Plaque Formers Research Articles

The influence of saliva on the hydrophobic surface properties of bacteria isolated from oral sites of macaque monkeys

The surface hydrophobicity of 64 bacterial strains isolated from discrete, intra-oral sites of monkeys (Macaca fascicularis) was determined by measuring their affinity for hexadecane. Bacteria were also exposed to monkey saliva which either increased or reduced the surface hydrophobicity of the cells. After exposure to saliva those bacteria isolated solely from the mucosal surfaces were significantly more hydrophobic than bacteria (Streptococcus mutans and Actinomyces spp.) whose major habitat was the dentition. Streptococcus sanguis strains isolated from all intra-oral sites and among the early plaque formers were as hydrophobic as the organisms isolated only from the mucosal surfaces.

The influence of saliva on the hydrophobic surface properties of bacteria isolated from oral sites of macaque monkeys

The surface hydrophobicity of 64 bacterial strains isolated from discrete, intra-oral sites of monkeys (Macaca fascicularis) was determined by measuring their affinity for hexadecane. Bacteria were also exposed to monkey saliva which either increased or reduced the surface hydrophobicity of the cells. After exposure to saliva those bacteria isolated solely from the mucosal surfaces were significantly more hydrophobic than bacteria (Streptococcus mutans and Actinomyces spp.) whose major habitat was the dentition. Streptococcus sanguis strains isolated from all intra-oral sites and among the early plaque formers were as hydrophobic as the organisms isolated only from the mucosal surfaces.

Damaged-site independent mutagenesis of phage λ produced by inducible error-prone repair

The existence of damaged-site independent mutagenesis is confirmed here by scoring the appearance of clear-plaque (c-) or virulent (vir) forward mutations on intact (non-irradiated) phage lambda grown on UV-irradiated E. coli K12 hosts. The mutation frequency was measured as a function of the incubation time between the occurrence of host DNA lesions and phage infection. The time course of mutagenesis of intact phage followed the induction pattern observed upon UV-reactivation of UV-damaged phage by Defais et al. (1976). Intact phage did not mutate in UV-irradiated hosts carrying the uvm-25 mutation known to prevent the occurrence of UV-reactivation. These findings suggest that damaged-site independent mutagenesis results from inducible error-prone repair. Clear-plaque mutations arising on intact phage were mostly found in phage bursts consisting of clear and turbid plaque formers whereas UV-damaged phage gave rise to mostly clear-plaque formers. Contrarily to damaged-site dependent mutagenesis, damaged-site independent mutagenesis can arise even at late times during the phage replication cycle. Our data indicate that about half of the phage mutations that arise upon UV-reactivation are damaged-site independent mutations. Replication of intact phage DNA in a host during induction of SOS functions provides a sensitive assay for the detection of damaged-site independent mutagenesis.

Bacteriophage lambda containing two temperature-sensitive mutations in the cl gene produces clear plaque at 30°

When λ cIts2 Psus3 was crossed with λ Nsus7 sus53 cI857, clear plaque formers at 30° were obtained among the λ N +P + recombinants. This clear recombinant of λ was shown to contain the two cI ts mutations, 2 and 857, of the parents. It was also observed that crosses between any two λ cI ts mutants, from a list of eight, produced recombinants forming clear plaques at 30°. These suggest that no pair of ts mutations of the eight tested are compatible with the functioning of the repressor even at 30° when they are present in cis.

A cointegrate of the bacteriophage P1 genome and the conjugative R plasmid R100

Restriction cleavage analysis identified a P1CmSmSuTc plasmid isolated by Mise and Arber (1976) ( Virology 69, 191–205) as a cointegrate between bacteriophage P1 and the R plasmid R100. Cointegration occurred by reciprocal recombination between the IS1 element of P1 and IS1b of R100. It involved neither gain nor loss of genetic material, so that the cointegrate carries three IS1 elements in the same orientation. The cointegrate propagates with relatively high stability as plasmid in Escherichia coli host bacteria. It displays the Tra + functions of R100, incompatibility FII of R100, and incompatibility Y of P1, Res + (P1), Mod + (P1) functions of P1 and P1 immunity. Production of P1 phage particles is inducible as for wild type P1. However, because of the large genome size of 180 kb, progeny phage particles contain only a fraction (about 100 kb) of the cointegrate genome. Because of cyclic permutation all genome regions are equally represented in a population of the phage particles of an induced lysate. Occasionally, reciprocal recombination between IS1 elements allows the restoration of the P1 genome. These segregants are found as plaque formers at a rate of about 1 per 300 phage particles in induced lysates.

