Which of the following is a mechanism by which S. gordonii inhibits competitors?

• A. Quorum sensing disruption
• B. Hydrogen peroxide production
• C. Bacteriocin production
• D. Surface adhesion

Answer: (B)

Hydrogen peroxide production is a diffusible antimicrobial strategy that S. gordonii uses to curb competing microbes in the oral biofilm. It makes and releases H2O2 through the enzyme pyruvate oxidase, which converts pyruvate and oxygen into acetyl phosphate, CO2, and hydrogen peroxide. The H2O2 diffuses to nearby bacteria, causing oxidative stress and inhibiting competitors such as Streptococcus mutans and other anaerobes, helping S. gordonii to establish early in the plaque community.

This mechanism is distinct from simply sticking to surfaces or signaling-based interference. Quorum sensing disruption would mean altering communication, which isn’t the primary way S. gordonii suppresses neighbors. Surface adhesion helps with colonization but doesn’t directly kill rivals. Bacteriocin production is another antimicrobial tactic, but the well-documented, characteristic mechanism for S. gordonii’s antagonism in the oral environment is hydrogen peroxide production.