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Open Access Highly Accessed Research article

Bifidobacterium pseudolongum are efficient indicators of animal fecal contamination in raw milk cheese industry

Véronique Delcenserie1, Françoise Gavini2, Bernard China1 and Georges Daube1*

Author Affiliations

1 Food Sciences Department, Faculty of Veterinary Medicine, University of Liège, Sart Tilman, B43b Liege, B-4000 Belgium

2 Technologie des Produits Animaux, Institut National de la recherche agronomique, 369 rue Jules Guesde, Villeneuve d'Ascq, F-59651 France

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BMC Microbiology 2011, 11:178  doi:10.1186/1471-2180-11-178

Published: 4 August 2011

Abstract

Background

The contamination of raw milk cheeses (St-Marcellin and Brie) from two plants in France was studied at several steps of production (raw milk, after addition of rennet - St-Marcellin - or after second maturation - Brie -, after removal from the mold and during ripening) using bifidobacteria as indicators of fecal contamination.

Results

Bifidobacterium semi-quantitative counts were compared using PCR-RFLP and real-time PCR. B. pseudolongum were detected in 77% (PCR-RFLP; 1.75 to 2.29 log cfu ml-1) and 68% (real-time PCR; 2.19 to 2.73 log cfu ml-1) of St-Marcellin samples and in 87% (PCR-RFLP; 1.17 to 2.40 log cfu ml-1) of Brie cheeses samples. Mean counts of B. pseudolongum remained stable along both processes. Two other populations of bifidobacteria were detected during the ripening stage of St-Marcellin, respectively in 61% and 18% of the samples (PCR-RFLP). The presence of these populations explains the increase in total bifidobacteria observed during ripening. Further characterization of these populations is currently under process. Forty-eight percents (St-Marcellin) and 70% (Brie) of the samples were B. pseudolongum positive/E. coli negative while only 10% (St-Marcellin) and 3% (Brie) were B. pseudolongum negative/E. coli positive.

Conclusions

The increase of total bifidobacteria during ripening in Marcellin's process does not allow their use as fecal indicator. The presence of B. pseudolongum along the processes defined a contamination from animal origin since this species is predominant in cow dung and has never been isolated in human feces. B. pseudolongum was more sensitive as an indicator than E. coli along the two different cheese processes. B. pseudolongum should be used as fecal indicator rather than E. coli to assess the quality of raw milk and raw milk cheeses.