The phenotypic and genotypic characterization of Enterobacter sakazakii strains from infant formula milk

Enterobacter sakazakii is an emerging foodborne pathogen associated with severe diseases in neonates. Infant formula milk (IFM) has been identified as one of the major contaminated sources and a transmission vehicle. To determine the phenotypic and genotypic characterization of this pathogen, 22 E. sakazakii strains isolated from IFM by an FDA-recommended method and PCR on the alpha-glucosidase gene were subtyped by random amplified polymorphic DNA (RAPD)-PCR, enterobacterial repetitive intergenic consensus (ERIC)-PCR, and antibiotic resistance patterns. At a similarity threshold of 80%, 16 ERIC-PCR fingerprint types were identified with a discriminatory power (D) of 0.933, and 18 RAPD-PCR types were identified with D of 0.973. Resistance to 9 antibiotics tested by disk diffusion assay revealed 6 antibiotic resistance patterns with D of 0.749. The comparison of characterization indicated that RAPD-PCR and ERIC-PCR have high discriminatory power showing genetic diversity of E. sakazakii isolates, and ERIC-PCR patterns showed a closer correlation than RAPD-PCR patterns to phenotypic characterization and the brands of IFM. Overall, the ERIC-PCR typing method could be used for tracing sources of E. sakazakii isolates in the food chain.