Partial characterization and plasmid linkage of a nonproteinaceous antimicrobial compound in a Lactobacillus casei strain of vegetable origin

Lactobacillus casei IMPC LC34 of vegetable origin produces a non-proteinace ous inhibitory compound with a broad spectrum of activity towards Gram-posi tive and Gram-negative bacteria, including pathogens. The active substance, mainly produced in the stationary phase of growth, is insensitive to prote olytic enzymes, lipase and catalase, and is stable at 121 degrees C for 30 min. The inhibitory activity was detected either at 8 degrees C or at 37 de grees C. The active compound does not contain glucidic groups, is inactivat ed by Na-metaperiodate, and its molecular mass is between 2000 and 5000 Da. Plasmid curing experiments showed that both antimicrobial compound immunit y and production determinants were encoded by an 8 8 kbp plasmid. The effec tiveness of the active agent was verified on ready-to-use vegetables, using either the Lact. casei strain or its culture supernatant fluid as inoculan t, compared with cured clone. The application potential of the Lact. casei strain or its culture supernatant fluid for assuring the microbiological sa fety of ready-to-use vegetables is discussed.