17 Mycoplasma.ppt

Mycoplasma Dr. Sameer Naji, MB, BCh, MRCPath (London), PhD (UK) Basic Medical Sciences Dept. Faculty of Medicine Al-Balqa’ Applied University  Introduction  There are over 150 species in the class of cell wall-free bacteria.  In humans, four...

Mycoplasma Dr. Sameer Naji, MB, BCh, MRCPath (London), PhD (UK) Basic Medical Sciences Dept. Faculty of Medicine Al-Balqa’ Applied University  Introduction  There are over 150 species in the class of cell wall-free bacteria.  In humans, four species are of primary importance: Mycoplasma pneumoniae causes pneumonia and has been associated with joint and other infections. Mycoplasma hominis sometimes causes postpartum fever and has been found with other bacteria in uterine tube infections. Ureaplasma urealyticum is a cause of nongonococcal urethritis in men and is associated with lung disease in premature infants of low birth weight. Mycoplasma genitalium is closely related to M pneumoniae and has been associated with urethral and other infections. Growth on solid media consists principally of protoplasmic masses of indefinite shape that are easily distorted. These structures vary greatly in size, ranging from 50 to 300 nm in diameter. The morphology appears different according to the method of examination (eg, darkfield, immunofluorescence, Giemsa-stained films from solid or liquid media, and agar fixation). Culture of mycoplasmas that cause disease in humans requires media with serum or ascites fluid, growth factors such as yeast extract, and a metabolic substrate such as glucose or urea. After 2–6 days on agar medium, isolated colonies measuring 20–500 m can be detected with a hand lens. These colonies are round, with a granular surface and a dark center typically buried in the agar.  Diagnostic Laboratory Tests Specimens: Consist of throat swabs, sputum, inflammatory exudates, respiratory, urethral, or genital secretions. Microscopic Examination: Direct examination of a specimen is useless. Cultures: The material is inoculated onto special solid media and incubated for 3–10 days at 37°C with 5% CO2 (under microaerophilic conditions), or into special broth and incubated aerobically. Colonies may have a "fried egg" appearance on agar.  Serology Antibodies develop in humans infected with mycoplasmas and can be demonstrated by several methods. CF tests can be performed with glycolipid antigens extracted with chloroform–methanol from cultured mycoplasmas. HI tests can be applied to tanned red cells with adsorbed Mycoplasma antigens. Indirect immunofluorescence may be used. The test that measures growth inhibition by antibody is quite specific. M pneumoniae and M genitalium are serologically cross-reactive. Treatment Many strains of mycoplasmas are inhibited by a variety of antimicrobial drugs, but most strains are resistant to penicillins, cephalosporins, and vancomycin. Tetracyclines and erythromycins are effective both in vitro and in vivo and are, at present, the drugs of choice in mycoplasmal pneumonia. Some ureaplasmas are resistant to tetracycline.  Mycoplasma pneumoniae & Atypical Pneumonias  M pneumoniae is a prominent cause of pneumonia, especially in persons 5–20 years of age.  Mycoplasmal pneumonia is generally a mild disease. The clinical spectrum of M pneumoniae infection ranges from asymptomatic infection to serious pneumonitis, with occasional neurologic and hematologic (ie, hemolytic anemia) involvement and a variety of possible skin lesions.  The incubation period varies from 1 to 3 weeks. The onset is usually insidious, with lassitude, fever, headache, sore throat, and cough. Initially, the cough is nonproductive, but it is occasionally paroxysmal. Later there may be blood-streaked sputum and chest pain. Laboratory Tests The diagnosis of M pneumoniae pneumonia is largely made by the clinical recognition of the syndrome. Laboratory tests are of secondary value. The white cell count may be slightly elevated. A sputum Gram stain is of value in not suggesting some other bacterial pathogen (eg, S pneumoniae). Mycoplasmas can be recovered by culture from the pharynx and from sputum, but culture is a highly specialized test and is almost never done. Cold hemagglutinins for group O human erythrocytes appear in about 50% of untreated patients, in rising titer, with the maximum reached in the third or fourth week after onset. A titer of 1:64 or more supports the diagnosis. There is a rise in specific antibodies to M pneumoniae that is demonstrable by CF tests; acute and convalescent phase sera are necessary to demonstrate a fourfold rise in the CF antibodies. EIA to detect IgM and IgG antibodies can be highly sensitive and specific, but may not be readily available. Polymerase chain reaction (PCR) assay of specimens from throat swabs or other clinical material can be diagnostic, but is generally performed only in reference laboratories. Treatment Tetracyclines or erythromycins can produce clinical improvement but do not eradicate the mycoplasmas.  Mycoplasma hominis  M. hominis has been associated with a variety of diseases.  M. hominis can be cultured from the upper urinary tract in about 10% of patients with pyelonephritis.  M. hominis is strongly associated with infection of the uterine tubes (salpingitis) and tubo-ovarian abscesses; the organism can be isolated from the uterine tubes of about 10% of patients with salpingitis but not from women with no signs of disease.  M. hominis has been isolated from the blood of about 10% of women who have postabortal or postpartum fever and occasionally from joint fluid cultures of patients with arthritis. Ureaplasma urealyticum U. urealyticum has been associated with many diseases. U. urealyticum, which requires 10% urea for growth, probably causes nongonococcal urethritis in some men, but a majority of cases of nongonococcal urethritis are caused by Chlamydia trachomatis. U. urealyticum is common in the female genital tract, where the association with disease is weak. U. urealyticum has been associated with lung disease in premature low-birth-weight infants who acquired the organism during birth, but a causal effect has not been clearly demonstrated. The evidence that U. urealyticum is associated with involuntary infertility is at best marginal. Mycoplasma genitalium M. genitalium was originally isolated from urethral cultures of two men with nongonococcal urethritis, but culture of M. genitalium is difficult, and subsequent observations have been based on data obtained by using the PCR, molecular probes, and serologic tests. The data suggest that M. genitalium in men is associated with some cases of acute as well as chronic non-gonococcal urethritis. In women, M. genitalium has been associated with a variety of infections such as cervicitis, endometritis, salpingitis, and infertility.