

Antibacterials. synthesis and structure-activity studies of 3-aryl-2-oxooxazolidines. 4. Multiply-substituted aryl derivatives

The synthesis and structure-activity relationship (SAR) studies of the effect of different polysubstitution patterns in the aromatic ring of 5-(acetamidomethyl)oxazolidinone antibacterials (I) on antibacterial activity are presented. Compounds I were prepared by the six-step synthesis described previously (Gregory, W. A.; et al. J. Med. Chem. [formula: see text] 1989, 32, 1673), electrophilic aromatic substitution reactions of 3-substituted compounds, and functional-group interchange reactions of 3,4-disubstituted compounds. Antibacterial evaluation of compounds I against Staphylococcus aureus and Enterococcus faecalis gave the following results. The 2,4- and 2,5-disubstituted derivatives have weak or no antibacterial activity. Antibacterial activities of 3,4-disubstituted compounds are comparable to those of the 4-monosubstituted analogues for small 3-substituents (smaller than Br), but decline rapidly for larger 3-substituents. 3,4-Annulated derivatives are comparable in activity to their open-chain analogues. 3,5-Disubstituted and 3,4,5- and 2,4,6-trisubstituted derivatives are devoid of antibacterial activity.

Antibacterials. Synthesis and structure-activity studies of 3-aryl-2-oxooxazolidines. 1. The "B" group

The synthesis and structure/activity studies of the effect of varying the "B" group in a series of oxazolidinone antibacterials (I) are described. Two synthetic routes were used: (1) alkylation of aniline with glycidol followed by dialkyl carbonate heterocyclization to afford I (A = H, B = OH), whose arene ring was further elaborated by using electrophilic aromatic substitution methodology; (2) cycloaddition of substituted aryl isocyanates with epoxides to give A and B with a variety of values. I with B = OH or Br were converted to other "B" functionalities by using SN2 methodology. Antibacterial evaluation of compounds I with A = acetyl, isopropyl, methylthio, methylsulfinyl, methylsulfonyl, and sulfonamido and a variety of different "B" groups against Staphylococcus aureus and Enterococcus faecalis concluded that the compounds with B = aminoacyl, and particularly acetamido, were the most active of those examined in each A series, possessing MICs in the range of 0.5-4 micrograms/mL for the most active compounds described.

The in vitro dental plaque inhibitory properties of a series of N-[1-alkyl-4(1H)-pyridinylidene]alkylamines

A series of novel N-[1-alkyl-4(1H)-pyridinylidene]alkylamine hydrohalides has been prepared and evaluated as inhibitors of dental plaque formation, in vitro. Several members of the series exhibited potency ca. 9-fold greater than that of chlorhexidine vs Streptococcus sobrinus 6715-13. The di-n-octyl analogue, 11 (pirtenidine), was found to be highly efficacious against several other oral plaque-forming microorganisms and is presently undergoing preclinical evaluation.

Mechanism of action of DuP 721: inhibition of an early event during initiation of protein synthesis

The mode of action of DuP 721 was investigated. This compound was active primarily against gram-positive bacteria, including multiply resistant strains of staphylococci. Although inactive against wild-type Escherichia coli, DuP 721 did inhibit E. coli when the outer membrane was perturbed by genetic or chemical means. Pulse-labeling studies with E. coli PLB-3252, a membrane-defective strain, showed that DuP 721 inhibited amino acid incorporation into proteins. The 50% inhibitory concentration of DuP 721 for protein synthesis was 3.8 micrograms/ml, but it was greater than 64 micrograms/ml for RNA and DNA syntheses. The direct addition of DuP 721 to cell-free systems did not inhibit any of the reactions of protein synthesis from chain initiation through chain elongation with either synthetic or natural mRNA as template. However, cell extracts prepared from DuP 721 growth-arrested cells were defective in initiation-dependent polypeptide synthesis directed by MS2 bacteriophage RNA. These cell-free extracts were not defective in polypeptide elongation or in fMet-tRNA(fMet)-dependent polypeptide synthesis stimulated by poly(G.U). We conclude, therefore, that DuP 721 exerts its primary action at a step preceding the interaction of fMet-tRNA(fMet) and 30S ribosomal subunits with the initiator codon.

The mechanism of action of DuP 721, a new antibacterial agent: effects on macromolecular synthesis

Pulse labeling studies with Bacillus subtilis showed that DuP 721 inhibited protein synthesis. The IC50 of DuP 721 for protein synthesis was 0.25 micrograms/ml but it was greater than 32 micrograms/ml for RNA and DNA synthesis. In cell-free systems, DuP 721 concentrations up to 100 microM did not inhibit peptide chain elongation reactions under conditions where chloramphenicol, tetracycline and hygromycin B inhibited these reactions. Furthermore, Dup 721 did not cause phenotypic suppression of nonsense mutations suggesting that DuP 721 did not inhibit peptide chain termination. Thus, the mechanism of action of DuP 721 is at a target preceeding chain elongation.

