Characterization of an inducible bacteriophage from a leukotoxic strain of Actinobacillus actinomycetemcomitans

Bacteriophages: the dawn of a new era in periodontal microbiology?

The oral microbiome, populated by a diverse range of species, plays a critical role in the initiation and progression of periodontal disease. The most dominant yet little-discussed players in the microbiome, the bacteriophages, influence the health and disease of the host in various ways. They, not only contribute to periodontal health by preventing the colonization of pathogens and disrupting biofilms but also play a role in periodontal disease by upregulating the virulence of periodontal pathogens through the transfer of antibiotic resistance and virulence factors. Since bacteriophages selectively infect only bacterial cells, they have an enormous scope to be used as a therapeutic strategy; recently, phage therapy has been successfully used to treat antibiotic-resistant systemic infections. Their ability to disrupt biofilms widens the scope against periodontal pathogens and dental plaque biofilms in periodontitis. Future research focussing on the oral phageome and phage therapy's effectiveness and safety could pave way for new avenues in periodontal therapy. This review explores our current understanding of bacteriophages, their interactions in the oral microbiome, and their therapeutic potential in periodontal disease.

An Inducible Microbacterium Prophage vB_MoxS-R1 Represents a Novel Lineage of Siphovirus

Lytic and lysogenic infections are the main strategies used by viruses to interact with microbial hosts. The genetic information of prophages provides insights into the nature of phages and their potential influences on hosts. Here, the siphovirus vB_MoxS-R1 was induced from a Microbacterium strain isolated from an estuarine Synechococcus culture. vB_MoxS-R1 has a high replication capability, with an estimated burst size of 2000 virions per cell. vB_MoxS-R1 represents a novel phage genus-based genomic analysis. Six transcriptional regulator (TR) genes were predicted in the vB_MoxS-R1 genome. Four of these TR genes are involved in stress responses, virulence and amino acid transportation in bacteria, suggesting that they may play roles in regulating the host cell metabolism in response to external environmental changes. A glycerophosphodiester phosphodiesterase gene related to phosphorus acquisition was also identified in the vB_MoxS-R1 genome. The presence of six TR genes and the phosphorus-acquisition gene suggests that prophage vB_MoxS-R1 has the potential to influence survival and adaptation of its host during lysogeny. Possession of four endonuclease genes in the prophage genome suggests that vB_MoxS-R1 is likely involved in DNA recombination or gene conversion and further influences host evolution.

The human oral virome: Shedding light on the dark matter

Mediators of the initiation, development, and recurrence of periodontitis include the oral microbiome embedded in subgingival plaque and the host immune response to a dysbiosis within this dynamic and complex microbial community. Although mediators have been studied extensively, researchers in the field have been unable to fully ascribe certain clinical presentations of periodontitis to their nature. Emergence of high-throughput sequencing technologies has resulted in better characterization of the microbial oral dysbiosis that extends beyond the extensively studied putative bacterial periodontopathogens to a shift in the oral virome composition during disease conditions. Although the biological dark matter inserted by retroviruses was once believed to be nonfunctional, research has revealed that it encodes historical viral-eukaryotic interactions and influences host development. The objective of this review is to evaluate the proposed association of herpesviruses to the etiology and pathogenesis of periodontal disease and survey the highly abundant prokaryotic viruses to delineate their potential roles in biofilm dynamics, as well as their interactions with putative bacterial periodontopathogens and eukaryotic cells. The findings suggest that potential novel periodontal therapies targeting or utilizing the oral virome can alleviate certain clinical presentations of periodontitis. Perhaps it is time to embrace the viral dark matter within the periodontal environment to fully comprehend the pathogenesis and systemic implications of periodontitis.

Diversity patterns of bacteriophages infecting Aggregatibacter and Haemophilus species across clades and niches

Aggregatibacter and Haemophilus species are relevant human commensals and opportunistic pathogens. Consequently, their bacteriophages may have significant impact on human microbial ecology and pathologies. Our aim was to reveal the prevalence and diversity of bacteriophages infecting Aggregatibacter and Haemophilus species that colonize the human body. Genome mining with comparative genomics, screening of clinical isolates, and profiling of metagenomes allowed characterization of 346 phages grouped in 52 clusters and 18 superclusters. Less than 10% of the identified phage clusters were represented by previously characterized phages. Prophage diversity patterns varied significantly for different phage types, host clades, and environmental niches. A more diverse phage community lysogenizes Haemophilus influenzae and Haemophilus parainfluenzae strains than Aggregatibacter actinomycetemcomitans and “Haemophilus ducreyi”. Co-infections occurred more often in “H. ducreyi”. Phages from Aggregatibacter actinomycetemcomitans preferably lysogenized strains of specific serotype. Prophage patterns shared by subspecies clades of different bacterial species suggest similar ecoevolutionary drivers. Changes in frequencies of DNA uptake signal sequences and guanine–cytosine content reflect phage-host long-term coevolution. Aggregatibacter and Haemophilus phages were prevalent at multiple oral sites. Together, these findings should help exploring the ecoevolutionary forces shaping virus-host interactions in the human microbiome. Putative lytic phages, especially phiKZ-like, may provide new therapeutic options.

