C. N. Lau

Bio: C. N. Lau is an academic researcher from The Forsyth Institute. The author has contributed to research in topics: Treponema denticola & Treponema. The author has an hindex of 5, co-authored 5 publications receiving 2661 citations.

Bacterial Diversity in Human Subgingival Plaque

Abstract: The purpose of this study was to determine the bacterial diversity in the human subgingival plaque by using culture-independent molecular methods as part of an ongoing effort to obtain full 16S rRNA sequences for all cultivable and not-yet-cultivated species of human oral bacteria. Subgingival plaque was analyzed from healthy subjects and subjects with refractory periodontitis, adult periodontitis, human immunodeficiency virus periodontitis, and acute necrotizing ulcerative gingivitis. 16S ribosomal DNA (rDNA) bacterial genes from DNA isolated from subgingival plaque samples were PCR amplified with all-bacterial or selective primers and cloned into Escherichia coli. The sequences of cloned 16S rDNA inserts were used to determine species identity or closest relatives by comparison with sequences of known species. A total of 2,522 clones were analyzed. Nearly complete sequences of approximately 1,500 bases were obtained for putative new species. About 60% of the clones fell into 132 known species, 70 of which were identified from multiple subjects. About 40% of the clones were novel phylotypes. Of the 215 novel phylotypes, 75 were identified from multiple subjects. Known putative periodontal pathogens such as Porphyromonas gingivalis, Bacteroides forsythus, and Treponema denticola were identified from multiple subjects, but typically as a minor component of the plaque as seen in cultivable studies. Several phylotypes fell into two recently described phyla previously associated with extreme natural environments, for which there are no cultivable species. A number of species or phylotypes were found only in subjects with disease, and a few were found only in healthy subjects. The organisms identified only from diseased sites deserve further study as potential pathogens. Based on the sequence data in this study, the predominant subgingival microbial community consisted of 347 species or phylotypes that fall into 9 bacterial phyla. Based on the 347 species seen in our sample of 2,522 clones, we estimate that there are 68 additional unseen species, for a total estimate of 415 species in the subgingival plaque. When organisms found on other oral surfaces such as the cheek, tongue, and teeth are added to this number, the best estimate of the total species diversity in the oral cavity is approximately 500 species, as previously proposed.

The diversity of periodontal spirochetes by 16S rRNA analysis

Abstract: The purpose of this study was to examine the diversity of spirochetes in the subgingival pocket of multiple subjects with a range of periodontal conditions, including two healthy, one adult periodontitis, three acute necrotizing ulcerative gingivitis, eight refractory periodontitis, and one human immunodeficiency virus (HIV) periodontitis. The 16S rRNA genes of spirochetes in plaque were amplified by polymerase chain reaction using spirochete selective primers. Over 500 clones were sequenced and subjected to phylogenetic analysis. The sequences clustered into the 10 known cultivated Treponema species and into 47 as-yet-uncultivated Treponema species. Most of these Treponema species were identified from multiple clones and subjects. The human periodontal pocket harbors a highly diverse treponeme population. Of the cultivated species, Treponema denticola, Treponema maltophilum and Treponema sp. Smibert-3 were most commonly encountered in diseased subjects but rarely in healthy subjects. Molecular tools based on the sequence data from this study will allow determination of the prevalence of cultivable and uncultivable treponemes in oral diseases.

Prevalent Bacterial Species and Novel Phylotypes in Advanced Noma Lesions

Abstract: The purpose of this study was to determine the bacterial diversity in advanced noma lesions using culture-independent molecular methods. 16S ribosomal DNA bacterial genes from DNA isolated from advanced noma lesions of four Nigerian children were PCR amplified with universally conserved primers and spirochetal selective primers and cloned into Escherichia coli. Partial 16S rRNA sequences of approximately 500 bases from 212 cloned inserts were used initially to determine species identity or closest relatives by comparison with sequences of known species or phylotypes. Nearly complete sequences of approximately 1,500 bases were obtained for most of the potentially novel species. A total of 67 bacterial species or phylotypes were detected, 25 of which have not yet been grown in vitro. Nineteen of the species or phylotypes, including Propionibacterium acnes, Staphylococcus spp., and the opportunistic pathogens Stenotrophomonas maltophilia and Ochrobactrum anthropi were detected in more than one subject. Other known species that were detected included Achromobacter spp., Afipia spp., Brevundimonas diminuta, Capnocytophaga spp., Cardiobacterium sp., Eikenella corrodens, Fusobacterium spp., Gemella haemoylsans, and Neisseria spp. Phylotypes that were unique to noma infections included those in the genera Eubacterium, Flavobacterium, Kocuria, Microbacterium, and Porphyromonas and the related Streptococcus salivarius and genera Sphingomonas and TREPONEMA: Since advanced noma lesions are infections open to the environment, it was not surprising to detect species not commonly associated with the oral cavity, e.g., from soil. Several species previously implicated as putative pathogens of noma, such as spirochetes and Fusobacterium spp., were detected in at least one subject. However, due to the limited number of available noma subjects, it was not possible at this time to associate specific species with the disease.

