Spirochetes, Mycobacteria, and Other Bacteria PDF

Spirochetes, mycobacteria and other bacteria 1 Asst. Prof. Dr. Ayhan MEHMETOĞLU [email protected]  Learning objectives Characteristics of mycobacteria spp and Actinomycetes Diseases caused by mycobacteri...

Spirochetes, mycobacteria and other bacteria 1 Asst. Prof. Dr. Ayhan MEHMETOĞLU [email protected]  Learning objectives Characteristics of mycobacteria spp and Actinomycetes Diseases caused by mycobacteria and Actinomycetes Characteristics of rickettsia spp. Diseases caused by rickettsia Characteristics of spirochetes. Diseases caused by spirochetes 2 Atypical bacteria Mycobacteria and Actinomycetes 4  Mycobacteria are slender rods with lipid-rich cell walls that are resistant to penetration by chemical dyes, such as those used in the Gram stain. They stain poorly but, once stained, cannot be easily decolorized by treatment with acidified organic solvents. I. Hence, they are termed acid-fast. Overview Mycobacterial infections are intracellular, and generally result in the formation of slow- growing granulomatous lesions that are responsible for major tissue destruction. For example, Mycobacterium tuberculosis causes tuberculosis, the principal chronic bacterial disease in humans, and a leading 5 cause worldwide of death from infection. 6  Mycobacteria are long, slender rods that are nonmotile and do not form spores. Mycobacterial cell walls are unusual in that they are approximately sixty percent lipid, including a unique class of very long-chain (75 to 90 carbons), (mycolic acids). These complex with a variety of polysaccharides and peptides, creating a waxy cell surface that Mycobacteria makes mycobacteria strongly hydrophobic, and accounts for their acid-fast staining characteristic. Mycobacteria are also resistant to drying, but not to heat or ultraviolet irradiation. Mycobacteria are strictly aerobic. Most species grow slowly with generation times of 8 to 24 hours, in part because their hydrophobic surface promotes clumped growth. 7 Mycobacterium tuberculosis 8  Mycobacterium tuberculosis It is currently estimated that about one third of the world's population is infected with M. tuberculosis (tubercle bacillus), with thirty million people having active disease. In contrast to the decline of tuberculosis in the West, the incidence of the disease in some Asian and sub-Saharan African nations has dramatically increased. In some of these nations, nearly fifty percent of the HIV-infected population is co-infected with M. tuberculosis. 9  Epidemiology Patients with active pulmonary tuberculosis shed large numbers of organisms by coughing, creating aerosol droplet nuclei. The principal mode of contagion is person-to-person transmission by inhalation of the aerosol, and repeated or prolonged contact is usually required for transmission of infection. However, a single infected person can pass the organism to numerous people in an exposed group, such as a family, classroom, or hospital ward. 10 Dr. Ayham Abulaila 11  Primary disease initial phase: Primary disease initial phase: Primary tuberculosis is usually acquired via the respiratory tract; therefore, the initial lesion occurs in a small bronchiole or alveolus in the midlung periphery. The organisms are engulfed by local mononuclear phagocytes, and their presence initiates an inflammatory reaction. 12 13  Laboratory identification: Diagnosis of active pulmonary tuberculosis includes Identification of M. tuberculosis in clinical specimens. Nucleic acid amplification PCR. Culture on special agar. 14  Treatment Several chemotherapeutic agents are effective against M. tuberculosis. Because strains of the organism resistant to a particular agent emerge during treatment, multiple drug therapy is employed to delay or prevent emergence. Isoniazid, rifampin, ethambutol, streptomycin, and pyrazinamide are the principal or first-line drugs because of their efficacy and acceptable degree of toxicity 15  Prevention Latent TB chemotherapy: For individuals who are tuberculin-positive but asymptomatic. Directly observed therapy (DOT): Patient compliance is often low when multiple drug schedules last for six months or longer. Vaccines: A vaccine against tuberculosis has been available since early in the twentieth century. It is produced from Bacille Calmette-Gurin (BCG). 16 Mycobacterium leprae 17  Leprosy Worldwide an estimated ten to twelve million cases. Pathogenicity: M. leprae is transmitted from human to human through prolonged contact; for example, between exudates of a leprosy patient's skin lesions and the abraded skin of another individual. Clinical significance: Leprosy is a chronic granulomatous condition of peripheral nerves and mucocutaneous tissues, particularly the nasal mucosa. It occurs as a continuum between two clinical extremes: tuberculoid and lepromatous leprosy. 