The use of bacteriophages to biocontrol oral biofilms

Infections induced by oral biofilms include caries, as well as periodontal, and peri-implant disease, and may influence quality of life, systemic health, and expenditure. As bacterial biofilms are highly resistant and resilient to conventional antibacterial therapy, it has been difficult to combat these infections. An innovative alternative to the biocontrol of oral biofilms could be to use bacteriophages or phages, the viruses of bacteria, which are specific, non-toxic, self-proliferating, and can penetrate into biofilms. Phages for Actinomyces naeslundii, Aggregatibacter actinomycetemcomitans, Enterococcus faecalis, Fusobacterium nucleatum, Lactobacillus spp., Neisseria spp., Streptococcus spp., and Veillonella spp. have been isolated and characterised. Recombinant phage enzymes (lysins) have been shown to lyse A. naeslundii and Streptococcus spp. However, only a tiny fraction of available phages and their lysins have been explored so far. The unique properties of phages and their lysins make them promising but challenging antimicrobials. The genetics and biology of phages have to be further explored in order to determine the most effective way of applying them. Studying the effect of phages and lysins on multispecies biofilms should pave the way for microbiota engineering and microbiota-based therapy.

Genome sequence of the temperate bacteriophage PH10 from Streptococcus oralis

Exponential growing cultures of Streptococcus oralis strain OMZ 1038, isolated from human supragingival dental plaque, were found to release a bacteriophage (designated PH10) upon treatment with mitomycin C. The complete genome sequence of phage PH10 was determined. The genome was 31276 bp in size and contained 54 open reading frames. The module encoding structural proteins was highly similar to that of Streptococcus pneumoniae prophage PhiSpn_3. The most abundant phage structural protein was encoded by ORF35 and was likely processed by proteolytic cleavage. The putative endolysin from PH10, which contained a muramidase domain and a choline-binding domain, was purified and shown to have lytic activity with S. oralis, S. pneumoniae and Streptococcus mitis, but not with other streptococcal species.

Bacteriophages induced from lysogenic root canal isolates of Enterococcus faecalis

INTRODUCTION

Bacterial viruses play crucial roles in the pathogenesis of many systemic diseases. They are known to inhabit the oral cavity, both as free virions and as prophages in lysogenic bacterial strains; however, there has been no report of bacteriophages in endodontic infections. In this study, we sought to detect, isolate, and describe temperate bacteriophages harbored by Enterococcus faecalis strains isolated from endodontic infections.

METHODS

Ten E. faecalis strains were isolated from root canals of teeth undergoing retreatment following unsuccessful endodontic therapy. Mitomycin C was used to induce any prophages present in the bacterial isolates. The induced phages were purified and examined using electron microscopy. The DNA extracted from one of the phage isolates was subjected to restriction endonuclease digestion and agarose electrophoresis analysis.

RESULTS

Lysogeny was demonstrated in 4 of the 10 E. faecalis strains. Three of the lysogenic strains yielded phages exhibiting a Siphoviridae morphology, with long, non-contractile tails 130 nm in length, and spherical/icosahedral heads 41 nm in diameter. The virus induced from the fourth lysogenic E. faecalis strain had a contractile tail characteristic of Myoviridae. Restriction endonuclease analysis of NsiI and NdeI DNA fragments from one of the Siphoviridae phage isolates (phage phiEf11) indicated a genome size of approximately 41 kbp.

CONCLUSION

This is the first report of lysogenic bacteria and their inducible viruses in infected root canals.

Practical methods for determining phage growth parameters

Bacteriophage growth may be differentiated into sequential steps: (i) phage collision with an adsorption-susceptible bacterium, (ii) virion attachment, (iii) virion nucleic acid uptake, (iv) an eclipse period during which infections synthesize phage proteins and nucleic acid, (v) a "post-eclipse" period during which virions mature, (vi) a virion release step, and (vii) a diffusion-delimited period of virion extracellular search for bacteria to adsorb (1). The latent period begins at the point of virion attachment (ii) and/or nucleic acid uptake (iii) and ends with infection termination, spanning both the eclipse (iv) and the post-eclipse maturation (v) periods. For lytic phages, latent-period termination occurs at lysis, i.e., at the point of phage-progeny release (vi). A second compound step is phage adsorption, which, depending upon one's perspective, can begin with virion release (vi), may include the virion extracellular search (vii), certainly involves virion collision with (i) and then attachment to (ii) a bacterium, and ends either with irreversible virion attachment to bacteria (ii) or with phage nucleic acid uptake into cytoplasm (iii). Thus, the phage life cycle, particularly for virulent phages, consists of an adsorption period, virion attachment/nucleic acid uptake, a latent period, and virion release ((2), p. 13, citing d'Herelle). The duration of these steps together define the phage generation time and help to define rates of phage population growth. Also controlling rates of phage population growth is the number of phage progeny produced per infection: the phage burst size. In this chapter we present protocols for determining phage growth parameters, particularly phage rate of adsorption, latent period, eclipse period, and burst size.

Complete nucleotide sequence of a P2 family lysogenic bacteriophage, ϕMhaA1-PHL101, from Mannheimia haemolytica serotype A1

The 34,525 nucleotide sequence of a double-stranded DNA bacteriophage (phiMhaA1-PHL101) from Mannheimia haemolytica serotype A1 has been determined. The phage encodes 50 open reading frames. Twenty-three of the proteins are similar to proteins of the P2 family of phages. Other protein sequences are most similar to possible prophage sequences from the draft genome of Histophilus somni 2336. Fourteen open reading frames encode proteins with no known homolog. The P2 orthologues are collinear in phiMhaA1-PHL101, with the exception of the phage tail protein gene T, which maps in a unique location between the S and V genes. The phage ORFs can be arranged into 17 possible transcriptional units and many of the genes are predicted to be translationally coupled. Southern blot analysis revealed phiMhaA1-PHL101 sequences in other A1 isolates as well as in serotype A5, A6, A9, and A12 strains of M. haemolytica, but not in the related organisms, Mannheimia glucosida or Pasteurella trehalosi.

