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International Journal of Food Microbiology
Vol. 174, 20
14; Page: 98 - 109

Microbial biodiversity in cheese consortia and comparativeListeria growth on surfaces of uncooked pressed cheeses

Cécile Callon, Emilie Retureau, Robert Didienne, Marie-Christine Montel

INRA, URF 545 Fromagères, 20 Côte de Reyne, 15000 Aurillac, France.

Abstract

The study set out to determine how changes in the microbial diversity of a complex antilisterial consortium from the surface of St-Nectaire cheese modify its antilisterial activities. On the basis of the microbial composition of a natural complex consortium named TR15 (Truefood consortium 15), three new consortia of different species and strain compositions were defined: TR15-SC (58 isolates from TR15 collection), TR15-M (pools of isolates from selective counting media) and TR15-BHI (pools of isolates from BHI medium). Their antilisterial activities on the surfaces of uncooked pressed cheese made with pasteurised milk were compared with the activity of complex consortium TR15 and a control cheese inoculated only with starter culture (Streptococcus thermophilusLactobacillus delbrueckii). The natural consortium TR15 was the most inhibitory, followed by reconstituted consortium TR15-BHI. The dynamics of the cheese rind microbial flora were monitored by counting on media and by isolate identification using 16S rDNA sequencing and direct 16S rDNA Single Strand Conformation Polymorphism analysis. The combination of these methods showed that rind with natural consortium TR15 had greater microbial diversity and different microbial dynamics than cheese rinds with reconstituted consortia. Cheese rind with the natural consortium showed higher citrate consumption and the highest concentrations of lactic and acetic acids, connected with high levels of lactic acid bacteria such as Carnobacterium maltaromaticumVagococcus fluvialisEnterococcus gilvusLeuconostoc mesenteroidesBrochothrix thermosphacta and Lactococcus lactis, ripening bacteria such asArthrobacter nicotianae/arilaitensis, and Gram negative bacteria (Pseudomonas psychrophila andEnterobacter spp.). The highest Lmonocytogenes count was on rind with TR15-M and was positively associated with the highest pH value, high succinic and citric acid contents, and the highest levels ofMarinilactibacillus psychrotolerans and Gram positive catalase positive bacteria represented byStaphylococcus vitulinusBrevibacterium linensMicrobacterium gubbeenense and Brachybacterium tyrofermentans.
The results show that the species composition of consortium is more important than the number of species. It is likely that inhibition mechanisms differ from one consortium to another; investigating gene expression will be an effective way to elucidate microbial interactions in cheese.

Keywords: Natural antilisterial consortium; Reconstituted consortia; Biodiversity; Inhibitory activities; Uncooked pressed cheese rinds; Organic acids


 
 
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