Antibacterial Mechanism of Dellaglioa algida against Pseudomonas fluorescens and Pseudomonas fragi

Pseudomonas fluorescens (P. fluorescens) and Pseudomonas fragi (P. fragi), two kinds of psychrotrophic Pseudomonas species with pathogenicity, are likely to contaminate foods and cause diseases even in fairly cold environments, an outcome which should be suppressed. This paper investigates the antibacterial mechanisms of Dellaglioa algida (D. algida), a new type of low-temperature-resistant Lactobacillus, on two such Pseudomonas. By the enzyme treatment approach, the antibacterial substance existing in the cell-free supernatant (CFS) of D. algida is preliminarily determined as organic acid or protein; then, its inhibition effects are assessed under various culture environments, including pH value, salinity, and culture time, where the best antibacterial performance is achieved at pH = 6.00, S = 0%, and culture time = 48 h. A series of experiments on biofilms indicate that D. algida is not only able to inhibit the generation or damage the integrality of the biofilm of the two mentioned Pseudomonas, but also can reduce the motility, including swarming and swimming, of P. fragi and restrain the swarming of P. fluorescens. The aformentioned developed antibacterial mechanisms show the possibility of using D. algida in applications as an inhibitor for psychrotrophic Pseudomonas in the food industry, by virtue of its strong suppression capability, especially in cold environments.