The biochemical differentiation of Enterobacter sakazakii genotypes

Background: Enterobacter sakazakii is an emergent pathogen that has been associated with neonatal infections through contaminated powdered infant milk formula. The species was defined by Farmer et al. ( 1980) who described 15 biogroups according to the biochemical characterization of 57 strains. This present study compares genotypes ( DNA cluster groups based on partial 16S rDNA sequence analysis) with the biochemical traits for 189 E. sakazakii strains. Results: Analysis of partial 16S rDNA sequences gave 4 well defined phylogenetic groups. Cluster group 1 was composed of the majority of strains (170/189) and included Biogroups 1-5, 7-9, 11, 13 and 14. Cluster 3 corresponded with Biogroup 15 and cluster 4 with Biogroups 6, 10 and 12. Cluster group 2 comprised a new Biogroup 16. For the isolates in this study, the four DNA cluster groups can be distinguished using the inositol, dulcitol and indole tests. Conclusion: This study demonstrates an agreement between genotyping ( partial 16S rDNA) and biotyping and describes a new biogroup of E. sakazakii.