BACTE: MYCOPLASMA

• Mycoplasmataceae (class Mollicutes)
• Most clinically significant genera - mycoplasma (125 species) and ureaplasma (7 species)
• Most important species - mycoplasma pneumoniae (also called eaton agent after the investigator who originally isolated it)

  Causes respiratory tract diseases, such as tracheobronchitis and pneumonia
• Other commonly isolated pathogens include Mycoplasma genitalium, Mycoplasma hominis (urogenital tract disease), and Ureaplasma urealyticum (urogenital tract disease)
• Mycoplasma and ureaplasma organisms are the smallest free-living bacteria
• Do not have a cell wall and their cell membrane contains sterols.
• Absence of the cell wall renders the mycoplasmas resistant to penicillins, cephalosporins, vancomycin, and other antibiotics that interfere with synthesis of the cell wall
• Mycoplasma -Divide by binary fission (typical of all bacteria), grow on artificial cell-free media
• Mycoplasma - Facultatively anaerobic (except M. pneumoniae and rapidly growing M. hominis - strict  aerobe)
• Mycoplasma - Require exogenous sterols supplied by animal serum added to the growth medium
• Mycoplasma - Grow slowly, with a generation time of 1 to 16 hours, and most form small colonies that are difficult to detect without extended incubation
• Mycoplasma - Major antigenic determinants are membrane glycolipids and proteins
• Some species (e.g., M. hominis) form colonies with slightly raised centers, giving the classic “fried egg” appearance
• Mycoplasma - Often grow embedded beneath the surface of solid media
• Mycoplasma was isolated from humans and was referred to as pleuropneumonia-like organism (PPLO) à mycoplasma pneumoniae
• Mycoplasma - Susceptible to adverse environmental conditions, such as heat and drying.
• Transmission in humans can occur via direct sexual contact, from mother to child during delivery or in utero, and by respiratory secretions or fomites in cases of M. pneumoniae infections.
• Mycoplasma pneumoniae - May cause bronchitis, pharyngitis, or a relatively common respiratory infection à primary atypical pneumonia, or walking pneumonia
• Mycoplasma pneumoniae - Is milder and has a higher incidence in young adults
• Mycoplasma pneumoniae - Transmission is probably through aerosol droplet spray produced while coughing.
• Mycoplasma pneumoniae - Causes approximately 20% of reported pneumonias in the general population and up to 50% in confined populations, such as those in military settings.
• Mycoplasma pneumoniae - Drug of choice is erythromycin, doxycycline, or newer fluoroquinolones
• Mycoplasma pneumoniae - Organism is not normal flora, and isolation is always significant.
• Mycoplasma pneumoniae - Dienes or methylene blue stains can be used to visualize the colonies on agar media.
• Mycoplasma pneumoniae - Immunofluorescent stains and serology testing are used for laboratory diagnosis.
• Mycoplasma pneumoniae - Colonies are small and have a homogeneous granular appearance (“mulberry shaped”) unlike the fried-egg morphology of other mycoplasmas.
• Mycoplasma pneumoniae - Identification of isolates can be confirmed by inhibition of their growth with specific antisera.
• Mycoplasma pneumoniae - Because this organism is difficult to grow and results are typically not available for many weeks, however, most laboratories do not perform cultures.
• Mycoplasma hominis and Ureaplasma Species - Associated with infections of the urogenital tract and might play a role in bacterial vaginosis
• Mycoplasma hominis and Ureaplasma Species - Frequently isolated from asymptomatic sexually active individuals à  rate of colonization is directly related to the number of sexual partners
• Mycoplasma hominis and Ureaplasma Species - Are opportunistic pathogens
• Mycoplasma hominis - Found in the lower genitourinary tracts of approximately 50% of healthy adults but has not been reported as a cause of nongonococcal urethritis (NGU)
• Mycoplasma hominis - Invade the upper genitourinary tract and cause salpingitis, pyelonephritis, pelvic inflammatory disease (PID), or postpartum fevers.
• Mycoplasma hominis - Been reported to cause chronic inflammatory diseases, such as arthritis and cystitis, in patients with hypogammaglobulinemia
• Mycoplasma hominis - Has been reported more frequently in the urethra and rectum of homosexual men with HIV infection
• Cervicitis caused by M. hominis occurs more frequently in HIV-positive women compared with women without HIV infection
• Mycoplasma hominis - Facultative anaerobe that grows within 1 to 4 days and metabolizes arginine but not glucose
• Mycoplasma hominis - Colonies have a typical, large fried-egg appearance.
• Mycoplasma hominis - Resistant to erythromycin and occasionally to the tetracyclines.
• Mycoplasma hominis - Clindamycin has been used to treat infections caused by these resistant strains.