Complete genomic nucleotide sequence of the temperate bacteriophage Aa Phi 23 of Actinobacillus actinomycetemcomitans

The entire double-stranded DNA genome of the Actinobacillus actinomycetemcomitans bacteriophage Aa Phi 23 was sequenced. Linear DNA contained in the phage particles is circularly permuted and terminally redundant. Therefore, the physical map of the phage genome is circular. Its size is 43,033 bp with an overall molar G+C content of 42.5 mol%. Sixty-six potential open reading frames (ORFs) were identified, including an ORF resulting from a translational frameshift. A putative function could be assigned to 23 of them. Twenty-three other ORFs share homologies only with hypothetical proteins present in several bacteria or bacteriophages, and 20 ORFs seem to be specific for phage Aa Phi 23. The organization of the phage genome and several genetic functions share extensive similarities to that of the lambdoid phages. However, Aa Phi 23 encodes a DNA adenine methylase, and the DNA packaging strategy is more closely related to the P22 system. The attachment sites of Aa Phi 23 (attP) and several A. actinomycetemcomitans hosts (attB) are 49 bp long.

Genes for tight adherence of Actinobacillus actinomycetemcomitans: from plaque to plague to pond scum

The Gram-negative periodontal pathogen Actinobacillus actinomycetemcomitans forms an extremely tenacious biofilm on solid surfaces such as glass, plastic and hydroxyapatite. This characteristic is likely to be important for colonization of the oral cavity and initiation of a potentially devastating form of periodontal disease. Genetic analysis has revealed a cluster of tad genes responsible for tight adherence to surfaces. Evidence indicates that the tad genes are part of a locus encoding a novel secretion system for the assembly and release of long, bundled Flp pili. Remarkably similar tad loci appear in the genomes of a wide variety of Gram-negative and Gram-positive bacteria, including many significant pathogens, and in Archaea. We propose that the tad loci are important for microbial colonization in a variety of environmental niches.

Identification of a cytolethal distending toxin gene locus and features of a virulence-associated region in Actinobacillus actinomycetemcomitans

A genetic locus for a cytolethal distending toxin (CDT) was identified in a polymorphic region of the chromosome of Actinobacillus actinomycetemcomitans, a predominant oral pathogen. The locus was comprised of three open reading frames (ORFs) that had significant amino acid sequence similarity and more than 90% sequence identity to the cdtABC genes of some pathogenic Escherichia coli strains and Haemophilus ducreyi, respectively. Sonic extracts from recombinant E. coli, containing the A. actinomycetemcomitans ORFs, caused the distension and killing of Chinese hamster ovary cells characteristic of a CDT. Monoclonal antibodies made reactive with the CdtA, CdtB, and CdtC proteins of H. ducreyi recognized the corresponding gene products from the recombinant strain. CDT-like activities were no longer expressed by the recombinant strain when an OmegaKan-2 interposon was inserted into the cdtA and cdtB genes. Expression of the CDT-like activities in A. actinomycetemcomitans was strain specific. Naturally occurring expression-negative strains had large deletions within the region of the cdt locus. The cdtABC genes were flanked by an ORF (virulence plasmid protein), a partial ORF (integrase), and DNA sequences (bacteriophage integration site) characteristic of virulence-associated regions. These results provide evidence for a functional CDT in a human oral pathogen.

Actinobacillus actinomycetemcomitans and Porphyromonas gingivalis in young Chinese adults

The aim of this study was to determine the presence or absence of Actinobacillus actinomycetemcomitans and Porphyromonas gingivalis in young Chinese adults and to examine the A. actinomycetemcomitans isolates from positive subjects with regard to the serotype distribution, presence of the leukotoxin gene lktA and the promoter for the leukotoxin operon as well as the incidence of phage Aa phi 23. Sixty subjects, working in a knitting factory in the Province of Guangzhou, People's Republic of China, were investigated. Subgingival microbial samples were taken from both upper first molars. They were cultured both anaerobically and in 5% CO2. P. gingivalis was found in 33 subjects. On average, it constituted 7% of the total anaerobic cultivable counts. A. actinomycetemcomitans was detected in 37 subjects of which seven yielded counts > 10(5). Twenty-one subjects were positive for both organisms. A. actinomycetemcomitans serotype a was found in 9 subjects, serotype c was found in 23 and serotype e in 5. A. actinomycetemcomitans serotypes b and d were not detected in any subjects. Presence of the leukotoxin gene lktA was demonstrated for all A. actinomycetemcomitans isolates; however, none of the A. actinomycetemcomitans strains from the present study had a deletion in the promoter region of the leukotoxin operon. The results of this investigation show a high frequency of the putative periodontal pathogens P. gingivalis and A. actinomycetemcomitans and corroborate the concept that there is variation in virulence and pathogenic potential among isolates from different subjects.

Functional analysis of pVT745, a plasmid from Actinobacillus actinomycetemcomitans

Plasmid pVT745 is a 25.1-kb replicon isolated from Actinobacillus actinomycetemcomitans strain VT745. A previous report described the hybridization of pVT745 in 5 strain-specific patterns to chromosomal DNA from 15 other A. actinomycetemcomitans strains. However, pVT745 does not share homology with the chromosome of the strain from which it was isolated, VT745. It was hypothesized that the shared areas of homology might represent insertion sequence elements and/or transposons possibly encoding resistance to one or more antibiotics. An antibiogram of strain VT745 demonstrated that this strain was uniformly susceptible to all antibiotics examined. Because insertion sequence elements and transposons are mobile genetic elements, a series of cell passaging experiments, followed by Southern hybridization was conducted in a attempt to detect transposition of pVT745 homologous DNA within the chromosomes of several A. actinomycetemcomitans strains. The results of these experiments suggested stability of the homologous DNA both within the chromosome and on the plasmid. It was also possible that pVT745 represented a lysogenic bacteriophage. Phage induction experiments were conducted under conditions that induced a previously described A. actinomycetemcomitans lysogenic phage, but no phage could be induced from strain VT745. Attempts to obtain isolates of VT745 cured of pVT745 were also unsuccessful.