Mutagenesis of ultraviolet-irradiated lambda phage by host cell irradiation: induction of Weigle mutagenesis is not an all-or-none process.

Ultraviolet mutagenesis of lambda phage to clear plaque formers is the same in the total phage population and in subpopulations of phage which have also mutated to gam- or at an amber codon. This is true for phage assayed in host cells in which Weigle mutagenesis has been either partially induced by low levels of ultraviolet irradiation, or fully induced by higher levels. If induction of Weigle mutagenesis were all-or-none, clear plaque formers in phage subpopulations selected for another mutation elsewhere would come mainly from induced cells; then the clear plaque mutation rate would always be that for fully induced host cells. Therefore, induction requires more than one lesion in host cell DNA. Although thymine starvation of cells induces synthesis of recA protein, it does not induce Weigle mutagenesis; in fact starvation inhibits induction of this process on subsequent ultraviolet irradiation of the cells.

The lymphoproliferative response during human experimental gingivitis

The lymphocyte blastogenic responses to antigen preparations of bacteria from dental microbial plaque and to other non‐oral stimulants were longitudinally assayed in eitht adult subjects using the experimental gingivitis model. During the 28 days of the experimental period, these subjects abstained from all oral hygiene procedures which let to accumulatio of increased amounts of microbial dental plaque and subsequent gingivitis. In general, all subjects demonstrated a significant increase in the lymphoproliferative response to all doses of phytohemagglutinin (PHA) during the experimental period. The subjects were divided into 2 groups based on rate of plaque accumulation. Slow plaque formers exhibited a gradual linear increase in blastogenic response to bacterial antigen preparations throughout the experimental period. In the group characterixed by rapid accumulation of plaque, a marked early increase in blastogenic responses to antigens of Actinomyces viscosus, Actinomyces naeslundii, Bacteroides melaninogenicus, and Treponema denticola was observed. These same subjects, however, demonstrated a reduction in lymphocyte response to the above antigens during the later phase of the experimental period, when gingivitis was most severe. This decrease, in light of the similtaneous increase in PHA response, suggests the existence of a homeostatic mechanism to control the immune response during episodes of increased antigen load.

Effect of some polyvalent cations on plaque formation in vivo

The purpose of the present study was to investigate the effect of polyvalent cations on plaque formation in a test panel of students. Heavy plaque formers were selected and plaque formation was enhanced by frequent sucrose rinses. Mouthrinses were performed twice daily with 20 mmol/l SnF2, SnCl2, AlCl3, ZnCl2 and MgCl2, and 40 mmol/l NaF and NaCl. It was found that SnF2 AND SnCl2 exhibited a marked plaque-inhibiting capacity compared with NaF or NaCl. The aluminum, zinc and magnesium salts also reduced plaque formation, although not to the same degree. Polyvalent cations may prevent plque formattion by interaction with negatively charged plaque components essential in the adsorption mechanism, or by inhibiting some enzyme activity essential in plaque formation.

Mutagenesis of lambda phage: 5-bromouracil and hydroxylamine

Mutagenesis by 5-bromouracil of lambda phage to clear plaque formers does not depend on the recA function of the host E. coli cell or on the red function of the phage. Pretreatment of the host cells with ultraviolet light does not affect bromouracil mutagenesis of the adsorbed phage. Mutagenesis by hydroxlamine to clear plaque formers takes place at a high level in recA- host cells, and is not changed by preirradiation of of rec+ (wild type) hosts with ultraviolet light. Thus, bromouracil and hydroxylamine appear to mutate lambda phage by a process which differs from that responsible for ultraviolet mutagenesis. Two characteristics of bromouracil mutagenesis--the nonlinear dependence of the number of mutants on bromouracil incorporation, and a high frequency of heterozygotes--fit in with Rydberg's (1977) picture of bromouracil mutagenesis as a consequence of base mispairing, with mismatch repair removing the mutations at low incorporation of the analog.

Initial colonization of teeth in monkeys as related to diet.

The initial phases of plaque development on nonretentive tooth surfaces were studied bacteriologically in Macaca irus monkeys fed by stomach tube and provided with various oral supplements. Except for the oral implantation of Streptococcus mutans in some of the animals, the oral flora was not changed prior to the studies. Dental plaque was allowed to develop on initially cleaned tooth surfaces for 3 to 5 h. Plaque samples were collected and cultured on a number of selective and nonselective agar media, and several hundred isolates from each sample were isolated and identified. The numerically predominant organisms in initial plaque were S. mutans, Streptococcus sanguis, and Actinomyces viscosus. Additional organisms regularly found, but usually in smaller numbers, were Streptococcus mitior and a group of fastidious gram-negative rods including Haemophilus species, Eikenella corrodens, and Actinobacillus actinomycetem-comitans. The colonization of S. mutans was dependent on sucrose and occurred at the expense of S. sanguis. In these experiments S. mutans accounted for 25 to 65% of the primary plaque formers. All other species encountered colonized the teeth irrespective of the diet. It is postulated that the early sucrose-dependent establishment of S. mutans directly on the enamel pellicle plays a key role in the development of a cariogenic plaque.

