Parvimonas micra is a species of bacteria characterized as a Gram-positive, anaerobic coccus, meaning it is a spherical bacterium that thrives in environments lacking oxygen. This bacterium was first identified in 1933 and has been reclassified over the years, settling on its current name in 2006. As an opportunistic pathogen, it is typically harmless but can cause infections under certain conditions.
Natural Presence in the Human Body
Parvimonas micra is a common inhabitant of the human body, existing as part of the normal collection of microorganisms, or microbiota. It is frequently found in the oral cavity, where it resides in dental plaque and the small crevices between the gums and teeth.
Beyond the mouth, its presence extends to the gastrointestinal tract, where it lives among the diverse array of bacteria in the gut. It is also considered part of the normal flora of the female genital tract. In these locations, P. micra exists as a commensal organism, meaning it coexists with the human host without causing disease.
Its presence alone is not an indication of illness. The transition from a harmless resident to a source of infection is dependent on changes in its environment or the host’s health status.
Associated Infections and Symptoms
Parvimonas micra can shift from a harmless bacterium to an opportunistic pathogen when the conditions within its environment change. This transition often occurs when there is a breakdown in the body’s natural barriers, such as tissue injury, or when the immune system is compromised. Poor dental hygiene is a significant factor, as it can lead to an overgrowth of bacteria in the mouth, creating an opportunity for infection. Dental procedures have also been identified as a potential trigger for this bacterium to enter the bloodstream and cause issues elsewhere.
The most common infections linked to P. micra are related to the oral cavity, including dental abscesses and periodontitis, which is a severe gum infection. From the mouth, the bacterium can spread to other parts of the body, leading to more serious conditions. It has been identified as a cause of bone infections (osteomyelitis) and joint infections (septic arthritis), sometimes affecting locations like the spine or hip.
Abscesses can also form in other organs, such as the brain and liver. While rare, brain abscesses caused by P. micra have been reported. General symptoms that might suggest an anaerobic infection include localized pain, swelling, and sometimes a foul-smelling discharge from the site of infection. Systemic symptoms like fever are not always present, which can make diagnosis challenging.
Diagnosis and Medical Management
Identifying a Parvimonas micra infection requires specific laboratory procedures. A definitive diagnosis is made by collecting a sample, such as pus from an abscess or fluid from an infected joint, and culturing it in a laboratory. Because the bacterium cannot grow in the presence of oxygen, it must be cultivated in a special anaerobic atmosphere using enriched culture media. Its slow growth can further delay identification. Modern techniques like MALDI-TOF mass spectrometry and 16S rRNA gene sequencing have improved the speed and accuracy of diagnosis.
Treatment for a P. micra infection involves a two-pronged approach: antibiotics and source control. The bacterium is susceptible to antibiotics used for anaerobic infections, such as metronidazole, clindamycin, and β-lactams like co-amoxicillin. However, some resistant strains have been found, making susceptibility testing necessary. A course of intravenous antibiotics is often administered, which may be continued for several weeks depending on the severity and location of the infection.
Source control is a necessary part of managing these infections and is often needed for antibiotics to be effective. This involves physically addressing the origin of the infection. Common procedures include the surgical drainage of abscesses to remove pus and infected material, or debridement, which is the removal of dead or infected tissue from a wound or bone. For dental-related infections, treating the underlying oral issue is a necessary step to prevent recurrence.