What is Parvimonas?
Parvimonas micra is a Gram-positive anaerobic coccus that is a normal commensal organism of the human oral cavity but can cause serious invasive infections including brain abscesses, infective endocarditis, septic embolism, and intra-abdominal abscesses, particularly in patients with periodontal disease. 1, 2, 3
Microbiology and Normal Flora
- Parvimonas micra (formerly classified as Peptostreptococcus micros until its reclassification in 2006) is an anaerobic bacterium that normally resides in the oral cavity 2
- It is capable of growing and proliferating within oral biofilms and is involved in periodontal disease, leading to gingival bleeding, gingival recession, alveolar bone loss, and tooth mobility 4
- As a commensal organism, it typically exists harmlessly in the mouth but can become pathogenic under certain conditions 1
Clinical Significance and Disease Manifestations
Parvimonas micra should be considered a potential pathogen in hospitalized patients, particularly when there is evidence of periodontal disease or dental infection as a source. 5
Common Infection Sites:
- Brain abscesses of odontogenic origin, often presenting with headache and seizures 3
- Infective endocarditis with subacute presentation and high morbidity, potentially requiring valvular surgery despite appropriate antibiotics 2
- Septic embolism with multifocal infiltrates affecting lungs, liver, and spleen 1
- Intra-abdominal abscesses 4
- Periodontal and soft tissue infections 2
- Bone infections 2
Diagnostic Challenges
A critical pitfall is that Parvimonas micra is frequently not detected by standard bacterial cultures, requiring 16S ribosomal RNA gene sequencing for identification. 3
- Standard bacterial cultures of abscess fluid may be negative despite active infection 3
- Amplification of bacterial 16S rRNA with polymerase chain reaction (PCR) is strongly recommended for bacterial identification before defining infections as cryptogenic 3
- Parvimonas micra isolations are usually part of polymicrobial infections, making its pathogenic role sometimes debated 5
Source of Infection
Untreated dental infections and severe periodontitis represent the primary source of disseminated Parvimonas micra infections. 3
- Periodontal disease appears to be the main cause of disseminated infections 1
- Infected mandibular cysts and severe periodontitis can serve as the portal of entry 3
- The organism can translocate from the oral cavity to distant sites, causing serious invasive disease 1, 2
Emerging Role in Colorectal Neoplasia
- Parvimonas micra has been identified as part of microbial panels (along with Clostridium symbiosum and pks+ Escherichia coli) that may have potential to screen for and detect recurrence of colorectal neoplasia 6
- This represents an emerging area of research regarding the role of gut microbiota in cancer surveillance 6