Hemolytic activity of Prevotella intermedia and Prevotella nigrescens strains: influence of abiotic factors in solid and liquid assays.

The research article investigates how various abiotic factors affect the hemolytic activity of specific strains of the bacteria Prevotella intermedia and Prevotella nigrescens. It was observed that factors like growth medium, blood source, presence of certain compounds, and incubation atmosphere influenced the hemolytic activity of these bacteria.

Identification of Influencing Factors

• The study found that the medium of growth significantly affected the hemolytic activity of these bacteria (where hemolytic activity refers to the ability of the bacteria to disrupt red blood cells). In particular, brain heart infusion agar was identified as the medium that promoted the most hemolytic activity when incubated in a Brewer-like anaerobic environment for 48 hours.
• It was also noted that the expression of hemolytic activity was less intense and delayed when certain compounds, specifically hemin and menadione, were present in solid media.

Blood Source Specificity

• Another important observation was the influence of blood source in the hemolytic activity of these bacteria. It was found that beta-hemolysis (complete lysis of red blood cells) was detected in media supplemented with horse or human blood, while alpha-hemolysis (partial lysis of red blood cells) was seen when sheep blood was used.
• Furthermore, in experiments with liquid media, sheep erythrocytes (red blood cells) were found to be resistant to hemolysis, while horse and human cells where lysed (broken down). This hints at a certain specificity in the hemolytic activity of the bacteria, dependent on the source of the blood.

Study of Hemolytic Stability

• When liquid assays were carried out, it was observed that the hemolytic activity of all strains tested remained stable over a pH range of 6.0 to 8.5. This implies the bacterial strains maintain their ability to lyse red blood cells under these pH conditions.
• Additionally, the presence of iron-scavenging compounds (compounds that can bind to and collect free iron in a system) or changes in the incubation atmosphere did not seem to alter this activity.

Exclusion of Mechanism

• Finally, the researchers ruled out the phenomenon of hot/cold hemolysis as the mechanism of action for the hemolysin produced by P. intermedia and P. nigrescens. Hot/cold hemolysis refers to a process where red blood cells bind the hemolysin at low temperature and lyse upon warming; however, this was deemed not applicable for these specific bacteria.