Electronic Thesis and Dissertation Repository

Thesis Format

Integrated Article


Master of Science


Microbiology and Immunology


Reid, Gregor


Lactobacillus crispatus is the dominant species in the vagina of many women. To add to our knowledge of its properties, the metabolic readout of twenty strains was analyzed using liquid chromatography-mass spectrometry (LC-MS). This led to a separation of the strains into two groups, Groups A and B. Notably, five Group B strains produced tyramine, known to raise vaginal pH, and make the environment more favourable to vaginal pathogens. The origin of Group B strains did not correlate with their host having bacterial vaginosis (BV), a condition associated with elevated pH. Five bacteriocins were detected in the genomes. Therefore, differences between L. crispatus vaginal strains based upon their genomes and metabolism. In absence of a correlation with the health status of the donor, it remains to be fully determined if this species is an active participant in creating a healthy state, or a bystander easily displaced by organisms causing dysbiosis.

Summary for Lay Audience

Within the vagina there is a collection of microorganisms termed the vaginal microbiome. Of these organisms the most common type in healthy women of reproductive age is Lactobacillus crispatus. To better understand this species, twenty strains were isolated from either healthy women, or women with vaginal dysbiosis, which is an imbalance of the vaginal bacteria that can have severe reproductive outcomes. The findings separated the twenty strains into two groups A and B, but this was not based on whether the women from whom they were collected were healthy or not. Rather, group B strains had characteristics that could negatively influence the vaginal environment, including the production of compounds that elevate pH to one more favourable to disease-causing bacteria. Five compounds were identified in the DNA that have the ability to inhibit or kill infection-causing bacteria. In summary, this research identified that not all L. crispatus strains are the same. Therefore, although these types of organisms have been suggested to be good probiotics, which are defined as “live microorganisms which when administered in adequate amounts confer a health benefit on the host,” care must be taken in selecting which strain has the necessary properties to improve the vaginal environment.

Included in

Bacteriology Commons