Spirochetes, Mycoplasmataceae, Chlamydiales - Microbiology PDF

SPIROCHETES, MYCOPLASMATACEAE, CHLAMYDIALES BEDİA DİNÇ  Three genera of spirochetes cause human infection Treponema, which causes syphilis and the nonvenereal treponematoses; Borrelia, which causes Lyme disease and relapsing fever; Leptospira, which causes leptospirosis. ...

SPIROCHETES, MYCOPLASMATACEAE, CHLAMYDIALES BEDİA DİNÇ  Three genera of spirochetes cause human infection Treponema, which causes syphilis and the nonvenereal treponematoses; Borrelia, which causes Lyme disease and relapsing fever; Leptospira, which causes leptospirosis.  Spirochetes are thin-walled, flexible, spiral rods Motile through the undulation of axial filaments that lie under the outer sheath. Treponema and leptospirae are so thin that they are seen only by dark-field microscopy, silver impregnation, or immunofluorescence. Borreliae are larger, accept Giemsa and other blood stains, and can be seen in the Standard light microscope. TREPONEMA - T.pallidum Causes syphilis. Has not been grown on bacteriologic media or in cell culture but nonpathogenic treponemes, which are part of the normal flora of human mucous membranes, can be cultured. T. pallidum grows very slowly, so antibiotics must be present at an effective level for several weeks to kill the organisms and cure the disease The antigens of T. pallidum induce specific antibodies, which can be detected by immunofluorescence or hemagglutination tests in the clinical laboratory. They also induce nonspecific antibodies (reagin), which can be detected by the flocculation of lipids (cardiolipin) extracted from normal mammalian tissues. Both specific antitreponemal antibody and nonspecific reagin are used in the serologic diagnosis of syphilis. Transmission & Epidemiology Transmitted from spirochete-containing lesions of skin or mucous membranes (e.g., genitalia, mouth, and anus) of an infected person to other persons by intimate contact. Also can be transmitted from pregnant women to their fetuses. Rarely, blood for transfusions collected during early syphilis is also infectious. Syphilis occurs worldwide with an increasing incidence especially among men who have sex with men in recent years Pathogenesis & Clinical Findings Produces no important toxins or enzymes. Often infects the endothelium of small blood vessels, causing endarteritis which occurs during all stages of syphilis but is particularly important in the pathogenesis of the brain and cardiovascular lesions seen in tertiary syphilis. In primary syphilis, the spirochetes multiply at the site of inoculation, and a local, nontender ulcer (chancre) usually forms in 2 to 10 weeks. The ulcer heals spontaneously, but spirochetes spread widely via the bloodstream (bacteremia) to many organs.  One to three months later, the lesions of secondary syphilis may occur. These lesions often appear as a maculopapular rash, notably on the palms and soles, or as moist papules on skin and mucous membranes (mucous patches). Moist lesions on the genitals are called condylomata lata. These lesions are rich in spirochetes and are highly infectious, but they also heal spontaneously. Patchy alopecia also occurs. Constitutional symptoms of secondary syphilis include low-grade fever, malaise, anorexia, weight loss, headache, myalgias, and generalized lymphadenopathy. Pharyngitis, meningitis, nephritis, and hepatitis may also occur. About one-third of these early (primary and secondary) syphilis cases will “cure” themselves, without treatment. Another third remain latent (i.e., no lesions appear, but positive serologic tests indicate continuing infection).  The latent period; early and late stages. Early latent period, can last for 1 or 2 years after the secondary stage, the symptoms of secondary syphilis can reappear and patients can infect others. Late latent period, can last for many years, no symptoms occur and patients are not infectious. In the remaining one-third of people, the disease progresses to the tertiary stage. Tertiary syphilis may show granulomas (gummas), especially of skin and bones; Central nervous system involvement, also known as neurosyphilis or cardiovascular lesions In tertiary lesions, treponemes are rarely seen.  Also causes congenital syphilis by transmission across the placenta, typically after the third month of pregnancy. In the infected neonates, skin and bone lesions, such as Hutchinsons teeth, mulberry molars, saber shins, saddle nose, rhagades, snuffles, and frontal bossing, are common. Other findings, such as hepatosplenomegaly, interstitial keratitis, and eighth nerve deafness, also occur. Fetal infection can also result in stillbirth. !!All pregnant women should be tested for syphilis at least twice during pregnancy. Laboratory Diagnosis Microscopy; Spirochetes are demonstrated in the lesions of primary or secondary syphilis, such as chancres or condylomata lata, by dark-field microscopy or by direct fluorescent antibody (DFA) test. They are not seen on a Gram-stained smear. In biopsy specimens, such as those obtained from the gummas seen in tertiary syphilis, histologic stains such as silver stain or fluorescent antibody can be used.  