Phylogenetic analysis of cultivable oral treponemes from the Smibert collection

Abstract: Dr Robert Smibert from the Virginia Polytechnic Institute, USA, isolated and collected over 200 strains of oral treponemes over a 20-year period. Dr Smibert, Dr W. E. C. Moore and Dr L. V. Moore separated these isolates and reference strains into different groups on the basis of cellular fatty acid analysis. In this study, the 16S rRNA genes were sequenced for 47 strains that were representative of these groups. Five distinct species were identified on the basis of 16S rRNA sequence comparisons; two of these species are newly named and three have not yet been characterized. The first species, designated Treponema Smibert-1, was represented by the single strain D4B-1 and was later identified as the newly described Treponema maltophilum. However, strain D4B-1 possessed a different flagellar arrangement to that of T. maltophilum. The second species, Treponema Smibert-2, was represented by nine isolates that possessed identical 16S rRNA gene sequences. The closest relatives of this species were Treponema Smibert-3 and Treponema Smibert-4 at approximately 90% sequence similarity. Within Treponema Smibert-2, there was no correlation between phylogenetic analysis and cellular fatty acid analysis since six different cellular fatty acid groups represented the nine strains. Treponema Smibert-3 (strain D36ER-1) and Treponema Smibert-4 (D62CR-12) were each represented by only a single strain and were closely related to each other at 98% sequence similarity. Strain D36ER-1 of Treponema Smibert-3 was identified as belonging to the not-yet-cultivated phylotype 20 [Choi, B. K., Paster, B. J., Dewhirst, F. E. & Gobel, U. B. (1994). Infect Immun 62,1889–1895]. Strain D62CR-12 of Treponema Smibert-4 was nearly identical in sequence to the newly described Treponema amylovorum. The fifth species, Treponema Smibert-5, was represented by a single strain, D120CR-1, and was closely related at about 98% sequence similarity to the three subspecies of Treponema socranskii. The phylogenetic analyses of strains of Treponema vincentii and of subspecies of T. socranskii are also reported. The closest oral relatives of T. vincentii were Treponema medium at 98·7% sequence similarity and Treponema denticola at 91·5% sequence similarity. T. socranskii subspp. socranskii, buccale and paredis formed three separate phylogenetic branches with sequence similarities of about 98% to each other. The closest relative of the subspecies of T. socranskii and of Smibert-5 was Smibert-2 at about 86% sequence similarity. Historic reference strains Fuji, ‘Treponema ambigua’, Fm, lchelson-2, N-39, TD2, TRRD, MRB, IPP, Jethro and T32A, as well as an unknown strain designated only as Treponema oralis, were identified as strains of T. denticola. Reference strains Fuji, Jethro, T32A and IPP plus three isolates of the Smibert collection were also contaminated with a mycoplasma as determined by 16S rRNA comparative analysis. Consequently, spirochaetal cultures should be screened for mycoplasmas. There are presently at least ten species of cultivable oral species of Treponema with the cut-off for separate species

Defining the Normal Bacterial Flora of the Oral Cavity

Abstract: More than 700 bacterial species or phylotypes, of which over 50% have not been cultivated, have been detected in the oral cavity. Our purposes were (i) to utilize culture-independent molecular techniques to extend our knowledge on the breadth of bacterial diversity in the healthy human oral cavity, including not-yet-cultivated bacteria species, and (ii) to determine the site and subject specificity of bacterial colonization. Nine sites from five clinically healthy subjects were analyzed. Sites included tongue dorsum, lateral sides of tongue, buccal epithelium, hard palate, soft palate, supragingival plaque of tooth surfaces, subgingival plaque, maxillary anterior vestibule, and tonsils. 16S rRNA genes from sample DNA were amplified, cloned, and transformed into Escherichia coli. Sequences of 16S rRNA genes were used to determine species identity or closest relatives. In 2,589 clones, 141 predominant species were detected, of which over 60% have not been cultivated. Thirteen new phylotypes were identified. Species common to all sites belonged to the genera Gemella, Granulicatella, Streptococcus, and Veillonella. While some species were subject specific and detected in most sites, other species were site specific. Most sites possessed 20 to 30 different predominant species, and the number of predominant species from all nine sites per individual ranged from 34 to 72. Species typically associated with periodontitis and caries were not detected. There is a distinctive predominant bacterial flora of the healthy oral cavity that is highly diverse and site and subject specific. It is important to fully define the human microflora of the healthy oral cavity before we can understand the role of bacteria in oral disease.

