Purification and characterization of a proteinaceous compound from Pseudomonas fluorescens ATCC 948 with inhibitory activity against some gram-positive and gram-negative bacteria of dairy interest

Abstract

A proteinaceous antimicrobial compound from Pseudomonas fluorescens ATCC 948 was purified to homogeneity by chromatography steps and characterized. The compound showed a large spectrum of activity. Inhibition of thermophilic Lactobacillus, Listeria monocytogenes, Enterobacteriaceae and P fluorescens strains was mainly detected. The antimicrobial compound produced in skim milk had an apparent molecular mass of 67 kDa, was quite heat-stable (80 °C for 15 min), insensitive to lipase and α-amylase, and completely inactivated by treatment with proteolytic enzymes. A bactericidal mode of action was detected against Lactobacillus fermentum D13 chosen as indicator strain. P fluorescens ATCC 948 was not sensitive to the antimicrobial compound produced by itself. The production of the proteinaceous substance started in the early exponential phase of growth, and was highest after 72 h of incubation at 20 °C and pH 6.5. Some considerations about the nature of the antimicrobial compound are given.