The Genera Prevotella and Porphyromonas

Chapter 38 The Genera Prevotella and Porphyromonas


Prevotella spp. and Porphyromonas spp. are obligately anaerobic, non–spore-forming, nonmotile, pleomorphic rods. Both genera have taxonomic placement in the class Bacteroides, order Bacteroidales; however, Prevotella spp. are members of the family Prevotellaceae, whereas Porphyromonas spp. are classified in Porphyromonadaceae. The species in these genera were formerly included in the genus Bacteroides.


Prevotella spp. are pigmented or nonpigmented asaccharolytic bacteria. Their growth is inhibited by 20% bile, nitrate is not reduced to nitrite, and most are indole negative. More than 20 species inhabit the oral and gastrointestinal cavities of man and other animals. Prevotella spp. comprise one of the largest groups recovered from the rumen and hindgut. They may play an important role in the utilization of plant-origin polysaccharides and in metabolism of proteins and peptides.


Porphyromonads may be pigmented or nonpigmented and are asaccharolytic to weakly saccharolytic. Indole is produced and nitrate is not reduced to nitrite. Generic taxonomy is evolving rapidly, with 13 currently recognized species. Porphyromonas spp. are found primarily in the oral cavity of man and animals.



DISEASE AND EPIDEMIOLOGY


Prevotella melaninogenica (Bacteroides melaninogenicus), so named because of its colonial pigment, is isolated (in pure or mixed culture) from suppurative lesions in a variety of animals. It is frequently associated with Fusobacterium necrophorum and Arcanobacterium pyogenes in bovine footrot. Prevotella melaninogenica is a common isolate from various lesions in dogs and cats, and is often involved in life-threatening infections. Prevotella intermedia and Prevotella nigrescens cause abscesses, naturally and experimentally, often (in the former case) in company with facultative anaerobes or aerobes.


The normal oral residence of many Prevotella spp. is reflected in their common isolation from dog- and cat-bite wounds, perhaps explaining in part their frequent recovery from various soft tissue infections in cats and dogs. Prevotella heparinolytica is common and Prevotella zoogleoformans and Prevotella oralis are occasional in such lesions.


Prevotella melaninogenica is not uncommon as a cause of acute tonsillitis in children, and subcutaneous inoculation of mice with strains recovered from these lesions produces abscesses, whereas this is seldom the case with isolates from the normal respiratory mucosa. Sputum IgA titers against Prevotella intermedia are significantly elevated in humans with acute exacerbation of chronic bronchitis.


Prevotella spp. are also found in lower respiratory tract disease in horses, again frequently in company with facultative anaerobes. Significant numbers of anaerobic bacteria are isolated only after the fifth day of illness. Pleural fluid from these animals is usually culture negative, but transtracheal aspirates and lung tissues collected at necropsy frequently yield Prevotella heparinolytica and pigmented Prevotella spp. as well as Porphyromonas spp. Isolation of pulmonary anaerobes from horses augurs against recovery.


Porphyromonas gingivalis causes marked lung inflammation in humans, and this condition can progress to severe bronchopneumonia with lung abscesses. This organism originates in the oral cavity, and is a significant cause of human aspiration pneumonia and lung abscess. The mortality rate is 25% in mice inoculated intratracheally with P. gingivalis. Surviving animals evidence a marked recruitment of neutrophils, with substantial reduction in bacterial populations within 48 hours. Despite this, mice develop acute necrotizing bronchopneumonia, often with abscessation. Increased lactate dehydrogenase (LDH) in pulmonary lavage fluids suggests severe parenchymal damage, and extensive influx of serum albumin is compatible with injury to alveolar capillary membranes.


On the whole, Prevotella spp. are less invasive than Fusobacterium spp., and are seldom found other than transiently in the bloodstream. Prevotella spp. and Porphyromonas spp. are among the most common microorganisms isolated from human tubo-ovarian abscesses, and pigmented members of these genera are predominant among anaerobes causing infection and inflammation of the parotid salivary gland.


Porphyromonas levii is a common cause of summer mastitis in cattle, ranking third behind F. necrophorum and Peptostreptococcus indolicus among the anaerobes. Isolates of P. levii are common on conjunctivae and teat tips among clinically healthy animals, suggesting that contributing factors are required for development of clinical disease. Incidence is significantly higher during the pasture period, and the distinctly seasonal distribution coincides with seasonal activity of symbovine insects, such as headflies (Hydrotaea irritans). Porphyromonas levii is also isolated in conjunction with Actinomyces spp. from pleural effusions in dogs and in conjunction with fusobacteria from bovine and ovine footrot.


Porphyromonas gingivalis, as well as P. intermedia, are involved in the onset of periodontal disease in humans and domestic animals. Porphyromonas gingivalis is common in active periodontitis sites, and patients with periodontitis have higher antibody titers against it. Prevotella intermedia is frequently isolated from subgingival sites in periodontitis and various forms of gingivitis. It also is found in dental crevices of periodontally healthy subjects. Many new species have been described recently. Porphyromonas cangingivalis, Porphyromonas cansulci, Porphyromonas gingivicanis, Porphyromonas creviorcanis, Porphyromonas canoris, and Porphyromonas gulae have been associated with periodontitis in animals.


Prevotella nigrescens, a close relative of P. intermedia, seems to be associated with endodontic infection and adult gingivitis, whereas P. intermedia is more common in periodontal lesions.


Odontogenic mandibular and maxillary abscesses in domestic rabbits are consistent, in bacteriologic characteristics, with periodontal disease in humans, although they are typically caused by Prevotella heparinolytica and other Prevotella spp. not ordinarily involved in human disease.


Animal strains (from the oral cavities of cats, dogs, and other carnivores) resolve into a biotype of P. gingivalis that is different from the biotype containing human strains. Feline P. gingivalis is 75% DNA homologous with human P. gingivalis, and is one of multiple species of porphyromonads isolated from the feline oral cavity and oral-associated disease. Porphyromonas macacae biotype salivosa and Porphyromonas circumdentaria also are found occasionally.


Domestic sheep develop a form of periodontitis called “broken-mouth,” characterized by premature spontaneous exfoliation of teeth and accompanied by malnutrition, weight loss, and systemic health problems. Oral microbes in periodontally diseased sheep are consistent with findings from humans with periodontitis. Affected animals yield cultures of P. gingivalis and P. intermedia, and elevated serum IgG titers to these organisms vary directly with the number of teeth lost and decreases in body weight.


There may be an association between periodontal disease and cardiovascular disease in humans. Hematogenous dissemination from chronic subgingival periodontal infections may infect vascular endothelium, contributing to atherosclerosis and increasing the risk of myocardial ischemia and infarction. Porphyromonas gingivalis causes platelet aggregation in vitro, suggesting a contribution to thrombotic effects in vivo. Results of experimental studies in animals suggest that atheromagenesis is amplified in the presence of periodontal pathogens. Polymerase chain reaction (PCR) examination of atherosclerotic plaque has revealed P. gingivalis.

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Jul 18, 2016 | Posted by in PHARMACOLOGY, TOXICOLOGY & THERAPEUTICS | Comments Off on The Genera Prevotella and Porphyromonas

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