Spirochetes

1. Spirochetes Prepared by Dr. NajdatB.Mahdi

2. Spirochetes are long, slender, motile, flexible, undulating, gram-negativebacilli that have helical shape. Depending on the species, they can be microaerophilic, aerobic, or anaerobic. Some species can be grown in laboratory culture (either cell free culture or tissueculture), whereas others cannot. Some species are free living, and someare part of the normal flora of humans and animals. Spirochetes that areimportant human pathogens are confined to three genera:Treponema (Treponema pallidum causes syphilis), Borrelia (Borreliaburgdorfericauses Lyme disease and Borreliarecurrentisand Borreliahermsiicause relapsing fever), and Leptospira (Leptospirainterrogans causes leptospirosis).

3. II. STRUCTURAL FEATURES OF SPIROCHETES Spirochetes have a unique structure that is responsible for motility. the spirochete cell has a central protoplasmiccylinder bounded by a plasma membrane and a typical gram-negativecell wall. Unlike in other bacilli, this cylinder is enveloped by an outermembrane composed of glycolipids and lipoproteins1. Between the peptidoglycanand the outer sheath are located multiple periplasmic flagellathat do not protrude from the cell but are oriented axially. Spirochetes can move through highly viscous solutions with littleimpediment, and it is theorized that this kind of motion is responsiblefor the ability of spirochete pathogens to penetrate and invade host tissue, just as a corkscrew penetrates cork

4. TREPONEMA PALLIDUM Syphilis is primarily a sexually transmitted infection caused by the spirocheteT. pallidum. Starting with a small lesion (chancre), several progressivestages of the disease can span a period of 30 years or more,often ending in syphilitic dementia or cardiovascularPrepared by Dr. NajdatB.Mahddamage

5. causative organism of syphilis is extremely fastidious and fragile. It cannotbe cultured in cell-free systems and is sensitive to disinfectants,heat, and drying. T. pallidum is so thin that it cannot be observed byconventional light microscopy but requires immunofluorescent or darkfieldtechniques The outer surface of the spirochete is sparse in proteins, and the organism is only weakly antigenic. T. pallidumsecretes hyaluronidase, an enzyme that disrupts ground substanceand probably facilitates dissemination of the organism. Unliketypical gram-negative bacteria, most spirochetes, including T. pallidum,donot have lipopolysaccharide (LPS), or endotoxin, in the outer leafletof the outer membrane. .

6. Pathogenesis • Transmission of T. pallidum is almost always by sexual contact ortransplacentally (congenital syphilis). This is understandable becausethe organism is so sensitive to environmental factors that survival outsideof the host for more than a few minutes is highly unlikely. Theorganism enters the body through a break in the skin or by penetratingmucous membranes such as those of the genitalia.

7. 1-Syphilis: • Syphilis occurs in three stages . The firstsymptom of primary syphilis is a hard, painless genital or oral • ulcer (chancre) that develops at the site of inoculation. The averageperiod between infection &the appearance of the chancre • is about 3 weeks but varies with thenumber of infecting organisms.

8. Clinical stages of untreated syphilis. CNS = central nervous systems

9. 1. Syphilis This primary lesion heals spontaneously, but the organismcontinues to spread throughout the body via the lymph and blood.An asymptomatic period ensues, lasting as long as 24 weeks, followedby the secondary stage. This stage is characterized by theappearance of a red, maculopapular rash on almost any part ofthe body, including the palms of the hands and soles of the feet Both primary and secondary lesions teemwith T. pallidum and are extremely infectious. The secondary stagemay be accompanied by multiorgan involvement, causing hepatitis,meningitis, nephritis. Upon healing of the secondarylesions, the disease enters a latent period that can last formany years. In approximately 40 percent of infected individualsthe disease progresses to a tertiary stage, characterized by degeneration of the nervous system; cardiovascular lesions, and granulomatous lesions (gummas)in the liver, skin, and bones

10. 2. Congenital syphilis • : T. pallidumcan be transmitted through the placentato a fetus after the first 10 to 15 weeks of pregnancy. Infectioncan cause fetal or infant death or spontaneous abortion. Infectedinfants who live develop a condition similar to secondary syphilis, • including a variety of central nervous system (CNS) and structuralabnormalities. Treatment of the pregnant mother with appropriateantibiotics prevents congenital syphilis

11. Other treponemal infections : Three geographically localized treponemal diseases closely mimic syphilis. They include bejel (found in hot, arid areas of Africa, Southeast Asia, and the Middle East), yaws (found in humid, tropical countries and pinta (found in South and Central America, Mexico, andthe Phillipines). Unlike syphilis, direct skin contact, crowded livingconditions, and poor hygiene contribute to the spread of these diseases.Sexual contact is not usually the mode of transmission, andcongenital infections occur rarely if at all. All three diseases arecurable with penicillin

12. Laboratory identification lesions can be detected microscopically using immunofluorescentstain or dark-field illumination syphilis is usuallydiagnosed serologically. Infection with T. pallidum elicits two kindsof antibodies: 1) antitreponemal antibodies that are specific to the treponemal surface proteins and 2) non treponemal antibodies (reagin),that are directed against normal phospholipid components ofmammalian membranes, such as cardiolipin2. Serologic tests usingboth kinds of antibodies are available. Antitreponemal antibodiestests are more specific than reagin-based tests

13. Treatment and prevention • One single treatment with penicillin is curative for primary and secondarysyphilis, and no antibiotic resistance has been reported. Incases of patient sensitivity to penicillin, alternate therapy with erythromycinor tetracyclines may also be effective There is no vaccine against T. pallidum, & prevention • depends on safe sexual practices. More than one sexually transmitted

14. BORRELIA BURGDORFERI Members of the genus Borrelia are relatively large spirochetes which,like Treponema, have endoflagella that make them highly motile . Borrelia species are unusual among bacteria in that theyhave linear rather than circular plasmid and chromosomal DNA. Like T.pallidum, Borrelia do not produce endotoxin or exotoxins.

15. Lyme disease is caused by the spirochete B.burgdorferi, which istransmitted by the bite of a small tick of the genus Ixodes [Note: The tick must be attached for at least 24 hours before • there is transmission of bacteria. This blood meal results in a heavilyengorged tick.] Mice and other small rodents serve as primary reservoirs • for the spirochete, but deer and other mammals serve as hostsfor the ticks. Lyme disease is currently the most common arthropod transmitted

16. Prepared by Dr. NajdatB.Mahdi