Comparison of Media for the Isolation of Enterobacter sakazakii

Enterobacter sakazakii is associated with neonatal infections and is occasionally present at low levels (<1 CFU/g) in powdered infant formula milk (IFM). It has been previously reported that someE. sakazakii strains do not grow in standard media forEnterobacteriaceae and coliform bacteria; therefore, a reliable method is needed for recovery of the organism. ThreeE. sakazakii enrichment broths—Enterobacteriaceae enrichment broth (EE),E. sakazakii selective broth (ESSB), and modified lauryl sulfate broth (mLST)—were compared with a novel broth designed for maximum recovery ofE. sakazakii ,E. sakazakii enrichment broth (ESE). One hundred seventy-seven strains (100%) grew in ESE, whereas between 2 and 6% of strains did not grow in EE, mLST, or ESSB.E. sakazakii possesses α-glucosidase activity, and a number of selective, chromogenic agars forE. sakazakii isolation based on this enzyme have been developed.E. sakazakii isolation agar produced fewer false-positive colonies than did Druggan-Forsythe-Iversen agar. However, the latter supported the growth of moreE. sakazakii strains. It was also determined that 2% ofE. sakazakii strains did not produce yellow pigmentation on tryptone soya agar at 25°C, a characteristic frequently cited in the identification ofE. sakazakii . The recovery of desiccatedE. sakazakii (0.2 to 2000 CFU/25 g) from powdered IFM in the presence of a competing flora was determined with various enrichment broths and differential selective media. Current media designed for the isolation and presumptive identification ofE. sakazakii do not support the growth of all currently knownE. sakazakii phenotypes; therefore, improvements in the proposed methods are desirable.