Nonspecific Serologic Tests; involve the use of nontreponemal antigens. Extracts of normal mammalian tissues (e.g., cardiolipin from beef heart) react with antibodies in serum samples from patients with syphilis. These antibodies, which are a mixture of IgG and IgM, are called “reagin” antibodies. Flocculation tests (e.g., Venereal Disease Research Laboratory [VDRL] rapid plasma reagin [RPR] tests detect the presence of these antibodies. These tests are positive in most cases of primary syphilis and are almost always positive in secondary syphilis. The titer of these nonspecific antibodies decreases with effective treatment, in contrast to the specific antibodies, which are positive for life.  !!!Positive results have to be confirmed by specific tests. Results of nonspecific tests usually become negative after treatment and should be used to determine the response to treatment. Inexpensive and easy to perform and used as screening method. The laboratory diagnosis of congenital syphilis is based on the finding that the infant has a higher titer of antibody in the VDRL test than the mother.  Specific Serologic Tests; involve the use of treponemal antigens and therefore are more specific than nonspecific tests. T. pallidum reacts in immunofluorescence (FTA-ABS) or hemagglutination (TPHA, MHA-TP) assays with specific treponemal antibodies in the patient’s serum. The Treponema pallidum particle agglutination test (TPPA) is also used. These antibodies arise within 2 to 3 weeks of infection; therefore, the test results are positive in most patients with primary syphilis. Remain positive for life after effective treatment and cannot be used to determine the response to treatment or reinfection. More expensive and more difficult to perform than the nonspecific tests and therefore are not used as screening procedures.  Treatment; Penicillin G; effective in the treatment of all stages of syphilis. Pregnant women with syphilis should be treated promptly with the type of penicillin used for the stage of their disease. Neonates with a positive seroiogic test should also be treated. More than half of patients with secondary syphilis who are treated with penicillin experience fever, chills, myalgias, and other influenza like symptoms a few hours after receiving the antibiotic (Jarisch-Herxheimer reaction; attributed to the lysis of the treponemes and the release of endotoxin-like substances).  Prevention; early diagnosis and adequate treatment, use of condoms, administration of antibiotic after suspected exposure, and serologic follow-up of infected individuals and their contacts. To prevent congenital syphilis, all pregnant women should be screened by using a treponemal test such as FTA-ABS. No vaccine.  Nonvenereal Treponematoses Infections caused by spirochetes that are virtually indistinguishable from those caused by T. pallidum. Endemic in populations and are transmitted by direct contact. All these infections result in positive (nontreponemal and treponemal) results on serologic tests for syphilis. None of these spirochetes have been grown on bacteriologic media. The diseases include bejel in Africa, yaws (caused by T.pallidum subspecies pertenue) in many humid tropical countries, and pinta (caused by Treponema carateum) in Central and South America. All can be cured by penicillin. BORRELIA Irregular, loosely coiled spirochetes that stain readily with Giemsa and other stains. Can be cultured in bacteriologic media containing serum or tissue extracts. Transmitted by arthropods. Cause two major diseases; Lyme disease Relapsing fever. Borrelia burgdorferi Causes Lyme disease also known as Lyme borreliosis. The most common tick-borne disease in the United States.  Flexible, motile spirochete that can be visualized by dark-field microscopy and by Giemsa and silver stains. Can be grown in certain bacteriologic media, but routine cultures obtained from patients (e.g., blood, spinal fluid) are typically negative. In contrast, culture of the organism from the tick vector is usually positive. Transmitted by tick bite. The main reservoir of the organism consists of small mammals, especially the white-footed mouse, upon which the nymphs feed. Large mammals, especially deer, are an obligatory host in the tick’s life cycle but are not an important reservoir of the organism. The nymphal stage of the tick transmits the disease more often than the adult and larval stages do. Nymphs feed primarily in the summer, which accounts for the high incidence of disease during the months of May to September. The tick must feed for 24 to 48 hours to transmit an infectious dose. There is no human-to-human spread.  