Recombinants between P22 and P1Cm

Two types of high frequency transducing (HFT) phage lysates for the chloramphenicol (Cm) resistance gene were obtained from P22 phage grown on P1Cm-lysogenic Salmonella typhimurium by a stepwise enrichment procedure. The transduction frequency of the Cm marker by the first type of phage was m.o.i.-dependent, and P22 phage was necessary as a helper phage for transduction. On the other hand, the second type of phage could transduce the Cm marker at high frequencies even in the absence of helper phages. It was shown that the first type of phage could not reproduce progeny phages by itself, while the second could, and contained all the phage genes essential for growth as well as for Cm resistance. Both phages had characteristics very similar to those of P22, not of P1, and were designated P22dCm (“d” for defective) and P22Cm, respectively. Some of P22Cm-lysogenic bacteria produced large numbers of plaque formers when merely incubated in enriched broth. The ability to form colonies of P22Cm-lysogenic bacteria was considerably decreased compared to P22-lysogenic bacteria. The transduction frequency of the pro marker by phage P22Cm spontaneously released by P22Cm-lysogenic bacteria was much lower than that of a uv-induced P22 phage lysate.

Cro mutants of phage 434

Phage 434 cro 434 mutants have been isolated and characterized as plaque formers on groN bacteria, which block wild-type 434 and λ development at the level of action of the N gene product (Georgopoulos, 1971). Like the corresponding λ cro λ mutants, they map within the immunity region and to the right of the cI gene, they overproduce the exonuclease gene product, they are unable to propagate on wild-type bacteria (especially at 42°), and in mixed infections they suppress the growth of heteroimmune but not homoimmune cro + phage.

Chemotactic ability of dental plaque upon autologous or heterologous human polymorphonuclear leukocytes.

The chemotactic effect of pooled human plaque suspension, supernatant, and ultrafiltrate upon heterologous human PMNs was investigated using the Boyden chamber technique. It was observed that pooled plaque suspensions (20 mg/ml) were consistently chemotactic for heterologous human PMN cells. Whole plaque suspensions were most chemotactic, and the supernatant was approximately half as active, while the bacteria-free ultrafiltrate induced a negligible chemotactic response. Chemotactic assays of individual plaque suspensions were also performed. Twelve male subjects were paired according to age and PDI scores to assess whether the PMN cells of certain individuals responded differently to their autologous plaque. When comparing subjects with high or low PDI scores, there were no significant differences in the chemotactic responses. However, a trend of reduced chemotaxis was observed in most subjects with a high PDI. When the subjects were arbitrarily divided into groups with high and low plaque indices, a greater overall chemotactic response was generated by the higher plaque formers. The differences between the two groups, however, were not statistically significant.

Plaque formation by mixed cultures of nonprimary plaque-forming microorganisms.

Some oral organisms that do not form artificial plaque in pure culture interacted to form adherent plaque when combined in mixed culture. The presence of a nonprimary plaque-forming strain of Streptococcus salivarius in combinations with one of several other nonprimary plaque formers, resulted in depositions of large quantities of plaque containing significant amounts of a fructose-positive polysaccharide.

In vitro genetic recombination of bacteriophage lambda.

DNA of bacteriophage lambda recombines in a cell-free extract prepared from an induced Escherichia coli lysogen of bacteriophage lambda. The assay for recombination in vitro takes advantage of the ability of such an extract to package lambda DNA and to assemble complete phage particles. For example, when lambda DNA that has been extracted from phage with the immunity of 434 is added to an extract, infectious lambda imm 434 particles are produced. The precursor DNA molecule in this packaging reaction is a multichromosomal polymer; circular monomers, for example, are not packaged.Nevertheless, when 434 circular DNA monomers are added to an extract, some phage that contain the imm 434 marker are produced. In this case, the circular DNA had recombined with lambda DNA in the extract and thereby had become part of a polymeric structure, which by the normal packaging process could give rise to infectious particles with the imm 434 marker. Genetic recombination is demonstrated when imm 434 circular monomer DNA carries amber mutations in genes A and B; then most of the 434 plaque formers produced in vitro are A(+)B(+), the genotype of the endogenous lambda DNA. Genetic crossing-over occurs through a region that contains the prophage attachment site, suggesting that recombination is carried out by the lambda Int functions. The 434 recombinant plaque formers are particles physically identical to wild-type 434 particles, as judged by their buoyant density in a CsCl equilibrium gradient.