Relationship of serotype, leukotoxin gene type and lysogeny in Actinobacillus actinomycetemcomitans to periodontal disease status

Actinobacillus actinomycetemcomitans has been associated with different forms of periodontitis, particularly with localized juvenile periodontitis (LJP). The bacterium possesses several virulence factors which have been shown to interact with the host immune system. Among these factors, leukotoxin, surface antigens (serotype) and bacteriophages have been suggested directly or indirectly to influence the course of infection. However, few studies have been able to show associations between these factors and periodontal disease, alone or in combination. Thus, the purpose of the present study was to investigate possible correlations between periodontal disease status and selected virulence factors (serotype, presence of bacteriophages, and the presence of a 530 bp deletion in the promoter region of the leukotoxin gene). 36 subjects took part in the study. Serotype c was the most frequently found serotype among periodontally affected subjects, although serotypes a and b were also present. 27 out of 36 strains harbored bacteriophages, and there was strong evidence that some of the bacteriophages were different from the previously characterized phi Aa phage. A. actinomycetemcomitans containing the F-fragment phage were more frequently associated with periodontal disease. Five strains, all serotype b, 3 from LJP patients and 2 from healthy subjects, showed a 530-bp deletion in the promoter region of the leukotoxin gene.

Presence of bacteriophage Aa phi 23 correlates with the population genetic structure of Actinobacillus actinomycetemcomitans

Several bacteriophages associated with the oral bacterium Actinobacillus actinomycetemcomitans have been identified. Lysogeny might affect the virulence of this bacterium, which has been implicated in the etiology of juvenile and adult periodontitis. We have determined the presence of bacteriophage Aa phi 23-related DNA sequences among 185 A. actinomycetemcomitans strains belonging to 2 well-characterized collections and have related the findings to the population genetic structure of the collections. 2 cloned Aa phi 23-specific DNA probes were used in Southern blot hybridization experiments to detect homologous sequences in whole-cell DNA of the strains. DNA from 65 (35%) of the 185 strains hybridized to either of the DNA probes. The majority (74%) of the hybridizing strains showed an identical hybridization pattern, indicating presence of phage Aa phi 23. Whole-cell DNA from the remaining hybridizing strains hybridized to the probes with different patterns, indicating that DNA sequences related to but different from phage Aa phi 23 occur in these strains. The majority (81%) of the strains which harbored phage Aa phi 23 were of serotype a, whereas serotype d strains appeared to be resistant to infection with this phage. There was a clear correlation between hybridization patterns and genetic subdivisions based on our previous population genetic analyses of A. actinomycetemcomitans. However, there was no significant correlation between occurrence of Aa phi 23 among A. actinomycetemcomitans strains and the periodontal status of the patients from whom the isolates were obtained, suggesting that this bacteriophage does not significantly influence the virulence of A. actinomycetemcomitans.

Transfection of Actinomyces spp. by genomic DNA of bacteriophages from human dental plaque

Bacteriophages that produced turbid or clear zones of lysis in strains of Actinomyces were isolated from 22 of 124 samples of fresh human dental plaque. All human and nonhuman strains of Actinomyces viscosus or Actinomyces naeslundii tested in this study were sensitive to infection by one or more of these phages. In contrast, none of the Actinomyces odontolyticus, Actinomyces israelii, or Actinomyces bovis strains tested were susceptible. Results of restriction endonuclease analyses indicated that the genomes of these phages consisted of double-stranded DNA molecules ranging in size between 16 and 60 kbp. Sequence homology under hybridization conditions of high stringency was observed among a few of the isolated phages. A lysogenized isolate of A. viscosus MG-1 was obtained following infection with a temperate phage, designated phi 225. Results of Southern blot analyses indicated that phi 225 replicated as a plasmid in the lysogenized strain. Genomic DNA from several lytic phages was used to establish conditions for transfection by electroporation of strains of Actinomyces spp. Efficiencies of DNA transfer ranged from 10(2) to 10(5) plaque-forming units per microgram of DNA were obtained under optimal transfection conditions. The results of these studies demonstrate that transfer of genetic information in Actinomyces spp. can be achieved by transfection.

Temperate bacteriophages are common among Actinobacillus actinomycetemcomitans isolates from periodontal pockets

Actinobacillus actinomycetemcomitans is a suspected etiologic agent in destructive periodontal diseases. The detection of bacteriophages in A. actinomycetemcomitans in the subgingival plaque of patients with rapidly destructive forms of periodontitis led to the hypothesis that bacteriophage infection might increase the virulence of this bacterium (19). A. actinomycetemcomitans was isolated from 68 subjects from the Netherlands and Switzerland with localized juvenile periodontitis, rapidly progressing periodontitis, or adult periodontitis, and was tested for the presence of temperate bacteriophage with the overlay plate technique. More than half of the A. actinomycetemcomitans strains were found to release bacteriophage which formed individual plaques on indicator strains. Electron microscopy of preparations from 7 strains revealed virions with an icosahedral head and a contractile tail typical for double-stranded DNA bacteriophages. The presence of A. actinomycetemcomitans carrying temperate bacteriophage was not correlated with the composition of the subgingival microflora nor with the clinical form of periodontal disease. Destructive periodontal disease of subjects with phage-carrying A. actinomycetemcomitans was not more severe than of subjects with phage-free A. actinomycetemcomitans as determined by several clinical parameters. In contrast, the pocket depth and the attachment loss were significantly lower for adult periodontitis subjects with phage-carrying A. actinomycetemcomitans. It seems unlikely that the frequently occurring temperate bacteriophages increase significantly the virulence of A. actinomycetemcomitans.

