Indigenous microorganisms from iceberg lettuce with adherence and antagonistic potential for use as protective culture.

摘要

The antagonistic effect of the indigenous microflora on pathogens was investigated by using Salmonella Typhimurium, Staphylococcus aureus and Listeria innocua as challenge microorganisms. 18 strains strongly adherent to the leaves of iceberg lettuce were selected and their taxonomic status was determined with the aid of API NE20, BBL CRYSTALTM E/NF systems and 16 S rDNA sequencing. In the majority of cases (15/19), the identification by biochemical testing did not agree with that of 16 S rDNA sequencing. Six strains exerted antagonistic effects on S. Typhimurium and L. innocua, when overnight cultures or cell free culture supernatants were investigated in the agar diffusion test. In vivo experiments showed that the inoculation of lettuce with P. putida LTH 5878 by dipping and pre-incubation decreased the numbers of S. Typhimurium, L. innocua and S. aureus below the level of detection (<100 cfu/g) after storage for 7-8 d at 4 degrees C. The dependency of the antagonistic efficacy on the numbers of P. putida LTH 5878 was determined using point inoculation. The study of the effect of the pseudomonades/pathogen ratio on the reduction of pathogens showed that the antagonistic activity of Pseudomonas is stronger against S. Typhimurium than against L. innocua. A major reduction was achieved for the counts of L. innocua at ratios of greater than 100:1 whereas for S. Typhimurium a ratio of 0.1:1 was already effective. The sensory properties of the inoculated and stored lettuce were in general better than those of the untreated control..