Distribution, prevalence and persistence of Cronobacter (Enterobacter sakazakii) in the nonprocessing and processing environments of five milk powder factories

Aims: To characterise the occurrence of Cronobacter in milk powder factories. Methods and Results: Cronobacter was isolated from 32% of 298 environmental samples from five factories. More isolations occurred in nonprocessing (49%) than processing areas (29%), although the greatest occurrence was in a single milk powder area during shutdown maintenance (81%) and the lowest after reinstatement of production hygiene practices (6%). Clonal analysis using PFGE placed 129 isolates into 49 groups. Most clones (45) were unique to each factory and seven were isolated in both milk powder and other areas of the same factory including tanker bays, evaporator rooms, an employee's shoes and external roofs. Cronobacter was not isolated from raw milk processing areas. Within powder areas, 17 clones occurred at more than one and up to eight locations and six occurred more than once at the same location. Between four and seven clones were in the powder areas at each factory. The most prevalent and persistent clones were isolated from external roofs above spray driers, in air treatment areas and where high foot traffic occurs. Conclusions: Cronobacter is dispersed widely at milk powder factories. This study suggests that distribution is assisted by movement of air, milk powder and personnel and that new hygiene strategies will be needed to reduce prevalence. Significance and Impact of the Study: Knowledge of occurrence is essential for the development of strategies to control dissemination of Cronobacter within factories and reduce risk of entry into powdered milk products.