Molecular and phenotypic characteristics of the genus actinomyces with particular reference to the human oral cavity
Abstract of thesis entitled
MOLECULAR AND PHENOTYPIC CHARACTERISTICS OF THE GENUS ACTINOMYCES WITH PARTICULAR REFERENCE TO THE HUMAN ORAL CAVITY
Submitted by Gaoyan TANG
For the degree of Doctor of Philosophy at the University of Hong Kong
in June 2004
Bacteria belonging to the genus Actinomyces comprise a group of either facultative or obligate anaerobic, non-spore-forming, non-motile, and Gram-positive pleomorphic rods. They are an important category of autochthonous, oro-intestinal bacteria both in humans and animals.
In order to accurately differentiate Actinomyces spp., oligonucleotide probes were developed for A. bovis, A. gerencseriae, A israelii, A. meyeri, A. odontolyticus, A. naeslundii genospecies 1 (cross-reacting with catalasenegative genospecies 2) and A. viscosus (cross-reacting with catalasepositive A. naeslundii genospecies 2, previously A. viscosus serotype II). Mter verifying the specificity and sensitivity, these probes were used for
Abstract evaluating associations between Actinomyces spp. and caries and,
The investigation of Actinomyces spp. in supragingival plaque from 17 caries-free and 36 caries-active children using the developed probes indicated that A. odontolyticus, A. naeslundii and A. gerencseriae contributed to supragingival plaque development, and might contribute, directly or indirectly to childhood caries initiation. Further, a higher prevalence and proportions of A. naeslundii genospecies 2, compared with genospecies 1 were noted in these plaque samples. The predominance and highly genetic diversity of genospecies 2 tend to suggest that it may contribute to the initiation of childhood caries.
Endodontic infection is a sequel of the carious process and, Actinomyces spp. are considered prime mediators of this common disease. Southern hybridization data from 32 endodontic infections, using the probes developed, indicated that A. odontolyticus was particularly common In diseased pulp chambers associated with caries, whilst catalase-negative A. naeslundii was more common in pulp infections with a history of trauma.
One advantage of molecular detection techniques over the traditional culture techniques is their superior ability to detect dormant bacteria. The susceptibility of endodontic organisms to routine, one-week, root canal
Abstract medication with either calcium hydroxide or Septomixine, was directly
evaluated using polymerase chain reaction and Southern hybridization with the probes described above. No significant difference in antimicrobial efficacy between calcium hydroxide and Septomixine was found either with regard to the total bacterial load or the quality of the Actinomyces spp. detected. Thus, in clinical terms this study tends to imply that the routine one-week, endodontic medication with either of these drugs may not totally eliminate, residual intra -canal bacteria.
Actinomyces colonization, either within or outside root canals is considered to be facilitated by fimbriae on their cell surfaces. When examined using atomic force microscopy, the fimbriated A. naeslundii and A. viscosus possessed higher cell-surface interactive forces than those nonfimbriated, such as A. bovis, A. gerencseriae, A. israel ii, A. meyeri and A. odontolyticus. When this novel technique was used to quantify cellsurface interactive forces of sessile Actinomyces spp. attached on inert mica substrates, varying force levels were found at different locations of the organism implying complexities associated with bacterial adhesion and coadhesion.
Taken together, the work described indicated that commensal oral Actinomyces spp. play a critical and complex role both in health and disease, together with other putative pathogens sharing the same
Abstract ecological niche. How this genus initially colonizes in the oral cavity,
communicate and co-adhere with other organisms awaits clarification in the further study.
School:The University of Hong Kong
School Location:China - Hong Kong SAR
Source Type:Master's Thesis
Keywords:actinomyces bacteria mouth diseases
Date of Publication:01/01/2004