Dialister micraerophilus

Dialister micraerophilus is a slow-growing, Gram-negative anaerobe that is part of the normal microbiota of the oral, gastrointestinal, and urogenital tracts. Although not routinely screened for, it has emerging clinical relevance as a potential opportunistic pathogen in polymicrobial and gynecologic infections.

What is Dialister micraerophilus?

Dialister micraerophilus is a Gram-negative, anaerobic, and microaerophilic coccobacillus first described in 2005. It belongs to the Dialister genus and is part of the normal microbiota of the oral cavity, gastrointestinal tract, and urogenital tract. 

Although not commonly isolated, it has been identified in clinical samples from blood, abscesses, bone, and gynecologic tissues. As an anaerobic organism, it thrives in environments with little or no oxygen.

When is Dialister micraerophilus Detection Relevant?

Detection of D. micraerophilus is not part of routine clinical screening but is relevant in two key settings:

Human Microbiome Research

It has been found in studies exploring microbial imbalance (dysbiosis), particularly in oral and urogenital environments.

Clinical Infections

Although its pathogenic role is still being defined, D. micraerophilus has been associated with various infections, including oral infections, Bartholin’s abscesses, and anaerobic bacteremia. It is especially relevant when isolated from polymicrobial samples or when anaerobic infection is suspected.

Testing and Identification of Dialister micraerophilus

Dialister micraerophilus is a fastidious, anaerobic to microaerophilic gram-negative coccobacillus that requires specific protocols for accurate recovery and identification.

Sample Types

In clinical settings, D. micraerophilus has been isolated from a variety of human specimens, including:

• Gynecologic samples (amniotic fluid, vaginal swabs, Bartholin gland)
• Bone and blood cultures
• Cutaneous and soft tissue infections (e.g., abscesses, cysts, pressure ulcers)

Recovery and Culture

D. microaerophilus grows as tiny, circular, transparent colonies on Columbia blood agar under anaerobic or microaerophilic conditions.

Its subtle morphology and slow growth make it difficult to detect in mixed cultures.

Identification

Biochemical testing is limited due to its asaccharolytic and unreactive profile in conventional assays.

Identification typically requires 16S rRNA gene sequencing. For species-level confirmation, a partial 600-bp sequence with ≥99% identity to the type strain is used.

Disk susceptibility profiles may support differentiation from Veillonella spp.:

• Susceptible to kanamycin, bile, and metronidazole
• Resistant to vancomycin and colistin

Antimicrobial Susceptibility Testing

Performed via agar dilution following CLSI M11-A6 guidelines.

Testing is recommended when D. micraerophilus is implicated in polymicrobial infections, especially if refractory to empirical treatment.

Gut Microbiome Testing for Dialister microaerophilus: Procedure and Interpretation

Microbiome testing is increasingly performed to assess microbial balance and gut health. 

Microbiome testing that includes Dialister microaerophilus is typically done through stool sample analysis. This test can be conducted using various methods, such as PCR, next-generation sequencing (NGS), or culture-based techniques. 

A stool sample is collected and analyzed to quantify the presence of Dialister microaerophilus and assess its relative abundance compared to other gut bacteria.

Always consult the ordering provider or laboratory company prior to sample collection, as special preparation, such as avoiding antibiotics or probiotics, may be necessary in the days leading up to sample collection.

Normal Reference Range

Normal reference ranges for Dialister microaerophilus can vary based on the laboratory and the microbiome composition of the healthy population. Generally, the goal is to maintain a balanced ratio of Dialister microaerophilus alongside other beneficial gut flora.

What Does the Presence or Increased Abundance of Dialister micraerophilus Mean?

Increased levels of D. micraerophilus may indicate dysbiosis or contribute to anaerobic infections. 

Its role is often context-dependent—for example, it has been detected in pure culture from a Bartholin’s abscess and in polymicrobial uterine pus in a case of bacteremia. 

Presence in sterile sites warrants clinical attention, particularly in women with pelvic or gynecologic infections. However, its detection alone doesn’t confirm pathogenicity without supporting clinical evidence.

What Does the Absence or Low Abundance of Dialister micraerophilus Mean?

The absence or reduction of D. micraerophilus generally has no diagnostic significance on its own. 

The human microbiome is complex, and changes in one species do not necessarily reflect disease. Interpretation should always consider clinical context, other microbial findings, and sample type.

Clinical and Antimicrobial Considerations

D. micraerophilus is slow-growing and may be underdiagnosed. It is best identified by 16S rRNA sequencing or MALDI-TOF mass spectrometry. 

Though susceptibility data are limited, it is often sensitive to beta-lactams (e.g., amoxicillin-clavulanate, piperacillin-tazobactam), carbapenems, and clindamycin. 

However, resistance to metronidazole has been reported, so susceptibility testing is advised when this organism is isolated from sterile or high-risk sites.

Key Takeaways for Clinicians

Dialister micraerophilus is an anaerobic, Gram-negative bacterium that may act as an opportunistic pathogen, especially in gynecologic and polymicrobial infections.

Due to slow growth and small colony size, identification often requires advanced molecular methods.

Consider this organism in persistent or recurrent anaerobic infections, especially when metronidazole treatment fails.

When isolated, antimicrobial susceptibility testing should guide therapy due to variable resistance patterns.

Order Microbiome Testing

Click here to compare testing options and order testing for microbiome balance.