Environmental surveillance of dairy processing plants for the presence of yersinia species

Abstract

Thirty dairy processing plants were surveyed to determine if the psychrotrophic nature of Yersinia influenced its environmental niche within the plants. Three hundred forty-seven samples obtained from 30 dairy processing plants were tested for the presence of Yersinia spp. Ten (33.3%) plants had one or more positive sites. A total of 20 of the 347 (5.8%) sites tested were positive for one or more species of Yersinia. Yersinia enterocolitica was present at 85% (17/20) of the positive sites. It was identified by itself on 15 occasions and twice with other species of Yersinia. Other species identified included Yersinia ruckeri in 3 of the 20 positive samples (15%); Yersinia kristensenii and Yersinia frederiksenii both in 1 of the 20 (5%) positive samples. Ten of the 20 (50%) positive samples were obtained from coolers and entrances to freezers. Yersiniapositive cooler/freezer sites were obtained from 9 of the 10 positive plants. The remaining 10 Yersinia - positive sites were from raw milk receiving areas (4/10) and drains around machinery (6/10), including an ice maker, a case washer, two holding tanks, one filler machine and a packaging area. These results reinforce both the psychrotrophic nature of Yersinia and the evidence that raw milk can be a primary source of the organism. Our findings show that sanitation schemes need to be developed for coolers and freezers to prohibit the colonization and proliferation of Yersinia within these areas. Copyright ©, International Association of Milk, Food and Environmental Sanitarians.