Inducible bacteriophages of Actinobacillus actinomycetemcomitans

Doses of 0.1 to 1.0 micrograms/ml of mitomycin C induced cell lysis of six of eight strains of Actinobacillus actinomycetemcomitans tested. Infectious phages were induced from ATCC strains 43717, 29524, 33384, and 43719; non-plaque-forming, possibly defective phages were induced from ATCC strains 29522 and 29523. No phages were detected in strain FDC 651 or ATCC strain 43718. No correlation between lysogeny and leukotoxin production or serotype of the strains could be established. Gel electrophoresis of phage DNAs indicated that the induced phages were of three types, based on size. By electron microscopy, the phages were found to belong to either morphotype A1 or morphotype B1; no other morphotypes were observed. Curing experiments led to the isolation of nonlysogenic derivatives of two strains, which supported plaque formation by the phages they originally carried. On the basis of our results, lysogeny appears to be widespread in A. actinomycetemcomitans.

Prevalence and distribution of bacteriophage phi Aa DNA in strains of Actinobacillus actinomycetemcomitans

phi Aa is a bacteriophage that was originally isolated by induction of a lysogenic strain of the oral bacterium Actinobacillus actinomycetemcomitans. Since the discovery of phage phi Aa, additional phages infecting several other strains of A. actinomycetemcomitans have been identified. To determine the prevalence of phi Aa or phi Aa-related temperate phages in this species, a phi Aa-specific DNA probe was prepared to screen for homologous sequences among 42 strains of A. actinomycetemcomitans. Fourteen (33%) of the 42 strains examined contained DNA sequences that hybridized with the phage phi Aa probe. A bacteriophage designated phi Aa33384 was isolated by induction from one of the strains (ATCC 33384) that contained a sequence that hybridized with the phi Aa probe. The phi Aa probe hybridized with the DNA extracted from bacteriophage phi Aa33384. The distribution of the phage phi Aa sequence among A. actinomycetemcomitans serotypes was 5/13 (38%) of the serotype a strains, 0/16 (0%) of the serotype b strains, and 9/13 (69%) of the serotype c strains. The results of this investigation suggest that the target sequence prepared from the phage phi Aa genome is fairly common in the A. actinomycetemcomitans chromosome, and that the sequence is distributed among the A. actinomycetemcomitans serotypes in a seemingly nonrandom manner.

Electron microscopy of phages in serotypes of Actinobacillus actinomycetemcomitans

Actinobacillus actinomycetemcomitans, Actinobacillus ureae, Haemophilus aphrophilus, Haemophilus paraphrophilus, Haemophilus influenzae, Haemophilus parainfluenzae, Pasteurella haemolytica and Pasteurella multocida strains were examined by transmission electron microscopy for the presence of bacteriophages. Phages were detected in serotype a (SUNY 75) and e (UOH 1705) and in the fresh clinical isolates UOH Q1243 and UOH Q1247 of A. actinomycetemcomitans. Phages were not found in serotype b, c and d strains of A. actinomycetemcomitans, in the fresh clinical isolate UOH Q1244 of this species or in old strains (including reference strains) of related species from the Actinobacillus-Haemophilus-Pasteurella group.

Identification of Actinobacillus actinomycetemcomitans: polymerase chain reaction amplification of lktA-specific sequences

Actinobacillus actinomycetemcomitans has been strongly implicated in the etiology of localized juvenile periodontitis. Techniques used in the identification of this periodontal pathogen include cultural, biochemical, immunological and DNA hybridization analysis. In this study, we report the use of polymerase chain reaction (PCR) to amplify unique sequences of A. actinomycetemcomitans. Specific oligonucleotide primers LKT2 and LKT3 were designed to hybridize to the A. actinomycetemcomitans lktA gene, which encodes leukotoxin, a putative A. actinomycetemcomitans virulence factor. The LKT2 and LKT3 primers amplified lktA-specific sequences from all 12 A. actinomycetemcomitans strains tested. In another set of experiments, 13 other bacterial species, most of which are normal residents of the oral cavity, were tested with these primers. These PCR amplifications also contained 2 additional primers, RRN4 and RRN5, which served as positive controls; RRN4 and RRN5 were designed to amplify specific sequences of eubacterial 16S ribosomal DNA (rDNA). PCR amplifications of all bacterial species tested, including A. actinomycetemcomitans, yielded 16S rDNA-specific DNA fragments. Furthermore, each bacterial species tested, with the exception of A. actinomycetemcomitans, failed to amplify lktA sequences. The LKT and RRN primers were used in further PCR experiments to detect A. actinomycetemcomitans directly from gingival fluid samples. The results clearly demonstrate the simplicity, rapidity, specificity and accuracy of the LKT primers in the identification of A. actinomycetemcomitans.

