ABSTRACT: The main goal of this research was to characterize the bacterial diversity of wooden boards used for aging traditional Sicilian cheeses and to evaluate whether pathogenic bacteria are associated with these surfaces. Eighteen cheese dairy factories producing three traditional cheese typologies (PDO Pecorino Siciliano, PDO Piacentinu Ennese and Caciocavallo Palermitano) were selected within Sicily region. The wooden shelf surfaces were sampled by a destructive method to detach wood splinters as well as by a non-destructive brushing to collect microbial cells. Scanning electron microscopy showed the presence of almost continuous bacterial formations on the majority of the shelves analysed. Yeasts and fungal hyphae were also visualized, indicating a complexity of the plank communities. The amplicon library of the 16S rRNA gene V3-V4 region was pair-end sequenced using the Illumina MiSeq system allowing the identification of 14 phyla, 32 classes, 52 orders, 93 families and 137 genera. Staphylococcus equorum was identified from all wooden surfaces with a maximum abundance of 64.75%. Among cheese surface ripening bacteria, Brevibacterium and Corynebacterium were detected in almost all samples. Several halophilic (Halomonas, Tetragenococcus halophilus, Chromohalobacter, Salimicrobium, Marinococcus, Salegentibacter, Haererehalobacter, Marinobacter and Idiomarinaceae) and moderately halophilic (Salinicoccus, Psychrobacter and Salinisphaera) bacteria were frequently identified. Lactic acid bacteria (LAB) were present at low percentages with the genera Leuconostoc, Lactococcus, Lactobacillus, Pediococcus and Streptococcus. The levels of wooden shelf viable microorganisms ranged between 2.4 and 7.8 log CFU/cm2. In some cases, LAB were counted at very high levels (8.2 log CFU/cm2). Members of Enterobacteriaceae family were detected in a viable state only for six samples. Coagulase positive staphylococci, Salmonella spp. and Listeria monocytogenes were not detected. Seventy-five strains belonged to Leuconostoc, Lactococcus, Pediococcus, Enterococcus, Lactobacillus and Weissella genera. IMPORTANCE This study provides evidence for the lack of pathogenic bacteria on the wooden shelves used to ripen internal bacterially ripened semi-hard and hard cheeses produced in Sicily. These three cheeses are non-inoculated on their surfaces and surface ripening is not considered to occur or, at least, not at the same extent of surface inoculated smear cheeses. Several bacterial groups identified from the wooden shelves are typically associated with smear cheeses strongly suggesting that PDO Pecorino Siciliano, PDO Piacentinu Ennese and Caciocavallo Palermitano cheese rind contributes to their final organoleptic profiles.