Oxazolidinones, a new class of synthetic antibacterial agents: in vitro and in vivo activities of DuP 105 and DuP 721

DuP 721 (p-acetylphenyloxooxazolidinylmethylacetamide) and DuP 105 (a methylsulfinyl derivative) are orally active representatives of the oxazolidinones, a new class of synthetic antibacterial agents. Their antibacterial spectrum includes staphylococci, streptococci, and Bacteroides fragilis strains. The compounds have equal activity against staphylococcal strains susceptible or resistant to beta-lactam antibiotics, including methicillin-resistant strains. The MICs for 90% of the strains (MIC90s) against staphylococcal isolates were 1 to 4 micrograms/ml for DuP 721 and 4 to 16 micrograms/ml for DuP 105, compared with 1 to 2 micrograms/ml for vancomycin, 0.5 microgram/ml for ciprofloxacin, and 2 to greater than 16 micrograms/ml for imipenem. The MIC90s against group D streptococci were 4 micrograms/ml for DuP 721, 16 micrograms/ml for DuP 105, and 2 micrograms/ml for vancomycin, ciprofloxacin, and imipenem. MIC90s against B. fragilis isolates were 4 micrograms/ml for DuP 721, 16 micrograms/ml for DuP 105, and 8 micrograms/ml for cefoxitin. DuP 721 and DuP 105 administered by either the oral or the parenteral route were protective against staphylococcal and streptococcal infections in mice. The 50% effective doses were 2 to 10 mg/kg for DuP 721, 9 to 23 mg/kg for DuP 105, and 2 to 12 mg/kg for vancomycin. These results indicate that further studies of compounds of the oxazolidinone series are warranted.

Bispyridinamines: a new class of topical antimicrobial agents as inhibitors of dental plaque

A series of N,N'-polyalkylenebis[4-(substituted-amino)pyridines] has been prepared, and members have been evaluated as potential anti-dental plaque agents. From among the most active members of the series, one compound, N,N'-[1,10-decanediyldi-1(4H)-pyridinyl-4-ylidene]bis(1-octanam ine) dihydrochloride, octenidine, was selected as a candidate for clinical study.

Relationship between structure and antiplaque and antimicrobial activities for a series of bispyridines

A series of bispyridines were examined for their bactericidal activities against in vitro, preformed, pure-culture plaques of selected oral plaque-forming bacteria. The antimicrobial activities of these agents were examined in relation to their molecular configurations. These studies demonstrated that the length of the interpyridine polymethylene group bridge and the length of the alkyl side chain were important determinants of antiplaque and antimicrobial efficacy. The most potent compounds of the bispyridine series were studied to determine the minimal conditions (concentration, duration, and frequency) of treatment required for likely clinical efficacy.

In vitro antiplaque activity of octenidine dihydrochloride (WIN 41464-2) against preformed plaques of selected oral plaque-forming microorganisms

The antibacterial activity of octenidine dihydrochloride (WIN 41464-2) against intact preformed in vitro plaques of four indigenous oral plaque-forming microorganisms, Streptococcus mutans, Streptococcus sanguis, Actinomyces viscosus, and Actinomyces naeslundii, was studied. Both absolute (plaque bactericidal index) and relative (chlorhexidine coefficient) indices of antiplaque efficacy were established. Octenidine dihydrochloride compared favorably with chlorhexidine digluconate with respect to overall antiplaque potency in this in vitro plaque bactericidal model. These data indicate that prudent selection of treatment concentration and duration and frequency of exposure should provide an effective means to aid in controlling dental caries and Actinomyces-associated disease in vivo.

The repressible metabolism of sorbitol (D-glucitol) by intact cells of the oral plaque-forming bacterium Streptococcus mutans

Sorbitol metabolism of Streptococcus mutans was studied. Cocci adapted to growth in sorbitol, glucose or both were challenged to grow on and to ferment those carbohydrates in pH-controlled defined media with intact cells capable of metabolic inductions and regulations. Glucose degradation when in high concentration did not depend upon induction of glucose-specific phosphoenolpyruvate-dependent phosphotransferase activity, as it did at low glucose concentrations. Sorbitol utilization was signalled by the induction of sorbitol-specific phosphoenolpyruvate-dependent phosphotransferase and sorbitol-6-phosphate dehydrogenase activities which persisted throughout the growth cycle. However, when even low levels of glucose were present, sorbitol transport and catabolic activities were rapidly repressed and they were not de-repressed until essentially all glucose had been utilized. Metabolism of sorbitol thus relies on the sorbitol phosphotransferase/sorbitol-6-phosphate dehydrogenase pathway whose activity is sensitively repressed in the presence of glucose.