Occurs worldwide. Pathogenesis is associated with spread of the organism from the bite site through the surrounding skin followed by dissemination via the blood (bacteremia) to various organs, especially the heart, joints and Central nervous system. No exotoxins, enzymes, or other important virulence factors  Clinical Findings Three stages; Stage 1 (early localized stage); the most common finding is erythema chronicum migrans (also called erythema migrans); an expanding, erythematous, macular rash that often has a “target” or “bull’s eye” appearance which appears between 3 and 30 days after the tick bite. Both the tick bite and the rash are painless and nonpruritic. The rash may be accompanied by nonspecific “flulike” symptoms such as fever, chills, fatigue, myalgia, and headache. Secondary skin lesions frequently occur. Arthralgias, but not arthritis, are another common finding in this early stage.  In stage 2 (early disseminated stage); occurs weeks to months later, cardiac and neurologic involvement predominates. Myocarditis, accompanied by various forms of heart block Acute (aseptic) meningitis and cranial neuropathies, such as facial nerve palsy (Bell’s palsy) Bilateral facial nerve palsy is highly suggestive of Lyme disease. Peripheral neuropathies also occur. A latent phase lasting weeks to months typically ensues.  In stage 3 (late disseminated stage), arthritis, usually of the large joints Lyme arthritis is thought to be autoimmune in origin. Encephalopathy  Laboratory Diagnosis Cultures; rarely positive and are usually not performed. Serologically by detecting either IgM antibody or a rising titer of IgG antibody with an enzyme-linked immunosorbent assay (ELISA). A positive test result should be confirmed with a Western blot (immunoblot) analysis. Patients treated early in the disease may not develop detectable antibodies. PCR assays. Treatment & Prevention Doxycycline or amoxicillin; stage 1 disease or other mild manifestations. Ceftriaxone; more severe forms or late-stage disease Prevention; wearing protective clothing and using insect repellents, examining the skin carefully for ticks, because the tick must feed for 24 to 48 hours to transmit an infective dose. Any person bitten by a tick should be advised to watch carefully for a rash or flulike symptoms for the next 3 weeks. A vaccine containing recombinant outer surface protein A (OspA) of B.burgdorferi as the immunogen was available but has been withdrawn.  Borrelia recurrentis & Borrelia hermsii Borrelia recurrentis & Borrelia hermsii and several other borreliae cause relapsing fever. B.recurrentis; transmitted from person to person by the human body louse. B. hermsii and many other Borrelia species; transmitted by soft ticks (Ornithodoros). During infection, the arthropod bite introduces spirochetes, which then multiply in many tissues, producing fever, chills, headaches, and multiple-organ dysfunction. Diagnosis; the large spirochetes in stained smears of peripheral blood. Can be cultured in special media, serologic tests are rarely useful. Tetracycline Prevention; avoidance of arthropod vectors Borrelia miyamotoi Causes a relapsing fever like syndrome. Seen worldwide Transmitted by Ixodes ticks. Clinically; begins with an influenza like syndrome (fever, headache, and myalgia) accompanied by hepatitis and thrombocytopenia. Relapsing episodes occur. There is no rash, unlike Lyme disease. Diagnosis; detecting IgM antibody or by PCR assay Treatment; doxy cycline and ceftriaxone No vaccine. Prevention; wearing clothing impregnated with Permethrin to reduce the risk of tick bites. LEPTOSPIRA Tightly coiled spirochetes with hooked ends. Stain poorly with dyes and so are not seen by light microscopy, seen by dark-field microscopy. Grow in bacteriologic media containing serum. Leptospirosis is common in tropical countries, especially in the rainy season. Leptospira interrogans The cause of leptospirosis.. Leptospiras infect various animals, including rats and other rodents, domestic livestock, and household pets. Animals excrete leptospiras in urine, which contaminates water and soil. Swimming in contaminated water or consuming contaminated food or drink can result in human infection. Outbreaks have occurred among participants in triathlons and adventure tours involving swimming in contaminated waters. Miners, farmers, and people who work in sewers are at high risk. Person-to-person transmission is rare.  