Arcobacter butzleri in sheep ricotta cheese at retail and related sources of contamination at the industrial dairy plant

The study aimed to evaluate Arcobacter spp. contamination of industrial sheep ricotta cheese purchased at retail and to establish if the dairy plant environment may represent a source of contamination. A total of 32 sheep ricotta cheeses (1.5 kg/pack) packed in modified atmosphere were purchased at retail and 30 samples were collected in two sampling sessions performed in the cheese factory from surfaces in contact with food and from surfaces not in contact with food. Seven out of 32 samples (21.9%) of ricotta cheese collected at retail tested positive for A. butzleri at cultural examination; all positive samples were collected during the same sampling and belonged to the same batch. Ten surface samples (33.3%) collected in the dairy plant were positive for A. butzleri. Cluster analysis identified 32 pulsed field gel electrophoresis (PFGE) patterns. The same PFGE pattern was isolated from more than one ricotta cheese sample indicating a common source of contamination, while more PFGE patterns could be isolated in single samples indicating different sources of contamination. The results of the environmental sampling showed that A. butzleri may be commonly isolated from the dairy processing plant investigated and may survive over time as confirmed by the isolation of the same PFGE pattern in different industrial plant surface samples. Floor contamination may represent a source of A. butzleri spread to different areas of the dairy plant as demonstrated by isolation of the same PFGE pattern in different production areas. Isolation of the same PFGE pattern from surface samples in the dairy plant and from ricotta cheese purchased at retail showed that plant surfaces may represent a source of A. butzleri post-processing contamination in cheeses produced in industrial dairy plants.