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Spirochaetes are a diverse group of spiral, motile organisms comprising five genera. Of these, three genera are human pathogens:

• causes , bejel, , and, in the oral cavity, acute necrotizing ulcerative gingivitis (together with )

• causes and

• causes .

Spirochaetes are helical organisms with a central protoplasmic cylinder surrounded by a cytoplasmic membrane

• The cell wall is similar to Gram-negative but stains poorly with the Gram stain. Underneath the cell wall run three to five axial filaments that are fixed to the extremi- ties of the organism. Contractions of these filaments distort the bacterial cell body to give it its helical shape. The organism moves either by rotation along the long axis or by flexion of cells. Because of their weak refractile nature, dark-ground microscopy is used to visualize these organisms in the laboratory, although immunofluorescence is more useful for 3 Microbes of relevance to dentistry identification purposes. All spirochaetes are strictly anaerobic or microaerophilic microaerophilic.

Axial Outer cell filaments Protoplasmic envelope cylinder

A B C

Borrelia Treponema Leptospira Fig. 18.3 Structure of a (top) and the morphology of the three Fig. 1- Structuremajor genera of of a spirochaetes.spirochaete (top) and the morphology of the three major genera of spirochaetes. Fig. 18.1 A photomicrograph of fusobacteria showing characteristic Gram-negative, cigar-shaped cells with pointed ends.

18.3). The cell wall is similar to Gram-negative bacteria but stains poorly with the Gram stain. Underneath the cell wall run three to five axial filaments that are fixed to the extremi- ties of the organism. Contractions of these filaments distort 1 the bacterial cell body to give it its helical shape. The organ- ism moves either by rotation along the long axis or by flexion of cells. Because of their weak refractile nature, dark-ground microscopy is used to visualize these organisms in the labo- ratory, although immunofluorescence is more useful for identification purposes. All spirochaetes are strictly anaero- bic or microaerophilic.

Treponema

The coils of Treponema are regular, with a longer wavelength Fig. 18.2 A Gram-stained smear obtained from deep gingival plaque of a than that of Leptospira (Fig. 18.3). A number of species and patient with acute ulcerative gingivitis (see also Fig. 33.6) showing the subspecies are recognized, some of which are important sys- fusospirochaetal complex. Note: the large cells are polymorphs. temic pathogens, while others are oral inhabitants impli- cated in periodontal disease. proportions in dental plaque, is the sole representative of this genus. Habitat and transmission Spirochaetes Lesions of primary and secondary syphilis Transmission is by direct contact with lesions, body secre- Spirochaetes are a diverse group of spiral, motile organisms tions, blood, semen and saliva, usually during sexual contact, comprising five genera. Of these, three genera are human and from mother to foetus by placental transfer. pathogens: • Treponema causes syphilis, bejel, yaws, pinta and, in the Characteristics oral cavity, acute necrotizing ulcerative gingivitis Slender, corkscrew-shaped cells with 6–12 evenly spaced (together with fusobacteria) coils, 6–14 × 0.2 μm; too slender to visualize by light micro- Borrelia causes relapsing fever and Lyme disease • scopy but can be seen by silver impregnation or immuno- Leptospira causes leptospirosis. • fluorescent techniques; strictly anaerobic and extremely Spirochaetes are helical organisms with a central protoplas- sensitive to drying and heat, hence dies rapidly outside mic cylinder surrounded by a cytoplasmic membrane (Fig. the body.

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Treponema

The coils of Treponema are regular, with a longer wavelength than that of Leptospira (Fig. 1). A number of species and subspecies are recognized, some of which are important systemic pathogens, while others are oral inhabitants implicated in periodontal disease.

Treponema pallidum

Habitat and transmission

Lesions of primary and secondary syphilis

Transmission is by direct contact with lesions, body secretions, blood, semen and saliva, usually during sexual contact, and from mother to fetus by placental transfer.

Characteristics

Slender, corkscrew-shaped cells with 6–12 evenly spaced coils, 6–14 × 0.2 µm; too slender to visualize by light microscopy but can be seen by silver impregnation or immunofluorescent techniques; strictly anaerobic and extremely sensitive to drying and heat, hence dies rapidly outside the body.

Culture and identification

Cannot be cultured in vitro, but can be propagated in the testes of rabbits; Treponema pallidum thus harvested can be used as antigens to detect specific antibody in the patient’s serum.

Dark-ground microscopy of tissue fluid from primary and secondary clinical lesions helps identification, but serological tests are the mainstay of diagnosis.