18 Actinomycetes 19  Actinomycetes Actinomycetes are a group of filamentous, branching, gram-positive organisms that easily fragment into slender rods. Although they superficially resemble fungi on morphologic grounds, they are prokaryotes of bacterial size. They are free-living, mostly soil organisms that are related to corynebacteria and mycobacteria, as well as to the streptomycetes that are sources of important antibiotics. 20 Nocardia 21  Nocardia Nocardia asteroides, Nocardia brasiliensis Nocardiae are aerobic soil organisms. Infections of humans and domestic animals are opportunistic and not transmissible from person to person. Clinical significance: The most common presentation of human nocardiosis is a pneumonia of rather chronic course with abscesses, extensive necrosis, and cavity formation. 22 Chlamydiae 23  Chlamydia is a genus of small bacteria that are obligate intracellular parasites, depending on the host cell for energy. They grow in cytoplasmic vacuoles in a limited number of host cell types. The genus is divided into three species: Chlamydia trachomatis, Chlamydia psittaci, and Chlamydia Overview pneumoniae. C. trachomatis infections cause diseases of the genitourinary tract and the eye, including many cases of nongonococcal urethritis and ocular infections such as trachoma. C. psittaci and C. pneumoniae infect various levels of the respiratory tract. For example, C. psittaci causes psittacosis, and C. pneumoniae causes 24 atypical pneumonia. 25 26  Chlamydia Trachomatis C. trachomatis is divided into a number of serotypes, which correlate with the clinical syndrome they cause. For example, C. trachomatis, the major causal agent of the syndrome, non- gonococcal urethritis (NGU), is currently the most common sexually transmitted bacterial disease in the United States. C. trachomatis can also cause eye infections, with symptoms ranging from irritation to blindness. 27 Trachoma, which is an ancient disease, was well described in Egyptian writings around 3800 B.C. It remains widely prevalent in developing areas of the world. 28  Chlamydia Psittaci Psittacosis, or more broadly, ornithosis, denotes a zoonotic disease that is transmitted to humans by inhalation of dust contaminated with respiratory secretions or feces of infected birds. The human disease usually targets the lower respiratory tract. There is an acute onset of fever, hacking dry cough, and flulike symptoms. Enlargement of liver and spleen is a frequent accompanying feature. Frank hepatitis, encephalitis, or myocarditis sometimes ensues. 29  Chlamydia Pneumoniae C. pneumoniae is a respiratory pathogen causing pharyngitis, sometimes followed by laryngitis, bronchitis, or interstitial pneumonia. It is a significant cause of community-acquired respiratory infection, occurring worldwide and without seasonal incidence. Epidemic outbreaks have been reported. 30 Dr. Ayham Abulaila 31 Rickettsia, Ehrlichia, Coxiella, and Bartonella 32  Introduction Rickettsia are Gram-negative, intracellular bacteria that have been recently classified into three phyla: Rickettsia, Ehrlichia, and Coxiella. They are the causes of spotted fevers, typhus, and similar illnesses. Ehrlichia are distinct from true rickettsiae and have four genera, of which Ehrlichia and Anaplasma are the most important in humans. Coxiella burnetii is the cause of Q fever. Bartonella are similar bacteria but are not members of the same taxonomic family. 33 Dr. Ayham Abulaila 34 Dr. Ayham Abulaila 35 Mycoplasma 36  Overview Mycoplasmas are small, prokaryotic organisms with no peptidoglycan cell walls. Extremely small in size. 37  Diseases Three Mycoplasma species are definitively associated with human disease, namely Mycoplasma pneumoniae, which is the cause of a primary atypical pneumonia, and Mycoplasma hominis and Ureaplasma urealyticum, which are associated with a variety of genitourinary diseases, such as urethritis, pelvic inflammatory disease, and intrapartum infections. 38 Spirochetes  Overview Spirochetes are long, slender, motile, flexible, undulating, gram-negative bacilli that have a characteristic corkscrew or helical shape. Depending on the species, they can be aerobic, anaerobic, or facultatively anaerobic. Some species can be grown in laboratory culture (either cell-free culture or tissue culture), whereas others cannot. Some species are free-living, and some are part of the normal flora of humans and animals. 40  Medically important Spirochetes Spirochetes that are important human pathogens are confined to three genera : Treponema (T. pallidum causes syphilis), Borrelia (B. burgdorferi causes Lyme disease, B. recurrentis causes relapsing fever), and Leptospira (L. interrogans causes leptospirosis). 