Effect of Lactobacillus plantarum and Pseudomonas aeruginosa culture supernatants on polymorphonuclear damage and inflammatory response

In a previous study we determined that by-products of Lactobacillus plantarum inhibited pathogenicity of Pseudomonas aeruginosa and is effective in the treatment of infected wounds. This study assesses the cytotoxic activity of acetic acid (AA), supernatants of L. plantarum and P. aeruginosa, with and without signal acyl-homoserine-lactones (AHL), and mixtures of both bacterial supernatants on human neutrophils. Cytotoxicity was determined through viability using trypan blue, apoptosis by Annexin V, necrosis by propidium iodide and intracellular pH by SNARF-1. We found that supernatants of L. plantarum caused less cytotoxicity than AA at the same extracellular pH (p < 0.05). P. aeruginosa induced a remarkable drop in intracellular pH, which was independent of extracellular pH. This intracellular acidity was correlated with a significant decrease in viability and was higher than supernatants of AHL producing P. aeruginosa (p < 0.05). When supernatants were mixed, the quantity of AHL diminished (p < 0.001) and the cytotoxic effect induced by P.aeruginosa was ameliorated by L. plantarum supernatant (p < 0.001 vs p < 0.01). These results are in agreement with the inflammatory in vivo assays determined by intradermal inoculations in Balb/c mice. Our findings will be useful for the formulation of effective and inexpensive products to resolve infected chronic wounds in our hospitals.