Exploring the mysterious world of oral bacteria and the scientific quest to isolate Veillonella
Have you ever considered that your mouth contains an entire universe of microscopic life? Among the hundreds of bacterial species calling your oral cavity home, there exists a peculiar genus called Veillonella - an anaerobic bacterium that doesn't feed on sugars like most oral microbes, but rather dines on the lactic acid produced by its neighbors.
These bacteria exhibit unique lactic acid fermentation capability, converting this acidic byproduct into weaker acids like acetate and propionate 7 .
Composition of Veillonella species in saliva correlates with oral hygiene status .
Associated with platinum resistance in ovarian cancer 2 .
May enhance performance through lactate metabolism 7 .
Research has revealed that V. parvula produces outer membrane vesicles that can increase specific neutrophil activity and neutrophil extracellular trap formation via ROS-PAD4 signaling, potentially contributing to inflammatory processes in conditions like periodontitis 1 .
Isolating a specific bacterial genus from a complex environment like the oral cavity, which contains hundreds of different microbial species, presents a significant scientific challenge. This is where selective media become essential tools.
A selective medium is a specially designed growth material that encourages the growth of target organisms while inhibiting others through specific ingredients.
The inclusion of basic fuchsin in Veillonella agar is particularly important, as this component causes decolorization when Veillonella species grow, making their colonies visually distinguishable from other bacteria 3 .
Recent research has refined the process of isolating and identifying Veillonella species from oral samples. One particularly illuminating study examined the composition of oral Veillonella species in Japanese children with different oral hygiene statuses .
Stimulated saliva samples from 15 Japanese children aged 4-14 years with varying oral hygiene status. These samples were immediately transferred to an anaerobic box containing 10% H₂, 85% N₂, and 5% CO₂ to protect the oxygen-sensitive Veillonella .
The saliva samples were thoroughly mixed and serially diluted with sterile phosphate buffer saline from 10⁻³ to 10⁻⁷. Aliquots of each diluted sample were then inoculated onto both general brain heart infusion (BHI) agar and the selective Veillonella agar .
Veillonella agar plates incubated for 5 days and BHI agar plates for 7 days under strict anaerobic conditions at 37°C. Bacterial colonies grown on BHI agar represented the total bacterial count, while those on Veillonella agar represented typical Veillonella colonies .
Potential Veillonella colonies were confirmed as gram-negative cocci using light microscopy after gram staining. Then, genomic DNA was extracted from these isolates .
A two-step PCR approach: First, genus-specific PCR primers (Veill-rpoBF and Veill-rpoBR) confirmed isolates as Veillonella. Then, a one-step PCR method with species-specific primers identified the exact Veillonella species .
The study yielded fascinating results about the relationship between Veillonella species distribution and oral hygiene:
| Oral Hygiene Group | Predominant Species | Secondary Species | Notable Patterns |
|---|---|---|---|
| Good (OHI-S: 0-1.2) | V. rogosae (predominant) | V. dispar, V. tobetsuensis | Highest V. rogosae prevalence |
| Moderate (OHI-S: 1.3-3.0) | V. rogosae | V. dispar, V. parvula | Transitional pattern |
| Poor (OHI-S: 3.1-6.0) | V. parvula (prevalent) | V. rogosae, V. dispar | Significantly lower V. rogosae |
The data revealed that while V. rogosae was the predominant species across all groups, its prevalence was significantly lower in children with poor oral hygiene. Conversely, V. parvula became the prevalent species in the poor oral hygiene group .
Interestingly, approximately 10% of the isolated Veillonella strains could not be classified into any established species through the standard PCR method. Further phylogenetic analysis showed these unknown strains were most closely related to V. infantium, suggesting the potential discovery of new Veillonella species or subspecies .
| Reagent/Equipment | Primary Function | Veillonella-Specific Application |
|---|---|---|
| Veillonella Agar | Selective growth medium | Contains basic fuchsin for visual identification; supports Veillonella while inhibiting competitors |
| Anaerobic Chamber | Creates oxygen-free environment | Essential for cultivating oxygen-sensitive Veillonella (10% H₂, 85% N₂, 5% CO₂) |
| Brain Heart Infusion (BHI) Agar | General growth medium | Grows total cultivable bacteria for comparison with selective medium |
| rpoB Gene Primers | Molecular identification | Species-specific identification of Veillonella through PCR |
| Basic Fuchsin | Diagnostic dye | Decolorization indicates potential Veillonella growth |
| Sodium Lactate | Metabolic substrate | Capitalizes on Veillonella's unique lactate metabolism in selective media |
While traditional culture methods remain important, molecular techniques like real-time quantitative PCR (qPCR) and droplet digital PCR (ddPCR) have emerged as powerful alternatives for detecting and quantifying Veillonella in clinical samples 8 .
These methods offer different advantages - while qPCR has a wider detection range (10³ to 10⁸ CFU/mL), ddPCR is more suitable for detecting low-abundance Veillonella samples (10¹ to 10⁴ CFU/mL) due to its superior sensitivity 8 .
The correlation between Veillonella species distribution and oral hygiene status suggests these bacteria could serve as valuable biomarkers for assessing oral health .
The shift from V. rogosae dominance to V. parvula prevalence in poor oral hygiene provides a measurable indicator that could potentially be developed into diagnostic tools.
The metabolic activities of Veillonella species also have significant implications for oral ecology. By consuming lactic acid - a key contributor to tooth demineralization and cavities - Veillonella may play a protective role against dental caries 6 .
This positions them as potential allies in maintaining oral health, particularly through their metabolic interactions with cariogenic bacteria like Streptococcus mutans 6 .
Developing more sensitive and specific techniques for Veillonella identification
Exploring how different Veillonella species influence oral and systemic health
Identifying potential new Veillonella species in oral cavities
As research continues, the humble selective medium for Veillonella remains a cornerstone tool - a simple yet sophisticated way to isolate and study these fascinating bacteria that play such a crucial role in our oral ecosystems and beyond. The silent hunt for Veillonella through the oral jungle continues, promising new discoveries at the intersection of microbiology, dentistry, and human health.