Effect of Origanum vulgare Essential Oil on Biofilm Formation and Motility Capacity of Pseudomonas fluorescens Strains Isolated from Discoloured Mozzarella Cheese

The study was focused on P. fluorescens strains isolated from Mozzarella cheese, with the aim of evaluating the effects of Origanum vulgare L. essential oil (OEO) on the biofilm formation and eradication, as well as on the motility and blue pigment production at 10°C. METHODS AND RESULTS: Microdilution method was used to determine the minimum inhibitory and bactericidal concentration of the OEO, which ranged between 10 and 40 μl ml-1 . In vitro studies demonstrated that a sub-lethal concentration of OEO influenced not only P. fluorescens growth and motility, but also the capability to form biofilm and, in a lower degree, the biofilm eradication at 10°C. Analysis by confocal microscopy revealed a dramatic reduction of biofilm formation and thickness, with scattered damage or death of cells, stained by propidium iodide. In addition, a concentration of 5 μl ml-1 of OEO affected the motility of the cells, and in particular their ability to swim. However, the essential oil did not inhibit the blue pigment production by any of the tested strains. CONCLUSIONS: The present findings suggest that oregano essential oil inhibits the biofilm formation of P. fluorescens strains and alters their motility. Moreover, in the pre-formed biofilm, OEO contributes to the detachment of the cells, deteriorating the architecture of the biofilm and reducing its thickness. SIGNIFICANCE AND IMPACT OF STUDY: The Origanum vulgare L. essential oil was revealed as a promising agent against biofilm formation and for its detaching; these results suggest that oregano EO could be used in the dairy food industry to control biofilm formation, as an alternative, or in combination with conventional sanitizers.