Identification and Pathogenic Potential of <i>Bacillus cereus</i> Strains Isolated from a Dairy Processing Plant Producing PDO Taleggio Cheese

• Main Authors: Erica Tirloni, Simone Stella, Cristian Bernardi, Diletta Mazzantini, Francesco Celandroni, Emilia Ghelardi
• Format: Article
• Language: English
• Published: MDPI AG 2020-06-01
• Series: Microorganisms
• Subjects: <i>Bacillus cereus</i>; dairy plant; taleggio cheese; virulence; biofilm
• Online Access: https://www.mdpi.com/2076-2607/8/6/949

Low levels of contamination by <i>Bacillus cereus</i> at the cheese farm is essential for reducing any opportunity for growth prior consumption. In this study, <i>B. cereus</i> distribution in a plant producing Protected Designation of Origin Taleggio cheese was investigated and the virulence potential of the isolates was evaluated. Seventy-four samples were collected from Food and Non Food Contact Surfaces (FCS, NFCS), saline curd, and Taleggio. The eleven isolates were identified, typified, and clustered. Strains were tested for the production of hemolysins, hemolysin BL (HBL), phosphatidylcholine-specific phospholipase C (PC-PLC), proteases, and biofilm, and for the presence of chromosomal toxin-encoding genes (<i>sph</i>, <i>plcA</i>, <i>cytK</i>, <i>entFM</i>, <i>bcet</i>, <i>entS</i>, <i>nheA</i>, <i>nheB,</i> <i>nheC</i>). <i>B. cereus</i> was detected on NFCS, FCS, and curd, but not in Taleggio. The isolates were grouped into six clusters, and all produced PC-PLC, hemolysins, and proteases, and most of them HBL (66.7%). All the clusters harbored the <i>nheA, sph, plcA</i>, <i>entFM</i>, and <i>cytK</i> genes, and some also <i>nheB</i> (83.3%)<i>,</i> <i>nheC</i> (66.7%), <i>bcet</i> (50.0%), and <i>entS</i> (66.7%). All strains showed biofilm-forming ability. Our data reveal possible contamination of production plants and cheese curd by potentially virulent <i>B. cereus</i>, but bacterial absence in Taleggio highlights the efficacy of a proper management of the production phases in assuring consumer’s protection.