Characterization and physical mapping of the genome of bacteriophage phi Aa from Actinobacillus actinomycetemcomitans

The size, configuration and restriction map of Actinobacillus actinomycetemcomitans bacteriophage phi Aa DNA was determined by means of restriction endonuclease analysis. Digestion of the phi Aa DNA with restriction enzymes Hind III, Eco RI and Sal I produced 6, 5, and 4 fragments, respectively. Based upon the sum of the sizes of the restriction fragments of these enzymes, the DNA was estimated to be 47.2 kilobase pairs in length. A restriction map was constructed using Hind III and Sal I. Incubation with exonuclease Bal 31 for increasing lengths of time resulted in progressive hydrolysis of the DNA, as expected for a linear molecule. No sub-molar fragments or diffuse bands were observed in the agarose gels of the restriction endonuclease digests of the phi Aa DNA. Attempts at ligating the ends of the DNA were consistently unsuccessful. Therefore, we found no evidence for cohesive ends, a circular permutation of the genome or for headful packaging mechanism from a concatameric DNA precursor.

Structural proteins of the Actinobacillus actinomycetemcomitans bacteriophage phi Aa

øAa is an A1 morphotype bacteriophage which infects certain strains of Actinobacillus actinomycetemcomitans. Sodium dodecyl sulfate-polyacrylamide gel electrophoresis (SDS-PAGE) analysis of dissociated, purified phi Aa particles revealed 7 major structural proteins (P1-P7) ranging in size from 17.5 to 52.7 kilodaltons (Kd). Treatment of the intact phage particles with 67% dimethyl sulfoxide (DMSO) resulted in the separation of the virion head and tail subunits. Purification of the head subunits was accomplished by sucrose density gradient centrifugation of the DMSO-treated phage particles. The purified head subunits were composed of a single protein having an electrophoretic mobility which corresponded to a 39.5 Kd protein (P3) of the intact virus. Raising the pH of a purified phi Aa suspension to 12.7 disrupted the head subunits, as well as the tail tube and tail fibers, releasing intact contractile tail sheaths. The tail sheaths were collected by centrifugation. The purified tail sheaths were analyzed by SDS-PAGE and were found to be composed of two proteins (P1 and P2) having molecular weights of 52.7 and 41.2 Kd respectively. The location of each of the 4 remaining major structural proteins in the phi Aa virion remains to be determined.

The comparative cytotoxicity of periodontal bacteria

The direct cytotoxicity of sonic extracts (SE) from nine periodontal bacteria for human gingival fibroblasts (HGF) was compared. Equivalent dosages (in terms of protein concentration) of SE were used to challenge HGF cultures. The cytotoxic potential of each SE was assessed by its ability to (1) inhibit HGF proliferation, as measured by direct cell counts; (2) inhibit 3H-thymidine incorporation in HGF cultures; or (3) cause morphological alterations of the cells in challenged cultures. The highest concentration (500 micrograms SE protein/ml) of any of the SEs used to challenge the cells was found to be markedly inhibitory to the HGFs by all three of the criteria of cytotoxicity. At the lowest dosage tested (50 micrograms SE protein/ml); only SE from Actinobacillus actinomycetemcomitans, Bacteroides gingivalis, and Fusobacterium nucleatum caused a significant effect (greater than 90% inhibition or overt morphological abnormalities) in the HGFs as determined by any of the criteria employed. SE from Capnocytophaga sputigena, Eikenella corrodens, or Wolinella recta also inhibited cell proliferation and thymidine incorporation at this dosage; however, the degree of inhibition (5-50%) was consistently, clearly less than that of the first group of three organisms named above. The SE of the three other organisms tested (Actinomyces odontolyticus, Bacteroides intermedius, and Streptococcus sanguis) had little or no effect (0-10% inhibition) at this concentration. The data suggest that the outcome of the interaction between bacterial components and normal resident cells of the periodontium is, at least in part, a function of the bacterial species.

Use of lytic bacteriophage for Actinomyces viscosus T14V as a probe for cell surface components mediating intergeneric coaggregation

A lytic bacteriophage for Actinomyces viscosus T14V (the reference strain for actinomyces coaggregation group A) was isolated from raw sewage. This phage, designated BF307, also lysed the T14V-derived nonfimbriated mutant PK455-2 as well as A. viscosus MG-1 and T14AV but not the other serotype 2 or serotype 1 strains of this species that were tested or any of nine Actinomyces naeslundii isolates. Phages BF307 belonged to Bradley morphological group C and was similar in appearance to the A. viscosus MG-1 phages Av-1 and Av-3, which do not productively infect A. viscosus T14V. A. viscosus MG-1 mutants selected for resistance to phage BF307, Av-3, or CT7 (a human dental plaque isolate with the same host range as BF307) were coresistant to the other two phages but sensitive to Av-1. These results indicate that the receptors on A. viscosus MG-1 for phages BF307, Av-3, and CT7 are identical or share a common precursor and that the receptor for phage Av-1 is distinct. Comparison of the genomes of BF307, Av-3, and CT7 revealed that their DNAs were similar in size but distinguishable by restriction analysis. Two altered coaggregation phenotypes were identified among the phage BF307-resistant mutants of strains MG-1, T14V, T14AV, and PK455-2. Class I mutants had lost the ability to interact with coaggregation group 1 streptococci, and class II mutants did not coaggregate with either group 1 or group 2 streptococci. These results are consistent with the proposal that the phage BF307 receptor on these A. viscosus strains is related to one of the structures that mediates coaggregation with oral streptococci. A model to delineate the various coaggregation mediators on the surface of actinomyces coaggregation group A cells is presented, and the use of these phages to probe surface components of human oral actinomyces strains is discussed.