Pathogenicity

Causes syphilis, a sexually transmitted disease with protean manifestations. The virulence factors of T. pallidum are not well characterized. Immunopathology plays a significant role in disease manifestations, especially in the late (tertiary and quaternary) stages of the disease.

Antibiotic sensitivity and control

Penicillin is the drug of choice; for allergic patients, tetracycline is an alternative. Prevention of

2 syphilis is based on early detection, contact tracing and serological testing of pregnant women.

Treponema pallidum subsp. pertenue

The agent of yaws, characterized by chronic, ulcerative, granulomatous lesions of skin, mucosae and bone. The disease, widespread in the tropics, is spread by direct contact.

Treponema carateum

The agent of pinta, a non-venereal skin infection characterized by depigmented and hyperkeratotic skin. The disease affects mainly dark-skinned natives of Central and South America and the West Indies.

Oral treponemes

All oral spirochaetes are classified in the genus Treponema. Although many species have been described, only four have been cultivated and maintained reliably: , Treponema vincentii, Treponema pectinovarum and Treponema socranskii. In another classification, they are cate- gorized according to cell size as small, medium and large spirochaetes.

Habitat and transmission

Predominantly, the oral cavity of humans and primates, at the gingival margin and crevice in particular. Transmission routes are unknown. Infections are endogenous.

Characteristics

Motile, helical rods, 5–15 × 0.5 µm, with irregular (three to eight) spirals, which are less tightly coiled than, for instance, T. pallidum (Fig1&Fig-2). Cell walls are Gram-negative but stain poorly. The3 Microbes size of relevance isto dentistry variable and can be used as a basis for classification (large, medium or small).

Fig. 18.4 Scanning electron micrograph of the radicular surface of a tooth affected by advanced periodontal disease showing the spirochaetes on the root surface.

LeptospiraFig. 2- Scanning electron micrographand domestic animals act asof a reservoir the for radicular L. interrogans. surface of a tooth affected by advanced periodontal The urine of these animals serves as a vehicle of transmission of human leptospirosis, the symptoms of which vary from Leptospiradisease biflexa and showing theare the recognizedspirochaetes on the root surface. mild febrile illness to fatal attacks of jaundice and renal species, each of which comprises a number of serogroups. failure. These organisms are found in damp environments such as stagnant water and wet soil. The kidneys of some rodents

KEY FACTS

• Fusobacteria are non-sporing, anaerobic, spindle-shaped bacilli • Spirochaetes comprise three genera: Treponema, Borrelia and inhabiting the oral cavity, colon and female genital tract. Leptospira. 3 • The type species and Fusobacterium • Treponema pallidum, the agent of syphilis, cannot be cultivated in periodonticum are isolated mainly from periodontal disease sites vitro and is uniformly sensitive to penicillin. and hence considered to be periodontopathic bacteria. • All oral spirochaetes are classified in the genus Treponema (type • Fusospirochaetal infections caused by fusobacteria in combination strain Treponema denticola). with spirochaetes are acute ulcerative gingivitis, Vincent’s angina • T. denticola is a coagent of fusospirochaetal infection and and cancrum oris (or ). advanced periodontal disease. • Spirochaetes are long, slender, coiled and highly mobile bacteria • T. denticola, and are that do not take up the Gram stain. considered the three agents of red complex bacteria almost always associated with periodontal disease.

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Culture and identification

In contrast to T. pallidum, oral spirochaetes can be grown in vitro. They are strict anaerobes, slow- growing in oral treponema isolation (OTI) medium. Subspecies can be differentiated by fermentation reactions and serology (agglutination).

Suspect lesions of acute necrotizing ulcerative gingivitis or advanced periodontitis can be examined by obtaining a Gram-stained smear of deep gingival plaque and visualizing the characteristic fusospirochaetal complex under light microscopy; alternatively, dark-ground micro scopy may be used.

Pathogenicity

These organisms are a component of the fusospirochaetal complex of acute necrotizing ulcerative gingivitis and Vincent’s angina, and are a coagent of advanced periodontal disease. The ability to travel through viscous environments enables oral spirochaetes to migrate within the gingival crevicular fluid and to penetrate sulcular epithelial linings as well as gingival connective tissue. Virulence factors are little known; endotoxin is possibly contributory to disease. T. denticola is more proteolytic than other species and degrades collagen and dentine.

Antibiotic sensitivity and control

Sensitive to penicillin and metronidazole. Prevention of infection is achieved by good oral hygiene practices.

BOOK: Essential microbiology for dentistry 2012. Elsevier Ltd. Fourth edition, Lakshman Samaranayake. Elsevier Ltd.

Prepared by Assist. Prof. Dr. Zainab Khudhur Ahmad Al-Mahdi

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