Mycoplasma and Chlamydia

• Mycoplasma


  • Spherical to filamentous cells with no cell walls
  • Fried-egg shaped colonies on agar
  • Evolved by degenerative evolution from Gram (+) and are phylogenetically most closely related to some clostridia
  • Smallest self-replicating organisms with the smallest genomes (500 to 1000 genes)
  • Low in guanine and cytosine
  • Nutritionally very exacting
  • Many require cholesterol, a unique property among prokaryotes
  • Ureaplasmas require urea for growth, another unusual property

  
• Mycoplasma


  • Have surface antigens such as membrane proteins, lipoproteins, glycolipids, and lipoglycans
  • Some of the membrane proteins undergo spontaneous antigenic variation
  • Antibodies to surface antigens inhibit growth; various serological tests have been developed and are useful in classification
  • Surface parasites of the human respiratory and urogenital tracts

  
• Mycoplasma pneumoniae attachment

  1. Attaches to sialoglycoproteins or sialoglycolipid receptors on the tracheal epithelium via protein adhesins on the attachment organelle

  2. The major adhesin is a 170-kilodalton (kDa) protein, named P1

  
• Mycoplasma pneumoniae attachment

  Hydrogen peroxide and superoxide radicals (O2–) excreted by the attached organisms cause oxidative tissue damage
• Pneumonia induced by Mycoplasma pneumoniae

  Local immunologic and phagocytic responses to the parasites
• Sequelae of M. pneumoniae infection (mainly hematologic and neurologic) apparently have an autoimmune etiology
• Several fastidious mycoplasmas may act as cofactors in activation of the acquired immunodeficiency syndrome (AIDS)
• Mycoplasma pathogenicity factors

  • Macrophage activation, cytokine induction, and super-antigen properties of some mycoplasmal cell components

  
• M. pneumoniae infection

  Disease of the upper and lower respiratory tracts
• Cough, fever, and headache may persist for several weeks in M. pneumoniae infection
• Convalescence is slow in M. pneumoniae infection
• Ureaplasma urealyticum infection


  Causes non-gonococcal urethritis in men, resulting in dysuria, urgency, and urethral discharge
• M. pneumoniae infection occurs worldwide and is more prevalent in colder months
• M. pneumoniae infection affects mainly children ages 5 to 9 years
• M. pneumoniae infection is spread by close personal contact and has a long incubation period
• Ureaplasma urealyticum is spread primarily through sexual contact
• Women may be asymptomatic reservoirs for Ureaplasma urealyticum
• Culture of M pneumoniae from sputum or a throat swab is possible, but very slow; therefore diagnosis is usually based on serologic tests
• There is no certified vaccine for M. pneumoniae
• Treatment with erythromycin or tetracyclines is effective in reducing symptoms in both M pneumoniae and U urealyticum infections
• Chlamydia

  • Obligate intracellular bacteria
  • Lack several metabolic and biosynthetic pathways and depend on the host cell for intermediates, including ATP
• Chlamydia stages

  Infectious particles called elementary bodies<|>Intracytoplasmic, reproductive forms called reticulate bodies
• Chlamydia species

  • C. trachomatis
  • C. psittaci
  • C. pneumoniae
• C. trachomatis and C. psittaci contain many serovars based on differences in cell wall and outer membrane proteins
• C. pneumoniae contains one serovar—the TWAR organism
• Chlamydia


  • Have a hemagglutinin that may facilitate attachment to cells
  • The cell-mediated immune response is largely responsible for tissue damage during inflammation, although an endotoxin-like toxin has been described
  • Antibodies develop during infection, but they do not prevent reinfection
• Trachoma

  Characterized by the development of follicles and inflamed conjunctivae<|>Cornea may become cloudy and vascularized; repeated infections are a common cause of blindness<|>Occurs worldwide and is prevalent in Africa and Asia
• C. trachomatis usually is inoculated into the eye by contaminated fingers or fomites or, in neonates, by passage through an infected birth canal
• Inclusion conjunctivitis

  Milder inflammatory conjunctival infection with purulent discharge
• Genital infections caused by C. trachomatis

  Non-gonococcal urethritis in men and acute salpingitis and cervicitis in women<|>Lymphogranuloma venereum, a venereal disease with genital lesions and regional lymph node involvement (buboes)
• Genital infections are spread venereally, and respiratory infections usually by inhalation
• Psittacosis


  Influenza-like illness caused by C. psittaci, acquired from infected birds
• C. pneumoniae (TWAR organism)


  Causes atypical pneumonitis in humans
• Clinical presentation of psittacosis is often diagnostic
• Diagnosis may be confirmed by serology (complement fixation or microimmunofluorescence tests) on sera and/or tears
• Tetracycline and erythromycin are the drugs of choice for treating Chlamydia infections
• Penicillin is not effective for treating Chlamydia infections