Human infection results when leptospiras are ingested or pass through mucous membranes or skin. They circulate in the blood and multiply in various organs, producing fever and dysfunction of the liver (jaundice), kidneys (uremia), lungs (hemorrhage), and Central nervous system (aseptic meningitis). The illness is typically biphasic, with fever, chills, intense headache, and conjunctival suffusion (diffuse reddening of the conjunctivae) appearing early in the disease, followed by a short period of resolution of these symptoms as the organisms are cleared from the blood. The second, “immune,” phase is most often characterized by the findings of aseptic meningitis and, in severe cases, liver damage (jaundice) and impaired kidney function. Diagnosis; based on history of possible exposure, suggestive clinical signs, and a marked rise in IgM antibody titers. Occasionally, leptospiras are isolated from blood and urine cultures. Penicillin G. Prevention; avoiding contact with the contaminated environment. Doxycycline is effective in preventing the disease in exposed persons. Mycoplasmas A group of very small, wall-less organisms, of which Mycoplasma pneumoniae is the major pathogen. M. pneumoniae causes “atypical” pneumonia Most striking feature; the absence of a cell wall!! (stain poorly with Gram stain, and antibiotics that inhibit cell wall (peptidoglycan) synthesis (e.g., penicillins and cephalosporins) are ineffective). Can be grown in the laboratory on artifıcial media, but they have complex nutritional requirements, including several lipids. They grow slowly and require at least 1 week to form a visible colony. The colony frequently has a characteristic “fried-egg” shape.  Transmitted by respiratory droplets. Occurs worldwide, with an increased incidence in the winter. The most common cause of pneumonia in young adults and is responsible for outbreaks in groups with close contacts such as families, military personnel, and college students  Clinical Findings Atypical pneumonia. Atypical; a causative bacterium cannot be isolated on routine media in the diagnostic laboratory or that the disease does not resemble pneumococcal pneumonia. Usually begins with a nonproductive cough, sore throat, or earache. Small amounts of whitish, nonbloody sputum are produced. Constitutional symptoms of fever, headache, malaise, and myalgias Resolves spontaneously in 10 to 14 days. In addition, M. pneumoniae also causes bronchitis. The extrapulmonary manifestations include Stevens-Johnson syndrome, erythema multiforme, mucositis, Raynaud’s phenomenon, cardiac arrhythmias, arthralgias, hemolytic anemia, and neurologic manifestations such as encephalitis and Guillain- Barre syndrome. Laboratory Diagnosis& Treatment It takes at least 1 week for colonies to appear on special media, not useful. PCR assays Serologic testing. The diagnosis of M. pneumoniae infection can be confirmed by a fourfold or greater rise in specific antibody titer in either a complement fixation or an enzyme-linked immunosorbent assay (ELISA) test. Treatment; either a macrolide, such as erythromycin or azithromycin, or a tetracycline, such as doxycycline; shorten the duration of symptoms, althoughthe disease resolves spontaneously. Penicillins and cephalosporins are inactive because the organism has no cell wall. Mycoplasma hominis& Mycoplasma genitalium& Ureaplasma urealyticum Mycoplasma hominis; implicated as an infrequent cause of pelvic inflammatory disease. Mycoplasma genitalium; urethritis, predominantly in men. It is estimated to cause approximately 20% of nongonococcal urethritis (NGU). Infections in women are typically asymptomatic but cervicitis may occur. PCR Azithromycin Ureaplasma urealyticum may cause approximately 20% of cases of NGU. Ureaplasmas can be distinguished from mycoplasmas by their ability to produce urease Azithromycin to treat symptomatic infections. Chlamydiae Chlamydia trachomatis Chlamydia pneumoniae Chlamydia psittaci Obligate intracellular bacteria, they can grow only within cells Cause urethritis and cervicitis, as well as other infections, such as pneumonia, psittacosis, trachoma, and lymphogranuloma venereum.  Chlamydia trachomatis Chlamydia trachomatis causes eye (conjunctivitis, trachoma), respiratory (pneumonia), and genital tract (urethritis, lymphogranuloma venereum) infections. Infection with C. trachomatis is also associated with Reiter’s syndrome, an autoimmune disease. Approximately 40% of nongonococcal urethritis is caused by C. trachomatis. Chlamydia pneumoniae causes atypical pneumonia. Chlamydia psittaci causes psittacosis, also a disease characterized mainly by pneumonia C. pneumoniae and C. psittaci are sufficiently different molecularly from C. trachomatis that they have been reclassified into a new genus called Chlamydophila.  