Biofilm ecology of wooden shelves used in ripening the French raw milk smear cheese Reblochon de Savoie.

Little work has been carried out on the microbiology of wooden shelves supporting cheese during ripening, and the safety of their use during cheese ripening has frequently been asked. Microbial characterization (enumerations on specific growth media) and description of their physicochemical conditions (pH, water activity, and salt concentration) were determined on 50 wooden shelves of 3 different ages at the end of the cheese-ripening process, using cheeses from 8 farm producers. The experiments were performed during 2 different seasons (summer and autumn). Micrococci-corynebacteria and yeasts and molds were found to be the dominant microflora on the shelves. Leuconostocs, facultative heterofermentative lactobacilli, enterococci, staphylococci, and pseudomonads were also found but at lower levels. There was no statistical difference in the major microflora between shelves of different ages. Moreover, the total counts and the predominant microflora showed a surprising homogeneity between origins of cheeses. For most of the microflora enumerated, no seasonal variation was observed. Regardless of the age of the shelves, the wood had high water activity values (0.94 to 0.97), neutral pH values (7.1 to 8.3), and low salt contents (0.11 to 0.17 mg/cm2). The origins of the cheese had a statistically significant impact on water activity, pH, and salt concentration, whereas the age of the shelves did not influence these parameters. This study demonstrated the stability of the technological biofilm present on wooden shelves and will serve to enlarge the debate on the use of wood in cheese ripening.

Discrimination of Staphylococcus aureus strains from different species of Staphylococcus using Fourier transform infrared (FTIR) spectroscopy.

Staphylococcus aureus is a widespread opportunistic pathogen that can cause food-borne illness and is sometimes associated with raw milk and raw milk cheese products. The traditional taxonomic procedures for classification of staphylococcal species are time consuming and often several tests are required. FTIR spectroscopy offers a rapid method for the discrimination and identification of S. aureus strains isolated from raw milk and raw milk cheeses. FTIR spectroscopy was used to discriminate S. aureus from other species of Staphylococcus. This was achieved by using a model composed of 39 species and subspecies of Staphylococcus. The model was validated using a set of spectra of strains isolated from raw milk and different varieties of French raw milk cheese. S. aureus was successfully discriminated from the other species of Staphylococcus and all the strains of S. aureus isolated from raw milk and different varieties of French raw milk cheese were also successfully identified as such. These results demonstrated that FTIR spectroscopy is a rapid (results obtained within 24 h starting from a pure strain or a single colony) and robust method for the identification of S. aureus isolates of dairy origin and food-borne origin in general.