The presence of phage-infected Actinobacillus actinomycetemcomitans in localized juvenile periodontitis patients

Electron microscopy revealed 2 different types of bacteriophages isolated from Actinobacillus actinomycetemcomitans colonizing exclusively diseased sites in 4 patients with localized juvenile periodontitis (LJP). All sites infected with phage were undergoing periodontal destruction, as judged from consecutive routine radiographs. The phages isolated had a wide host range as assessed from their ability to infect a series of reference strains of A. actinomycetemcomitans. A 5th patient harboured non-infected A. actinomycetemcomitans in a surgically treated site which had undergone no bone destruction during the last 12 months. The present findings suggested that the pathogenic potential of A. actinomycetemcomitans in LJP may increase due to phage infection.

The use of DNA probes in dental diagnosis and therapy

Recombinant DNA technology now allows for the development of genetic probes specific for a growing number of etiologic disease agents, including those suspected pathogens in the oral environment. The increasing refinement of DNA probe methodologies and sensitivities will ultimately permit their commonplace use with clinical samples for the rapid identification of their bacterial compositions. The use of probe technology potentially offers a much more facile, accurate, and less time-consuming mechanism for the identification of fastidious micro-organisms from the oral cavity, many of which are laborious and difficult to cultivate.

Leukotoxic activity in Actinobacillus (Haemophilus) actinomycetemcomitans isolated from periodontal disease patients

Leukotoxic activity in Actinobacillus (Haemophilus) actinomycetemcomitans isolated from patients with rapidly progressive periodontitis (RP), gingivitis (G), and juvenile periodontitis (JP), and several oral bacteria, was determined by observation of morphological changes in polymorphonuclear leukocytes (PMNs). Many A. actinomycetemcomitans isolates yielded both rough-surfaced and umbonate-shaped colonies (A-type), and smooth-surfaced and convex-shaped colonies (B-type), when stock cultures were streaked on agar medium. Both types of cells were identical in terms of Gram stain, cell morphology, sugar fermentation profile, nitrate reduction and cellular fatty acid composition. Sonic extracts were prepared from 32 A. actinomycetemcomitans strains isolated from patients and from 3 American Type Culture Collection (ATCC) strains. Sonic extracts from 8 isolates and 2 ATCC strains induced sphering of PMNs during a 45-50 min period of incubation at 37 C. Extracts from the other oral bacteria had no effects on PMN morphology. The sphered PMNs were found by their fluorochromatic-negative reactions to be damaged cells. The leukotoxic substance was heat-sensitive (56 C, 30 min), trypsin-sensitive and did not induce sphering of PMNs at 4 C. There was no clear correlation between colony type and leukotoxicity. Among 8 leukotoxic strains, 5 were isolates from an RP patient.

Association between bacteriophage-infected Actinobacillus actinomycetemcomitans and rapid periodontal destruction

Actinobacillus actinomycetemcomitans was isolated from periodontal pockets in a patient suffering from prepubertal periodontitis. Electron microscopy revealed 3 different groups of bacteriophages in filtrates of subgingival plaque from all the active periodontal lesions. Phage infected A. actinomycetemcomitans in this patient was restricted to periodontal pockets which, according to standardized roentgenograms, had shown bone destruction during the past 12 months. A follow-up study of 7 months revealed that a "burned out" site which harbored noninfected A. actinomycetemcomitans, turned into an active site at the same time as the A. actinomycetemcomitans of that site became infected with the phages. These findings indicate a relationship between rapid prepubertal periodontal destruction and phage-infected A. actinomycetemcomitans.

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

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

Bacteriophage infection--a possible mechanism for increased virulence of bacteria associated with rapidly destructive periodontitis

We have recently isolated several groups of bacteriophages infecting Actinobacillus actinomycetemcomitans from periodontal lesions in patients with rapidly destructive periodontitis. Bacteriophage infection of these bacteria in these patients was restricted to periodontal pockets showing radiographic evidence of recent bone loss and suggests an association between phage-infected A. actinomycetemcomitans and active periodontal disease. On the basis of the biological activity of bacteriophages we propose a working hypothesis to explain the mechanism by which a phage may increase bacterial virulence in periodontal disease.

Isolation of Actinomyces bacteriophage from human dental plaque

Human dental plaque samples were screened for the presence of bacteriophage for Actinomyces viscosus and Streptococcus sanguis. None of the 336 samples yielded phage for S. sanguis, but 10 contained virulent actinomyces phage. A high host cell specificity was observed in that one phage isolate infected only A. viscosus T14V, eight phage isolates infected only A. viscosus MG-1, and one infected both strains. None was capable of productively infecting various other actinomyces strains that represented the six actinomyces coaggregation groups. Because phage-containing samples occurred randomly in this survey, no correlation between the individual collecting the samples, dental clinic, or type of patient and the presence of phage in the sample was noted. Examination of one of the samples that yielded phage for the presence of a natural host strain for that particular phage resulted in the isolation of two strains which were identified as A. viscosus serotype II and Actinomyces naeslundii serotype I. This is the first report of an A. naeslundii host strain and actinomyces bacteriophage of human dental plaque origin. The finding of both phage and host strains in the same dental plaque sample along with the observation of high host cell specificity by these phage provide indicators that support an active role for actinomyces bacteriophage in oral microbial ecology. The use of these freshly isolated phage as probes to study actinomyces coaggregation properties is discussed.