Sucrose transport by Streptococcus mutans. Evidence for multiple transport systems

The transport of sucrose by selected mutant and wild-type cells of Streptococcus mutans was studied using washed cocci harvested at appropriate phases of growth, incubated in the presence of fluoride and appropriately labelled substrates. The rapid sucrose uptake observed cannot be ascribed to possible extracellular formation of hexoses from sucrose and their subsequent transport, formation of intracellular glycogen-like polysaccharide, or binding of sucrose or extracellular glucans to the cocci. Rather, there are at least three discrete transport systems for sucrose, two of which are phosphoenolpyruvate-dependent phosphotransferases with relatively low apparent Km values and the other a non-phosphotransferase (non-PTS) third transport system (termed TTS) with a relatively high apparent Km. For strain 6715-13 mutant 33, the Km values are 6.25 X 10(-5) M, 2.4 X 10(-4) M, and 3.0 X 10(-3) M, respectively: strain NCTC-10449, the Km values are 7.1 X 10(-5) M, 2.5 X 10(-4) M and 3.3 X 10(-3) M, respectively. The two lower Km systems could not be demonstrated in mid-log phase glucose-adapted cocci, a condition known to repress sucrose-specific phosphotransferase activity, but under these conditions the highest Km system persists. Also, a mutant devoid of sucrose-specific phosphotransferase activity fails to evidence the two high affinity (low apparent Km) systems, but still has the lowest affinity (highest Km) system. There was essentially no uptake at 4 degrees C indicating these processes are energy dependent. The third transport system, whose nature is unknown, appears to function under conditions of sucrose abundance and rapid growth which are known to repress phosphoenolpyruvate-dependent sucrose-specific phosphotransferase activity in S. mutans. These multiple transport systems seem well-adapted to S. mutans which is faced with fluctuating supplies of sucrose in its natural habitat on the surfaces of teeth.

Predominant microflora associated with human dental periapical abscesses

The microflora of periapical abscesses of teeth free of periodontal disease was studied. Permucosal aspiration of abscess contents and anaerobic cultural, microscopic, and biochemical techniques indicated a mixed but somewhat specific and relatively limited facultative and obligate anaerobic flora with Fusobacterium nucleatum and Streptococcus mitis as a frequent pair.

Effect of growth conditions on sucrose phosphotransferase activity of Streptococcus mutans

Sucrose and glucose phosphoenolpyruvate-dependent phosphotransferase (PTS) activities were studied in growing cultures of Streptococcus mutans serotype c and d/g cells adapted to either glucose or sucrose. Both acid production and optical absorbance were used to monitor growth in pH-controlled defined growth medium. The sucrose PTS activity appeared to be significant only under conditions of substrate limitation or slow growth as a result of low environmental pH. However, under environmental conditions which permitted rapid growth sucrose PTS activity appeared to be repressed, and only when the cells approached substrate-limited stationary phase after growth on high sucrose-supplemented medium was significant sucrose PTS activity again observed. A mutant apparently defective in sucrose PTS activity grew rapidly and produced acid under conditions of high environmental sucrose level but showed no sucrose PTS activity when the culture approached stationary phase. The mutant, however, after adaptation to glucose, demonstrated significant glucose PTS once the culture had attained the stationary growth phase. During diauxie growth in the presence of glucose and sucrose, there were sequential apparent inductions and repressions of glucose and sucrose PTS activities corresponding to decreases and increases of growth rate on the two substrates. Thus, S. mutans possesses at least two transport mechanisms for each substrate studied. One system (PTS) functions under conditions permitting slow growth and another functions under conditions permitting rapid growth.

Phosphoenolpyruvate-dependent sucrose phosphotransferase activity in five serotypes of Streptococcus mutans

An inducible phosphoenolpyruvate-dependent sucrose phosphotransferase system has been demonstrated in decryptified cell suspensions of the various common serotypes of the cariogenic microorganism Streptococcus mutans.