41 Dr. Ayham Abulaila 42 Structural Features of Spirochetes Spirochetes have a unique structure that is responsible for motility. Periplasmic flagella that do not protrude from the cell but are oriented axially. Bundles of these endoflagella (axial filaments) propelling the cell in a corkscrew-like manner. Responsible for the ability of spirochete pathogens to penetrate and invade host tissue, just as a corkscrew penetrates cork. 43 Treponema Pallidum 44  Syphilis Syphilis is primarily a sexually transmitted disease caused by the spirochete T. pallidum. Starting with a small lesion (chancre), several progressive stages of the disease can span a period of thirty years or more, often ending in syphilitic dementia or cardiovascular damage. 45 46  Treponema pallidum The causative organism of syphilis is extremely fastidious and fragile. It cannot be cultured routinely in the laboratory, and is sensitive to disinfectants, heat, and drying. T. pallidum is so thin that it cannot be observed by conventional light microscopy, but requires immunofluorescent or dark-field techniques 47  Clinical significance Syphilis: Syphilis occurs in three stages. The first symptom of primary stage syphilis is a hard genital or oral ulcer (chancre) that develops at the site of inoculation. The average period between infection and the appearance of the chancre is about three weeks, this primary lesion heals spontaneously, but the organism continues to spread throughout the body via the lymph and blood. An asymptomatic period ensues, lasting as long as 24 weeks, followed by the secondary stage. 48  The secondary stage may be accompanied by systemic involvement, causing hepatitis, meningitis, nephritis, or chorioretinitis. Upon healing of the secondary lesions, the disease enters a latent period that can last for many years. In approximately forty percent of infected individuals, the disease progresses to a tertiary stage, characterized by degeneration of the nervous system, cardiovascular lesions such as aneurysms, and granulomatous lesions (gummas) in the liver, skin, and bones. 49 Dr. Ayham Abulaila 50  Congenital syphilis Congenital syphilis: T. pallidum can be transmitted through the placenta to a fetus after the first ten to fifteen weeks of pregnancy. Infection can cause death and spontaneous abortion of the fetus or cause it to be stillborn. Infected infants who live develop a condition similar to secondary syphilis, including a variety of central nervous system (CNS) and structural abnormalities. Treatment of the pregnant mother with appropriate antibiotics prevents congenital syphilis. 51  Laboratory identification Although treponemal spirochetes from primary and secondary lesions can be detected microscopically using immunofluorescent stain or dark-field illumination , syphilis is usually diagnosed serologically. Fluorescent treponemal antibody Absorbtion. (FTA-ABS) 52  Treatment and prevention One single treatment with penicillin is curative for primary and secondary syphilis; no antibiotic resistance has been reported. In cases of patient sensitivity to penicillin, alternate therapy with erythromycin or tetracyclines may also be effective. There is no vaccine against T. pallidum 53 Dr. Ayham Abulaila 54 Borrelia Burgdorferi 55  Borrelia Burgdorferi Members of the genus Borrelia are relatively large spirochetes that, like Treponema, have endoflagella that make them highly motile. Borrelia species are unusual among bacteria in that they have linear rather than circular plasmid and chromosomal DNA. Like T. pallidum, Borrelia do not appear to produce endotoxins or exotoxins. 56  Pathogenesis Lyme disease is caused by the spirochete B. burgdorferi, which is transmitted 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.] Mice and other small rodents serve as primary reservoirs for the spirochete, but deer and other mammals serve as hosts for the ticks. Lyme disease is currently the most common arthropod-transmitted disease in the United States, averaging at least 10,000 cases per year. 57 Dr. Ayham Abulaila 58  Clinical significance The first stage of Lyme disease begins 3 to 32 days after a tick bite, when a characteristic red, circular lesion with a clear center (erythema chronicum migrans) appears at the site of the bite. 59 Dr. Ayham Abulaila 60 Dr. Ayham Abulaila 61 Leptospira Interrogans 62  L. interrogans L. interrogans infection causes the disease leptospirosis. The organism is a slender (lepto = slender), tightly coiled, culturable spirochete with a single, thin, axial filament, and hooked ends. 63  Clinical Leptospirosis is essentially an animal disease that is coincidentally transmitted to humans primarily by water or food contaminated with animal urine. Fever occurs one to two weeks after infection, at which time spirochetes appear in the blood. Spirochetes reappear, accompanied by invasion of the liver, kidneys, and CNS. This results in jaundice, hemorrhage, tissue necrosis, and/or aseptic meningitis 64 Dr. Ayham Abulaila 65  For any question [email protected] Dr. Ayham Abulaila 66