Isolation and identification of Enterobacter sakazakii in infant milk formulas

Enterobacter sakazakii is a pathogen of increasing medical concern, due to it being implicated in cases of meningitis, sepis, and necrotizing enterocolitis associated with the consumption of contaminated infant milk formula. At present, the method adopted by the Mexican food industry for the isolation and identification of E. sakazakii is based on the methodology of the United States Food and Drug Administration (FDA). However, this procedure is laborious and requires 7 days to obtain a confirmative result. The objective of this study was to determine the presence of E. sakazakii in two types of powdered infant milk formula, using an alternative method that requires less time and a smaller sample size than the FDA protocol. We adapted Leuschner's procedure by eliminating violet red bile glucose agar (VRBG) plates and instead adopting white light incubation to stimulate yellow pigment development. This allowed for isolation of E. sakazakii from powdered infant milk formula using a smaller sample and requiring only 5 days for analysis. Results showed that 92% of formula 1 and 32% of formula 2 was positive for E. sakazakii. The high contamination level of E. sakazakii suggests the need for monitoring hygienic conditions in the manufacturing plant and to assess the prevalence of E. sakazakii in powdered infant milk formulas sold in México.