Lysozyme-mediated aggregation and lysis of the periodontal microorganism Capnocytophaga gingivalis 2010

The ability of lysozyme to aggregate and lyse the gram-negative capnophilic periodontal microorganism Capnocytophaga gingivalis 2010 was monitored optically at 540 nm. Both hen egg white and chromatographically purified human lysozymes had significant but similar aggregation potentials for both logarithmic- and stationary-phase bacteria. In general, an increase in enzyme concentration resulted in a graded increase in both the initial and maximum changes in turbidity which occurred during the reaction period. The greatest change in turbidity occurred within the initial minutes of interaction of lysozyme and the cells, and the extent of aggregation paralleled a rapid depletion of lysozyme by the suspensions during the first minute of its incubation with the bacteria. Interestingly, the muramidase inhibitors N-acetyl-D-glucosamine and histamine did not block aggregation, whereas maleylation of lysozyme completely inhibited its aggregating ability. Demaleylation, however, restored aggregation activity comparable to the native enzyme, indicating that maleylated lysozyme retained its integrity and that aggregation was primarily dependent on charge. The addition of up to physiological concentrations of NaHCO3 and NaCl to cell aggregates resulted in varying degrees of deaggregation and lysis. Surprisingly, ultrastructural analysis of lysozyme-treated cells revealed morphological changes with or without the addition of salt. Damage appeared to occur at the blunted polar end of the cells where there was a large spherical outpouching bordered by a damaged cell envelope. Damaged cells uniformly contained dense granular cytoplasmic debris. In effect, the cationic enzyme lysed C. gingivalis 2010, which was not apparent in the spectrophotometric assay. The paradoxical finding that during bacterial aggregation there was lysis may be of significance to the further elucidation of lysozyme's antibacterial role in the gingival sulcus.

Actinobacillus actinomycetemcomitans in human periodontal disease

Recent evidence implicates Actinobacillus actinomycetemcomitans in the etiology of localized juvenile periodontitis. This paper reviews the morphological, biochemical and serological charcteristics of A. actinomycetemcomitans, evidence incriminating it as a periodontopathogen, its importance in human nonoral infections, and virulence factors which may be involved in the pathogenesis of A. actinomycetemcomitans infections. A. actinomycetemcomitans is a non-motile, gram-negative, capnophilic, fermentative coccobacillus which closely resembles several Haemophilus species but which does not require X or V growth factors. The organism has been categorized into 10 biotypes based on the variable fermentation of dextrin, maltose, mannitol, and xylose and into 3 serotypes on the basis of heat stable, cell surface antigens. A. actinomycetemcomitans' primary human ecologic niche is the oral cavity. It is found in dental plaque, in periodontal pockets, and buccal mucosa in up to 36% of the normal population. The organism can apparently seed from these sites to cause severe infections throughout the human body such as brain abscesses and endocarditis. There is a large body of evidence which implicates A. actinomycetemcomitans as an important micro-organism in the etiology of localized juvenile periodontitis including: (1) an increased prevalence of the organism in almost all localized juvenile periodontitis patients and their families compared to other patient groups; (2) the observation that localized juvenile periodontitis patients exhibit elevated antibody levels to A. actinomycetemcomitans in serum, saliva and gingival crevicular fluid; (3) the finding that localized juvenile periodontitis can be successfully treated by eliminating A. actinomycetemcomitans from periodontal pockets; (4) histopathologic investigations showing that A. actinomycetemcomitans invades the gingival connective tissue in localized juvenile periodontitis lesions; (5) the demonstration of several pathogenic products from A. actinomycetemcomitans including factors which may: (a) facilitate its adherence to mucosal surfaces such as capsular polysaccharides; (b) inhibit host defense mechanisms including leukotoxin, a polymorphonuclear leukocyte chemotaxis inhibiting factor, and a lymphocyte suppressing factor (c) cause tissue destruction such as lipopolysaccharide endotoxin, a bone resorption-inducing toxin, acid and alkaline phosphatases, collagenase, a fibroblast inhibiting factor and an epitheliotoxin.(ABSTRACT TRUNCATED AT 400 WORDS)

Lytic sensitivity of Actinobacillus actinomycetemcomitans Y4 to lysozyme

The ability of both human and hen egg white lysozymes to lyse Actinobacillus actinomycetemcomitans Y4 was investigated. Lysis was followed optically at 540 nm by measuring the percent reduction in turbidity of freshly harvested log-phase cells suspended in Tris-maleate buffers within a wide range of pH (5.2 to 8.5) and molarity (0.01 to 0.2 M) and containing various amounts of enzyme and EDTA. In several instances, treated microorganisms were subsequently examined in thin sections by electron microscopy. Reductions in turbidity and clearing of suspensions occurred with small amounts of lysozyme (less than 1 microgram) under relatively alkaline conditions and at low ionic strength and in the presence of small amounts of EDTA (greater than 0.01 mM). Under the most alkaline conditions, EDTA alone effected turbidity reductions similar to those observed in the presence of lysozyme, which suggested that EDTA not only increased outer membrane permeability but also caused cell lysis. Ultrastructural analysis did not always correspond to turbidimetric observations. Cell lysis was virtually complete in suspensions containing both lysozyme and EDTA. However, in contrast to turbidimetric findings, a significant percentage of cells (greater than 25%) was lysed in the presence of lysozyme alone. Furthermore, significant damage occurred in the presence of EDTA alone. Spheroplast-like cell ghosts were present which surrounded condensed cytoplasm or relatively clear spaces. These findings further support the concept of the requirement for electron microscopy to assess lytic damage in addition to turbidimetric and biochemical methods. Our results are the first to demonstrate the remarkable sensitivity of A. actinomycetemcomitans Y4 to lysozyme and to show that EDTA not only affects outer membrane permeability but effects cell lysis, possibly through activation of autolytic enzymes at the cytoplasmic membrane. The exquisite sensitivity of A. actinomycetemcomitans Y4 to lysis could be an important mechanism by which lysozyme participates in the regulation of this suspected periodontal pathogen.