Emery Haley, PhD, Scientific Writing Specialist
Mycoplasma hominis
Clinical Summary
- M. hominis is a nitrite-negative, biofilm-forming microorganism lacking a cell wall.
- M. hominis is fastidious and cannot grow in standard urine culture conditions.
- M. hominis is associated with complicated and persistent UTIs.
- In symptomatic UTI patients, M. hominis:
- Is not a contaminant (is found in catheter-collected urine specimens).
- Is pathogenic (associated with elevated urine biomarkers of infection).
Bacterial Characteristics
Gram-stain
Not Applicable (Mycoplasma species do not have a cell wall)
Morphology
Not Applicable (Mycoplasma species do not have a cell wall)
Growth Requirements
Fastidious (slow growing, prefers blood-agar)
Facultative anaerobe
Nitrate Reduction
No
Urease
Negative
Biofilm Formation
Yes
Pathogenicity
Colonizer or Pathobiont
Clinical Relevance in UTI
This fastidious organism has been considered a colonizer of the urogenital microbiome and is detected in some asymptomatic individuals.[1,2] Clinically, M. hominis is most commonly implicated in preterm labor/birth,[3] miscarriage,[4] stillbirth,[5] and intraamniotic infection,[6] as well as bacterial vaginosis (BV) [7]. M. hominis is also occasionally implicated in extra-urogenital infections in immune-compromised individuals.[8]
M. hominis UTI is an easily missed diagnosis. Firstly, M. hominis lacks nitrate reductase activity, so screening strategies involving urinalysis for nitrite positivity will be false-negative.[9,10] Secondly, M. hominis is rarely identified in clinical laboratories performing standard culture techniques for UTI diagnosis, because its lack of a cell wall structure prevents the effective use of gram-staining and morphology analyses.[11] Instead, M. hominis UTI is most often diagnosed by advanced molecular techniques, including polymerase chain reaction (PCR) and sequencing.[11]
In a study of older adult males and females with clinically suspected complicated UTI, M. hominis was detected in both midstream voided and in-and-out-catheter collected specimens indicating that it was truly present in the bladder, not simply a contaminant picked up during voiding.[12] Furthermore, elevated markers of immune system activation in the urinary tract have been measured from the same clinical urine specimens in which M. hominis was detected, indicating that the presence of M. hominis was associated with an immune response to urinary tract infection.[13–15]
M. hominis has been detected in men with culture-negative prostatitis [16] or epididymitis,[17] in women with unexplained lower urinary tract symptoms improved by azithromycin and/or doxycycline treatment,[18–21] and in women with UTI symptoms and “sterile” pyuria [22,23]. Even in young otherwise healthy women, M. hominis is frequently found in polymicrobial UTIs, where it may persist and contribute to treatment failure despite the fact that a more commonly recognized uropathogen may have been the primary source of the original UTI symptoms. [22,24]
Together, these findings indicate that M. hominis should be seriously considered as a uropathogen and demonstrate the value of detecting this organism, particularly in women with chronic or recurrent UTI symptoms and pyuria with a negative standard urine culture.
Treatment
The lack of a cell wall in M. hominis makes the organism inherently resistant to antibiotics whose mechanism of action targets cell wall components. Therefore, M. hominis is intrinsically resistant to all beta-lactam antibiotics (including penicillins, cephalosporins, monobactams, and carbapenems) and to vancomycin.
Evidence of Efficacy (Checkmarks): Doxycycline, and Levofloxacin.