Is Lactobacillus Gram-Positive? A Case Study of Lactobacillus iners

Area of Science:

• Microbiology
• Human Microbiome Studies
• Bacterial Pathogenesis

Background:

• Lactobacillus iners is the most common bacterium in the human vaginal microbiome.
• The genus Lactobacillus is typically Gram-positive, but L. iners sometimes appears Gram-negative.
• This discrepancy can complicate the diagnosis of bacterial vaginosis.

Purpose of the Study:

• To investigate the reason behind the Gram-negative stain appearance of Lactobacillus iners.
• To identify genetic factors potentially contributing to this unique phenotype.
• To understand how this characteristic influences L. iners's prevalence in the vaginal environment.

Main Methods:

• Transmission electron microscopy (TEM) to analyze cell wall thickness.
• Comparative genome analysis to identify gene differences.
• Microbiome analysis to assess bacterial prevalence.

Main Results:

• TEM revealed a thin cell wall in L. iners (17.39 ± 0.8 nm), explaining its Gram-negative appearance.
• Four genes were consistently absent in L. iners genomes compared to other Lactobacillus species.
• These findings suggest a potential link between cell wall structure, genetics, and L. iners's dominance.

Conclusions:

• The thin cell wall of L. iners is responsible for its Gram-negative staining, which may cause over-diagnosis of bacterial vaginosis.
• Specific gene absences in L. iners might underlie this unique cell wall phenotype.
• This characteristic, along with other adaptations, likely contributes to L. iners's success in the dynamic vaginal environment.