Occurrence and molecular characterization of Bacillus spp. strains isolated from gnocchi ingredients and ambient gnocchi stored at different temperatures

Ambient gnocchi is a potato-based product with a shelf-life of 12 months at room temperature, due to pasteurisation and incorporation of organic acids. Aim of this study was to investigate the microbiological characteristics of ambient gnocchi and their ingredients. In addition to their industrial formulation, ambient gnocchi were analysed when lactic and sorbic acids were partially or totally removed, at different storage temperatures, to identify the main microbial groups. Floury ingredients were the most contaminated, with total mesophilic count and presumptive Bacillus spp. up to 5 log CFU/g. Industrial gnocchi were stable, while gnocchi without acids showed loads up to 7 log CFU/g after 7 day at 37 °C. Bacillus spp. were isolated and characterized through rMLST, 7-loci MLST, and kSNP3 analysis. Virulence factors and antibiotic resistance determinants were detected in isolates of the Bacillus cereus group. Bacillus subtilis was the most frequently isolated species, showing spoilage potential, as observed by reddish slime on some samples during storage, but also interesting features evidenced by bacteriocin production genes. Therefore, we demonstrated that flour ingredients were the primary sources of contamination, and that Bacillus spp. was the microbial group of greatest interest for both safety and quality of this product.