Identification of Enterobacteriaceae and Cronobacter spp. in raw milk, milk concentrate and milk powder: prevalence and genotyping

Cronobacter spp. (former Enterobacter sakazakii) are occasional contaminants of powdered infant formula (PIF) and have been implicated in rare cases of neonatal infections. Surveys on the prevalence of these organisms and/or contamination routes during the processing of the infant formula are of importance to the manufacturers in order to reduce the level of contamination of these products. Increasing customer awareness on possible contamination of other milk powder based products intended for consumption by (older) infants posed the question about the presence of Enterobacteriaceae and especially Cronobacter spp. in products other than PIF e. g. milk concentrate (intermediate) and milk powder, both added to a variety of infant foods. It was the aim of this study to create data on the prevalence of Enterobacteriaceae and possible epidemiologic correlation of Cronobacter spp. in raw milk, milk concentrate and milk powder obtained from a Swiss milk powder production facility (2 production sites). A total of 100 raw milk samples, 91 milk concentrate samples and 172 milk powder samples were collected and tested for the presence of Enterobacteriaceae including Cronobacter spp. by cultural means. Subsets of isolates from each sample category were selected for further molecular identification and subtyping analysis. A variety of members of the Enterobacteriaceae family were observed in all types of samples, whereas Cronobacter spp. was isolated from milk powder only. Subtyping revealed a relatively high degree of heterogeneity among Cronobacter spp. isolates from both production sites suggesting continuous entry and dissemination of organisms from the production environment into the products.