Urogenital mycoplasmas: An overview
Classification of Uropathogenic Mycoplasmas
- Mycoplasmas pertain to the separate class Mollicutes, order Mycoplasmatales, and family Mycoplasmataceae, which includes two genera with pathogenic representatives: Mycoplasma and Ureaplasma.
- In certain clinical conditions Ureaplasma urealyticum, Ureaplasma parvum, Mycoplasma hominis, and Mycoplasma genitalium can cause human nongonococcal urethritis and some other urogenital disorders.
- These ailments are usually not found as monoinfection but predominantly as the tight association of various urogenital pathogens.
- The role of other mycoplasmal species in pathology of urogenital tract remains elusive.
Pathogenic Mycoplasmas – Basic Characteristics
- Mycoplasmas are the smallest pleomorphic bacteria, which don’t have the cell wall. Their cells are covered with thick lipid-containing membrane. They are facultative anaerobes or microaerophils with reduced metabolism.
- Mycoplasmas are membrane parasites, but they can grow on special nutrient media supplemented with serum, ascitic fluid, lipoproteins and sterols. After growth the bacteria yield round colonies of minimal sizes looking like “fried eggs”.
- When cultured within the cell lines and chicken embryos, mycoplasmas become closely attached to the membranes of affected cells.
- Basic antigens of mycoplasmas are glycolipids and proteins of variable structure.
- The virulence factors of mycoplasmas are not well-defined.
- The bacteria can generate cytotoxic hydrogen peroxide and superoxide radicals. Some strains may express hemolysins.
- Membrane fractions of mycoplasma play the role of superantigens. All mycoplasmas possess multiple adhesins.
- The bacteria are very sensitive to external influences. They are easily inactivated under the action of conventional antiseptics and disinfectants.
Pathogenesis and Clinical Findings in Mycoplasmal Urogenital Infections
- Various mycoplasmas have non-equal association with urogenital disorders. Moreover, such a relationship is hard to establish due to relatively low virulence of these bacteria.
- Isolated mycoplasmal culture may occur as nonpathogenic concomitant bacteria, which only follow infection process.
- In addition, these microbials frequently play a role in urogenital disorders only in closest associations with other urogenital pathogens (trichomonads, gardnerellas, chlamydiae and many others). Thus it remains difficult to evaluate the real contribution of mycoplasmal infection into urogenital pathology.
- Mycoplasma hominis was demonstrated in some patients with pyelonephritis, urethritis, prostatitis, salpingitis and tubo-ovarian abscesses.
- Systemic mycoplasmal infection may provoke postabortal or postpartum fever in females. Mycoplasma genitalium can be revealed in patients with nongonococcal urethritis.
- Ureaplasma urealyticum can be often found in female urogenital tract, but its role in women genital disorders remains unclear. Ureaplasmas may be isolated also in some cases of nongonococcal urethritis in men.
Laboratory Diagnosis of Mycoplasmal Urogenital Infections
- Urethral and vaginal scrapes or swabs, genital secretions are largely used for specimen collection.
- PCR has become the most valuable, rapid and sensitive test for mycoplasma detection.
- The only drawback of the method depends on reaction inability to discriminate viable and degraded microbial cells by their nucleic acids.
- The latter condition may occasionally cause false-positive test results.
- Routine culture tests for urogenital mycoplasmal infection are rarely used now. After incubation for about 1 week in special media the growth of minute “fried egg”-like colonies is observed. Further subculture is elaborated to identify bacteria by immunofluorescence.
- Plate microculture methods followed by determination of antimicrobial resistance of isolated species are more common.
- Microbial growth is detected by characteristic biochemical tests (hydrolysis of arginin for M. hominis and urea for ureaplasmas). The results can be registered in 1-2 days of incubation.
- Serological tests are of limited significance in local mycoplasmal infections.
Prophylaxis and Treatment
- The bacteria are resistant to antibiotics that inhibit cell wall synthesis (e.g., beta-lactams and vancomycin). Macrolides, azalides and tetracyclines (doxycycline) are preferable in treatment of urogenital mycoplasmal infections. Some strains develop increased resistance to tetracyclines and macrolides.
- Specific prophylaxis of infection is not available. Non-specific measures are used to prevent disease transmission.