Microbial analysis of Malaysian tempeh, and characterization of two bacteriocins produced by isolates of Enterococcus faecium.

Abstract

Isolation of bacteriocinogenic lactic acid bacteria (LAB) from the Malaysian mould-fermented product tempeh and characterization of the produced bacteriocin(s). LAB were present in high numbers in final products as well as during processing. Isolates, Enterococcus faecium B1 and E. faecium B2 (E. faecium LMG 19827 and E. faecium LMG 19828, respectively) inhibited Gram-positive indicators, including Listeria monocytogenes. Partially purified bacteriocins showed a proteinaceous nature. Activity was stable after heat-treatment except at alkaline pH values. Both strains displayed a bacteriostatic mode of action. Bacteriocin production was associated with late exponential/early stationary growth. Molecular mass, calculated by SDS-PAGE, was 3.4 kDa for B1 bacteriocin, and 3.4 kDa and 5.8 kDa for B2 bacteriocins. PCR screening of enterocin-coding genes revealed three amplified fragments in total genomic DNA that may correspond with PCR signals for enterocin P, enterocin L50A and enterocin L50B. Both B1 and B2 contained a 42-kb plasmid. No differences in bacteriocinogenic capacity were found between wild type strains and plasmid-cured strains. It was possible to isolate bacteriocinogenic E. faecium active against various Gram-positive bacteria from final products of tempeh. A first step in applying biopreservation to fermented South-east Asian foods is to obtain bacteriocinogenic LAB from this source. Such isolates may also be used for biopreservation of mould-fermented foods in general, including various types of mould-ripened cheese.