Transient sensitivity to nisin in cold-shocked Gram negatives

Area of Science:

• Food Microbiology
• Bacteriology
• Antimicrobial Agents

Background:

• Gram-negative bacteria pose significant food safety risks.
• Nisin is a bacteriocin with known antimicrobial properties.
• Cold shock can affect bacterial cell membrane integrity.

Purpose of the Study:

• To investigate the combined effect of rapid chilling and nisin on Gram-negative bacterial populations.
• To determine the mechanism behind nisin's efficacy during cold shock.
• To assess the effectiveness of nisin and chilling in a food matrix.

Main Methods:

• Dose-dependent application of nisin during rapid chilling of bacterial cultures.
• Microscopic examination for structural damage to bacterial outer membranes.
• Testing nisin efficacy when added post-chilling.
• Evaluation of chilling shock, nisin, and EDTA combinations on chicken skin.

Main Results:

• Nisin exhibited a dose-dependent reduction in Gram-negative bacteria populations (Pseudomonas aeruginosa, Pseudomonas fragi, Salmonella enteritidis, Escherichia coli) during rapid chilling.
• No significant structural damage to the outer membrane was observed.
• Nisin addition after chilling had no significant effect.
• Combined chilling shock, nisin, and EDTA showed reduced efficacy on chicken skin compared to broth cultures.

Conclusions:

• Rapid chilling in the presence of nisin induces a transient susceptibility in Gram-negative bacteria, likely due to lipid phase changes in the outer membrane.
• Nisin's effectiveness is dependent on its presence during the chilling process.
• Bacterial reduction is less effective in food matrices like chicken skin due to physical buffering and nisin binding.