Dose effect of immune ribonucleic acid fraction on antibody formation.

ABSTRACTAn immune ribonucleic acid (iRNA) preparation was extracted with phenol from the spleens of mice immunized with sheep red blood cells (SRBC). When mice were injected intravenously with iRNA, rosette formers in the spleens of such mice were demonstrated but plaque formers and serum antibody could not be detected. As reported previously, iRNA against SRBC also could induce memory cells capable of responding to a small amount of antigen to produce a high titer of antibody. The necessary interval between the iRNA and antigen stimulation for induction of a secondary response was found to be three weeks or more. Presence of an optimal dose of iRNA for the induction of memory cells was demonstrated, and the role of iRNA in antibody formation and the optimal dose of iRNA for the induction of memory cells were discussed.

Phenotypic mixing of envelope proteins of the parainfluenza virus SV5 and vesicular stomatitis virus.

Cells mixedly infected with parainfluenza virus SV5 and vesicular stomatitis virus (VSV) yield phenotypically mixed virions, in addition to both parental types. Two types of phenotypically mixed virions have been identified: 0.6 to 1.2% of the VSV plaque formers were neutralized by SV5 antiserum, but not by VSV antiserum, suggesting the presence of a VSV genome in an SV5 envelope; 9 to 45% of the VSV plaque formers were neutralized by both antisera, indicating the presence of both SV5 and VSV antigens in their envelopes. The presence of SV5 antigen in virions with the typical bullet-shaped appearance of VSV was confirmed with ferritin-labeled anti-SV5 antibody. In contrast to standard VSV, phenotypically mixed virions adsorbed to and eluted from chicken erythrocytes, indicating that these virions contained in their envelopes SV5 hemagglutinin, and possibly neuraminidase. Thus, the VSV nucleocapsid can interact with membranes which contain SV5 proteins in the manner which leads to virus maturation, and the production of a high yield of phenotypically mixed virions with the morphology of VSV indicates that this process can function efficiently. No evidence of genetic recombination between the two viruses was found. These results raise the possibility of an evolutionary relatedness between the paramyxoviruses and the rhabdoviruses.

Transformation of mouse 3T3 cells by T antigen-forming defective SV40 virions (T particles)

The T antigen-forming defective deletion mutants (T particles) of SV40 transformed mouse 3T3 cells with the same efficiency as that obtained with plaque formers. Replication of the defective viral genome appeared to occur in the heterokaryons of 3T3 cells transformed by T particles and susceptible African green monkey kidney cells.

Studies on DNA from low-density particles of SV40: I. Heterogeneous defective virions produced by successive undiluted passages

Successive undiluted passages of SV40 (small plaque) in African green monkey kidney cells result in the production of heterogeneous defective particles of lower densities than that of infectious virions. Band centrifugation in neutral and alkaline solutions and electron microscopy have been used to study DNA preparations from light virions fractionated by cesium chloride density gradient centrifugation. The studies have demonstrated that light virions contain circular DNA molecules smaller than those from plaque formers. Shortening of DNA would account for defectiveness as well as alteration in density of virions.

STUDIES ON CHARACTERISTICS OF PLAQUE MUTANTS OF ECHO 6' VIRUS

ECHO 6′ virus produces plaques of 1-2 mm in diameter on MS cell monolayer. The large plaque mutants of 6-10 mm were obtained from the virus passaged in the presence of anti-ECHO 6 serum. This paper compares the various characteristics of the mutants and the small plaque formers including the original ECHO 6′ virus strain.The large plaque mutants were more sensitive to anti-ECHO 6 and 6′ sera than small plaque formers. The mutants began to grow earlier and produced more virus particles than small plaque formers.The effects of certain drugs on plaque formation were examined. MgCl2 and cysteine had no effects except on certain strains. Dextran sulfate promoted the plaque formation in all the strains. A low concentration of sodium bicarbonate promoted the plaque f of mation only in the small plaque formers.The original strain and one small plaque former had the ability of hemagglutination, but one small plaque former and all mutants did not.Comparing the above characteeristics, it is ascertained that the plaque mutation linked to antigenic character but not necessarily to the other characterisitics.