Identification of Enterobacteriaceae isolates from raw ingredients, environmental samples and products of an infant formula processing plant

Over the past few years the group of Enterobacteriacece has considerably gained in importance for food industries, especially for infant formula processing plants. Up to now, only a few studies have focused on the diversity of this group in powdered infant formula and related products, Therefore, the aim of this study was to identify Enterobacteriacece isolates from a previous study from different samples of an infant formula processing plant. A total of 470 isolates from raw ingredients (n = 117), environmental samples (n = 166) and finished products (n = 187) were further identified by biochemical tests as well as by rpoB sequencing. The most common species was Enterobacter cloacae (n = 161), followed by Pantoea spp. (n = 51) and Klebsiella pneumoniae (n = 39). In total, 65 isolates could not be identified. Using the partial rpoB gene sequence data as a similarity matrix, 22 different clusters could be formed within these 65 isolates. The fact that some isolates from the same rpoB cluster originate from different sample types might indicate that they are widely common within such a production environment and hence of practical relevance. These isolates which form possibly novel genus/species will be further investigated.