Lethal hydroxyl radical accumulation by a lactococcal bacteriocin, lacticin Q.

Area of Science:

• Microbiology
• Biochemistry

Background:

• Lacticin Q, a lactococcal bacteriocin, exhibits selective antimicrobial activity against Gram-positive bacteria.
• Its mechanism was previously described by the toroidal pore model, but selective activity suggested other factors.
• Membrane lipid composition alone did not explain the observed selective activity.

Purpose of the Study:

• To investigate the role of hydroxyl radical accumulation in the antimicrobial mechanism of lacticin Q.
• To determine if hydroxyl radical generation contributes to the selective antimicrobial activity of lacticin Q.

Main Methods:

• Exposure of indicator bacterial strains to lacticin Q at concentrations near the MIC and MBC.
• Measurement of hydroxyl radical accumulation in treated bacterial cultures.
• Assessment of cell viability following treatment with lacticin Q and hydroxyl radical scavengers.

Main Results:

• High levels of hydroxyl radicals accumulated in indicator strains upon exposure to lacticin Q.
• Treatment with hydroxyl radical scavengers (thiourea, 2,2'-bipyridyl) reduced hydroxyl radical accumulation.
• Scavenger treatment also led to the recovery of cell viability, indicating a protective effect.

Conclusions:

• Hydroxyl radical accumulation is a key factor in the antimicrobial mechanism of lacticin Q.
• This accumulation, varying by bacterial strain, underlies lacticin Q's selective antimicrobial activity.
• The final antimicrobial effect of lacticin Q involves hydroxyl radical generation, potentially independent of pore formation.