Distribution and Evolution of the Palatinose (pal) operon in Enterobacter sakazakii

Abstract

Enterobacter sakazakii, an opportunistic enteric pathogen found in infant milk formula, is associated with outbreaks of meningitis and septicemia among immunocompromised newborns. A biochemical signature of E. sakazakii metabolism is its ability to degrade palatinose. The prevalence of the pal operon among E. sakazakii remains unknown. Studying 144 E. sakazakii strains, the prevalence of five pal genes (palZ, K, Q, E, and G) were assessed. Only 22% of strains retained all five genes in the pal operon, while another 22% of strains retained four of the five genes. Genetic instability of the pal operon was seen in phylogenetic studies which revealed evidence for horizontal gene transfer of the pal genes among strains and revealed variation in the structure and distribution of the pal operon. The genetic instability of the pal genes inferred from this study rejects using this operon as a diagnostic target for E. sakazakii detection in infant formula.