The Human Oral Microbiome

Abstract: The human oral cavity contains a number of different habitats, including the teeth, gingival sulcus, tongue, cheeks, hard and soft palates, and tonsils, which are colonized by bacteria. The oral microbiome is comprised of over 600 prevalent taxa at the species level, with distinct subsets predominating at different habitats. The oral microbiome has been extensively characterized by cultivation and culture-independent molecular methods such as 16S rRNA cloning. Unfortunately, the vast majority of unnamed oral taxa are referenced by clone numbers or 16S rRNA GenBank accession numbers, often without taxonomic anchors. The first aim of this research was to collect 16S rRNA gene sequences into a curated phylogeny-based database, the Human Oral Microbiome Database (HOMD), and make it web accessible (www.homd.org). The HOMD includes 619 taxa in 13 phyla, as follows: Actinobacteria, Bacteroidetes, Chlamydiae, Chloroflexi, Euryarchaeota, Firmicutes, Fusobacteria, Proteobacteria, Spirochaetes, SR1, Synergistetes, Tenericutes, and TM7. The second aim was to analyze 36,043 16S rRNA gene clones isolated from studies of the oral microbiota to determine the relative abundance of taxa and identify novel candidate taxa. The analysis identified 1,179 taxa, of which 24% were named, 8% were cultivated but unnamed, and 68% were uncultivated phylotypes. Upon validation, 434 novel, nonsingleton taxa will be added to the HOMD. The number of taxa needed to account for 90%, 95%, or 99% of the clones examined is 259, 413, and 875, respectively. The HOMD is the first curated description of a human-associated microbiome and provides tools for use in understanding the role of the microbiome in health and disease.

Prevention of Infective Endocarditis Guidelines From the American Heart Association: A Guideline From the American Heart Association Rheumatic Fever, Endocarditis, and Kawasaki Disease Committee, Council on Cardiovascular Disease in the Young, and the Council on Clinical Cardiology, Council on Cardiovascular Surgery and Anesthesia, and the Quality of Care and Outcomes Research Interdisciplinary Working Group

Abstract: Background— The purpose of this statement is to update the recommendations by the American Heart Association (AHA) for the prevention of infective endocarditis that were last published in 1997. Met...

Bacterial Diversity in Human Subgingival Plaque

Abstract: The purpose of this study was to determine the bacterial diversity in the human subgingival plaque by using culture-independent molecular methods as part of an ongoing effort to obtain full 16S rRNA sequences for all cultivable and not-yet-cultivated species of human oral bacteria. Subgingival plaque was analyzed from healthy subjects and subjects with refractory periodontitis, adult periodontitis, human immunodeficiency virus periodontitis, and acute necrotizing ulcerative gingivitis. 16S ribosomal DNA (rDNA) bacterial genes from DNA isolated from subgingival plaque samples were PCR amplified with all-bacterial or selective primers and cloned into Escherichia coli. The sequences of cloned 16S rDNA inserts were used to determine species identity or closest relatives by comparison with sequences of known species. A total of 2,522 clones were analyzed. Nearly complete sequences of approximately 1,500 bases were obtained for putative new species. About 60% of the clones fell into 132 known species, 70 of which were identified from multiple subjects. About 40% of the clones were novel phylotypes. Of the 215 novel phylotypes, 75 were identified from multiple subjects. Known putative periodontal pathogens such as Porphyromonas gingivalis, Bacteroides forsythus, and Treponema denticola were identified from multiple subjects, but typically as a minor component of the plaque as seen in cultivable studies. Several phylotypes fell into two recently described phyla previously associated with extreme natural environments, for which there are no cultivable species. A number of species or phylotypes were found only in subjects with disease, and a few were found only in healthy subjects. The organisms identified only from diseased sites deserve further study as potential pathogens. Based on the sequence data in this study, the predominant subgingival microbial community consisted of 347 species or phylotypes that fall into 9 bacterial phyla. Based on the 347 species seen in our sample of 2,522 clones, we estimate that there are 68 additional unseen species, for a total estimate of 415 species in the subgingival plaque. When organisms found on other oral surfaces such as the cheek, tongue, and teeth are added to this number, the best estimate of the total species diversity in the oral cavity is approximately 500 species, as previously proposed.