Use of surface-smear bacteria for inhibition of Listeria monocytogenes on the rind of smear cheese

Surface-smear micro-organisms isolated from Taleggio cheese were screened f or their ability to inhibit Listeria monocytogenes. Most of the isolates sh owing antilisterial activity (19% of the total) consisted of coryneform bac teria, mainly belonging to the Microbacterium lacticum species. The inhibit ory activity was observed also after growth as 5 degrees C and pH 6.0. Afte r cross-inhibition tests among inhibitory strains and between these and oth er pigmented, non-inhibitory strains, two bacterial mixtures were assayed a s surface-smear starter of Taleggio cheese. At different ripening stages (1 , 20 and 40 days), the cheese surface was contaminated with 2.5 x 10(2) cfu cm(-2) L. monocytogenes (Ohio strain) and the growth evaluated over 15 day s of incubation at 5 degrees C. Contrary to the laboratory experiments, Lis teria could not be completely inhibited on the cheese surface. With 5.5-6.0 pH range of the cheese rind, (lower than usual values), the growth of surf ace-smear bacteria was delayed, or even stopped. Nevertheless, a listeriost atic effect was achieved on the surface of cheese samples contaminated at t he end of ripening. This seemed so confirm the essential role played by sur face-smear bacteria, within the rind microflora, in controling the developm ent of contaminant micro-organisms, and by competitive bacteria in reducing the overall risks associated with soft cheese. The mechanisms involved in the selection and the growth of competing bacteria on the cheese surface ar e also discussed. (C) 1999 Academic Press.