Chlamydiae; obligate intracellular bacteria which lack the ability to produce sufficient energy to grow independently and therefore can grow only inside host cells. Their cell walls resemble those of gram- negative bacteria but lack muramic acid. Chlamydiae have a replicative cycle different from that of all other bacteria. The cycle begins when the extracellular, metabolically inert, “sporelike” elementary body enters the cell and reorganizes into a larger, metabolically active reticulate body. Reticulate body undergoes repeated cycles of binary fission to form daughter reticulate bodies, which then develop into elementary bodies, which are released from the cell. Within cells, the site of replication appears as an inclusion body in the cytoplasm, which  Transmission & Epidemiology C. trachomatis infects only humans and is usually transmitted by close personal contact (e.g., sexually or by passage through the birth canal). Individuals with asymptomatic genital tract infections are an important reservoir of infection for others. In trachoma, C. trachomatis is transmitted by finger-to-eye or fomite-to- eye contact. C. pneumoniae infects only humans and is transmitted from person to person by aerosol. C. psittaci infects birds (e.g., parrots, pigeons, and poultry, and many mammals including humans). Humans are infected primarily by inhaling organisms in airborne dry bird feces.  CHLAMYDIA TRACHOMATIS Has more than 15 immunotypes (A-L). Types A, B, and C cause trachoma, a chronic conjunctivitis endemic in Africa and Asia which may lead to blindness but causes no systemic illness. Types D -K cause genital tract infections. Asymptomatic infections are very common in both men and women. Infants born to infected mothers often develop mucopurulent conjunctivitis (neonatal inclusion conjunctivitis) 7 to 12 days after delivery, and some develop chlamydial pneumonia 2 to 12 weeks after birth. Chlamydial conjunctivitis also occurs in adults as a result of the transfer of organisms from the genitals to the eye. C. trachomatis L1-L3 immunotypes cause lymphogranuloma venereum, a sexually transmitted disease with lesions on genitalia and in lymph nodes. CHLAMYDIA PNEUMONIAE Causes upper and lower respiratory tract infections, especially bronchitis and pneumonia, in young adults. Most infections are mild or asymptomatic. The clinical picture resembles other atypical pneumonias, especially that caused by Mycoplasma pneumoniae. It is unclear whether C. pneumoniae causes upper respiratory infections such as sinusitis and otitis media. CHLAMYDIA PSITTACI Infects the lungs primarily. The infection may be asymptomatic (detected only by a rising antibody titer) or may produce high fever and pneumonia. Human psittacosis is not generally communicable from human to human. Although most infections are mild, some are quite severe and involve organs other than the lung. The respiratory infection typically manifests with fever, cough, dyspnea, myalgias, and headache. The most common extrapulmonary organs involved are the liver (hepatomegaly, jaundice), heart (myocarditis, pericarditis), and nervous system (hearing loss, transverse myelitis, and encephalitis). Laboratory Diagnosis Chlamydiae form cytoplasmic inclusions, which can be seen with special stains (Giemsa stain) or by immunofluorescence In general, the Gram stain is not useful as the organisms are too small to visualize within the cytoplasm.. Nucleic acid amplification tests (NAATs) using the patient’s urine are widely used to diagnose chlamydial sexually transmitted disease. Chlamydial antigens can also be detected in exudates or urine by enzyme-linked immunosorbent assay (ELISA). Serologic tests are used to diagnose infections by C. psittaci and C. pneumoniae but are rarely helpful in diagnosing disease caused by C. trachomatis because the frequency of infection is so high that many people already have antibodies.  Treatment; all chlamydiae are susceptible to tetracyclines, such as doxycycline, and macrolides, such as erythromycin and azithromycin. Prevention; against C. trachomatis sexually transmitted diseases is to limit transmission by safe sex practices and prompt treatment of both the patient and the sexual partners, including persons who are asymptomatic. Screening of sexually active, asymptomatic young women and treatment of those who are positive is costeffective because it may prevent PID and ectopic pregnancy. Oral erythromycin given to newborn infants of infected mothers can prevent inclusion conjunctivitis and pneumonitis caused by C. trachomatis Psittacosis in humans is controlled by restricting the importation of psittacine birds, treating or destroying sick birds, and adding tetracycline to bird feed. Domestic flocks of turkeys and ducks are tested for the presence of C. psittaci.