Pigmented-anaerobic bacteria associated with canine periodontitis

Abstract

The etiology of human periodontal disease has been the focus of considerable research, yet relatively little is known about the causative agents of companion animal periodontitis. In humans, Porphyromonas gingivalis, a black-pigmented anaerobic bacteria (BPAB), has been implicated as the primary periopathogen. It has been demonstrated that BPAB are also found in companion animal periodontal pockets. While some animal BPAB have been individually identified, a study to identify the most frequently isolated subgingival BPAB has not been completed using genetic tools. The objective of this work was to identify the types and relative frequencies of pigmented anaerobic bacteria found in the periodontal pockets of dogs. Porphyromonas salivosa, Porphyromonas denticanis (a novel species) and Porphyromonas gulae were found to be the most frequently isolated BPAB associated with canine periodontitis.

Introduction

Periodontal disease is a chronic, multi-factorial disease of the tissues supporting the teeth (Loesche and Grossman, 2001, Page and Houston, 1999). Both host and bacterial factors influence the course of disease. Much of the published data regarding the etiology of periodontitis comes from research on human disease. The primary periodontal pathogen in humans is P. gingivalis (Cutler et al., 1995, Lamont and Jenkinson, 1998, Page, 2000, Page and Houston, 1999). This organism appears to be transmitted by infected individuals and to colonize naïve individuals at a young age (Lamont and Jenkinson, 1998, Yang et al., 2002). The population of P. gingivalis begins to increase as an anaerobic environment is generated due to the oxygen scavenging activity of early subgingival colonizers and the effect of early oral diseases such as gingivitis. Once firmly established, the virulence factors expressed by P. gingivalis can take effect and lead to active disease (Cutler et al., 1995, Genco et al., 1999, Lamont and Jenkinson, 1998).

Periodontitis in companion animals is an almost identical disease to that in humans in terms of disease course and clinical presentation. It has been estimated that approximately 80% of dogs and cats demonstrate some degree of periodontal disease by 4 years of age (Harvey and Emily, 1993, Penman and Harvey, 1990). The accelerated disease progression observed in companion animals compared to humans may be due to a relative lack of routine dental care. By age five, the percentage of Porphyromonas spp. isolated from canine plaque is roughly six-fold higher than at 2 years of age, and correlates with disease severity (Allaker et al., 1997a; Isogai et al., 1999). Companion animal periodontitis is a serious infection that can have medical consequences such as anorexia and weight loss, chronic pain, sore or loose teeth, swollen gums, tooth decay, breakage or loss of teeth, and breakage of the maxillary or mandibular bone. If left untreated, periodontal bacteria may spread to other sites in the body and lead to renal, coronary, or hepatic diseases (DeBowes et al., 1996, Okuda et al., 2004, Scannapieco et al., 2003).

While the etiology of human periodontal disease has received much attention, there is a paucity of information available about the etiology of companion animal periodontitis. Black pigmenting anaerobic bacteria (BPAB) have been isolated from the periodontal pockets of dogs and cats (Allaker et al., 1997a; Boyce et al., 1995, Forsblom et al., 1997, Harvey et al., 1995, Harvey, 1998, Hennet and Harvey, 1991, Isogai et al., 1999), sheep (Dreyer and Basson, 1992, Duncan et al., 2003), and several wild animals (Fournier et al., 2001). Many of these isolates appear to be Porphyromonas spp. (Allaker et al., 1997a; Isogai et al., 1999). However, several differences between human and companion animal Porphyromonas isolates have been reported. Most notably, “human” P. gingivalis isolates are catalase-negative whereas, “veterinary” P. gingivalis isolates are catalase-positive (Harvey et al., 1995, Isogai et al., 1999). These catalase-positive P. gingivalis-like organisms may well represent isolates of Porphyromonas gulae (Fournier et al., 2001). In addition to the P. gingivalis-like organisms, other Porphyromonas spp. have been identified from companion animal periodontal pocket samples (Porphyromonas canoris, Porphyromonas cangingivalis, Porphyromonas canis, Porphyromonas cansulci, P. gingivicanis, and Porphyromonas crevioricanis) (Collins et al., 1994, Fournier et al., 2001, Hirasawa and Takada, 1994, Love et al., 1994).

To identify the relative frequencies of BPAB in companion animal periodontal disease, we conducted a study in dogs in which BPAB were isolated from the crevicular spaces of dogs with active periodontitis. The resulting bacterial isolates were genetically typed by 16S ribosomal RNA DNA sequence analysis. The three most frequently isolated BPAB were Porphyromonas salivosa, Porphyromonas denticanis (a new bacterial species), and P. gulae.