Phosphoenolpyruvate-dependent sucrose phosphotransferase activity in Streptococcus mutans NCTC 10449

A phosphoenolpyruvate-dependent sucrose phosphotransferase system (PTS) has been demonstrated, by an enzyme-coupled reaction and product isolation, in decryptified cell suspensions of the cariogenic microorganism Streptococcus mutans NCTC 10449. The apparent sucrose PTS reaction for sucrose-adapted, sucrose-challenged cells displayed saturation kinetics with an apparent Km of 7.14 x 10(-5) M, which was distinct from the Km of the glucose PTS activity of glucose-adapted, glucose-challenged cells. Both the sucrose and the glucose PTS activities appear to be inducible and under separate genetic control. The sucrose PTS reaction demonstrated in decryptified cells had an absolute requirement for phosphoenolpyruvate. Only 2-phosphoglycerate, the immediate glycolytic precursor of phosphoenolpyruvate, was found to substitute for phosphoenolpyruvate in this reaction in the absence of fluoride. The sucrose PTS activity of sucrose-adapted cells was competitively inhibited by raffinose and lactose; these same sugars had no effect on the apparent glucose PTS activity. Fructose was the only carbohydrate tested other than sucrose which elicited an apparent PTS reaction in sucrose-adapted cells. The product of the sucrose PTS reaction was isolated and behaved chromatographically on a Dowex-1-X8 column like a monophosphate ester. Alkaline phosphatase treatment of the presumptive sucrose monophosphate liberated a component which behaved chromatographically like free sucrose. Subsequent acid hydrolysis of this component produced moieties which behaved chromatographically like glucose and fructose.

In vitro evaluation of seven cationic detergents as antiplaque agents

The bactericidal efficacy of seven cationic detergents was studied in vitro against intact performed plaques of representative strains of four oral dental plaque-forming microorganisms: Streptococcus mutans, Streptococcus sanguis, Actinomyces viscosus, and Actinomyces naeslundii. Both absolute (plaque bactericidal index) and relative (chlorhexidine coefficient) indexes of antiplaque activity were established. Only cetyltrimethylammonium bromide was more efficacious than the reference agent, the bisbiguanide chlorhexidine, for the apparently more potent tooth-adherent cariogenic and periodontopathic elements, respectively, of the in vivo plaque microflora, S. mutans and A. viscosus.

Selective medium for isolation of Eikenella corrodens from periodontal lesions

The addition of 5 microgram of clindamycin per ml to a modified Todd-Hewitt growth medium permitted the ready enumeration of Eikenella corrodens from deep periodontal lesions because it allowed differential growth amongst the periodontal pocket gram-negative microaerophilic-anaerobic flora, maximized the numbers of E. corrodens in such culture, and inhibited the growth of most of the other confounding microorganisms.

Activity of three 8-hydroxyquinoline derivatives against in vitro dental plaque

Three 8-hydroxyquinoline derivatives, assessed using an in vitro preformed dental plaque model system, were differentially inhibitory for four plaque-forming microorganisms.

Structural requirements of guanide, biguanide, and bisbiguanide agents for antiplaque activity

The bactericidal efficacy of 16 guanide, biguanide, and bisbiguanide agents was studied in vitro against intact preformed plaques of four oral (plaque-forming) microorganisms: Streptococcus mutans, S. sanguis, Actinomyces viscosus, and A. naeslundii. The activities of these agents were examined in relation to their molecular configurations. These studies indicated that the bis- and biguanide configurations are important for efficacy, as is the length of the alkyl side chain. No structural moiety determined efficacy by itself. Furthermore, the activities of these agents were studied to determine the minimal conditions (concentration, duration, and frequency) of treatment required for likely clinical efficacy. At least six agents were judged to have equal or greater efficacy than the reference agent, chlorhexidine digluconate. A plaque bactericidal index was derived for the most potent agents, and comparison to the bactericidal properties of chlorhexidine was expressed as a chlorhexidine coefficient.

In vitro evaluation of three iodine-containing compounds as antiplaque agents

The antibacterial activity of three iodine-containing compounds was determined for strains of four dental plaque-forming microorganisms, using an in vitro preclinical plaque model system. Solutions of inorganic iodine, povidone-iodine, and Wescodyne were tested for antiplaque activity against preformed plaques of a number of strains of Streptococcus mutans, Streptococcus sanguis, Actinomyces viscosus, and Actinomyces naeslundii. Solutions of inorganic iodine were more effective as antiplaque agents, with respect to minimal bactericidal concentration and time and frequency of treatments, than solutions of Wescodyne and povidone-iodine. Inorganic iodine appeared to be particularly effective against the most cariogenic (S. mutans) and periodontopathic (A. viscosus) organisms while allowing survival of the least orally pathogenic plaque-forming microorganism (S. sanguis). It is suggested that topical application of solutions of inorganic iodine may be useful in controlling dental caries and actinomyces-associated periodontal disease.