Identification, phylogenetic characterisation and proteolytic activity quantification of high biofilm-forming Pseudomonas fluorescens group bacterial strains isolated from cold raw milk

Abstract

Pseudomonas fluorescens group bacterial strains with high biofilm-forming ability were isolated from cold raw milk, identified based on molecular data, and their motility, biofilm-forming ability and proteolytic activity were characterised. After 48 h incubation at 7 °C, 57 out of 67 P. fluorescens group strains produced biofilms in vitro on polystyrene microplates. Six isolates with high-ability to produce biofilms were identified as Pseudomonas simiae, Pseudomonas veronii, Pseudomonas cedrina and three strains of P. fluorescens. They were able to produce high amounts of biofilm on stainless steel surface in tryptic soy broth and UHT milk. AdnA gene was detected in the six tested strains, but in two strains that did not show any modes of motility until 96 h of incubation at 7 °C, fliC gene was not detected. AprX gene and different levels of total and heat-resistant proteolytic activity were detected in the six tested strains.