Mycoplasma hominis is Associated with BV, But Does Not Cause It; Ureaplasma Does Not Cause BV
Mycoplasma hominis and Ureaplasma species (U. urealyticum and U. parvum) do not cause bacterial vaginosis—they are part of the polymicrobial dysbiosis that characterizes BV, but are not causative agents. The distinction is critical: these organisms increase dramatically in BV but do not independently trigger the condition.
Understanding the Relationship
According to CDC guidelines, BV results from replacement of normal hydrogen peroxide-producing Lactobacillus species with high concentrations of anaerobic bacteria (Bacteroides, Mobiluncus), Gardnerella vaginalis, and Mycoplasma hominis 1. This language is important—M. hominis is listed as part of the altered flora, not as a causative organism.
Mycoplasma hominis
- M. hominis is strongly associated with BV (adjusted OR = 8.01) but only causes symptoms when BV is present 2
- In women without BV, M. hominis detection is not associated with any symptoms or clinical signs 2
- M. hominis increases "hugely in number" during BV episodes but has not been incriminated as a sole cause 3
- The organism functions as a co-factor or marker rather than a primary pathogen 4, 5
Ureaplasma Species
- Ureaplasma urealyticum and U. parvum are NOT associated with BV symptoms or signs 2
- While ureaplasmas may increase somewhat during BV (found in 40-80% of sexually mature women), they show no independent association with the condition 3
- No convincing evidence exists that antimicrobial therapy should target these organisms when treating BV 4
Clinical Implications
Do not test for or treat Mycoplasma/Ureaplasma when managing BV. The standard BV treatment regimens (metronidazole or clindamycin) target the anaerobic bacteria that drive the condition 6. While metronidazole indirectly decreases M. hominis colonization 5, this is a secondary effect, not the therapeutic goal.
Key Pitfalls to Avoid
- Multiplex PCR panels often detect and report these organisms, leading to unnecessary concern and inappropriate targeted therapy 2
- Testing for M. hominis, U. urealyticum, or U. parvum in nonpregnant women with vaginal symptoms is not recommended 2
- Culture for G. vaginalis is similarly not recommended as it lacks specificity—it can be isolated from half of normal women 1
Proper BV Diagnosis
Diagnose BV using clinical criteria (3 of 4 Amsel criteria) or Gram stain 1:
- Homogeneous white discharge adhering to vaginal walls
- Clue cells on microscopy
- Vaginal pH > 4.5
- Positive whiff test (fishy odor with KOH)
The presence of M. hominis is strongly associated with these findings (particularly clue cells, aOR = 8.08), but detecting the organism itself does not establish or refute the diagnosis 2.
Treatment Approach
Treat BV with standard regimens targeting the polymicrobial dysbiosis 6:
- Metronidazole 500 mg orally twice daily for 7 days, OR
- Metronidazole gel 0.75% intravaginally daily for 5 days, OR
- Clindamycin cream 2% intravaginally for 7 days
These regimens address the entire altered bacterial ecosystem, including incidental reduction of M. hominis, without need for specific mycoplasma-directed therapy.