Characteristics of Biofilms Formed by Co-Culture of Listeria monocytogenes with Pseudomonas aeruginosa at Low Temperatures and Their Sensitivity to Antibacterial Substances.

We assessed the properties of biofilms (BFs) formed by mono- and co-cultures of Listeria monocytogenes and Pseudomonas aeruginosa (L+P-BF) at low temperatures and examined their sensitivity to several antibacterial substances. L. monocytogenes viable counts comprised only 1-10% of total L+P-BF viable counts at 10 degrees C and 15 degrees C, indicating the significant prevalence of P aeruginosa in co-cultures. L+P-BF formed at 10 degrees C and 15 degrees C showed very high resistance to antibiotics and NaCIO. Examination of the effects of nattokinase and nisin, natural food additives with antibacterial properties, showed that their application alone failed to inhibit L+P-BF development at 10 degrees C and 15 degrees C. However, a combined treatment with nisin and ethylenediaminetetraacetic acid, a food additive that can be used as a permeabilizing agent, suppressed the formation of L+P-BF at 10 degrees C and 15 degrees C. Microscopy observations of L+P-BF did not reveal pronounced morphological changes in bacterial cell morphology. We also noted that P aeruginosa resistance to the action of nisin during BF formation was higher when it was maintained in co-culture with L. monocytogenes. The results of the present study are an important step toward developing a safe formulation of acceptable food additives that could be used for suppression of BFs formed by pathogenic bacteria during food storage.