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11 March 2004

FASTER DETECTION OF ENTEROBACTER SAKAZAKII IN INFANT FORMULA

As many readers will know, there is an increasing concern in the food industry about the occurrence of Enterobacter sakazakii infections in neonates who have been fed milk-based powdered infant formula. To assist food laboratories in the testing of these products, Oxoid has introduced Oxoid Chromogenic Enterobacter sakazakii Agar (Druggan-Forsythe-Iversen (DFI) formulation) that allows recovery and detection of E. sakazakii in just 3 days – 2 days faster than by conventional methods.

Enterobacter sakazakii is a Gram-negative rod-shaped bacterium within the family Enterobacteriaceae. The organism was called "yellow-pigmented Enterobacter cloacae" until 1980 when it was renamed Enterobacter sakazakii ¹. Urmenyi and Franklin reported the first two known cases of meningitis caused by E. sakazakii in 1961. Subsequently, cases of meningitis, septicaemia, and necrotizing enterocolitis due to E. sakazakii have been reported worldwide.

Infants born prematurely and those with underlying medical conditions are at the highest risk of developing E. sakazakii infection. Clusters of E. sakazakii infections linked to powdered infant formula products from various manufacturers have been reported in a number of countries. Outbreaks have also occurred in neonatal intensive care units worldwide ².

In 2002 the FDA published a recommended method for isolating and identifying E. sakazakii from infant formula: pre-enrichment in sterile water and enrichment in EE Broth is followed by plating onto VRBG Agar then sub culture onto Tryptone Soya Agar. Yellow-pigmented colonies are confirmed as E. sakazakii by oxidase and other biochemical tests.

When compared to the current FDA method, all clinical and food strains of E. sakazakii (95/95) were detected on the new Oxoid chromogenic Enterobacter sakazakii Agar (DFI formulation) two days sooner than the alternative method ³.

Pre-enrichment and selective enrichment are followed by plating samples onto Oxoid Chromogenic Enterobacter sakazakii Agar ( DFI formulation ). This innovative new chromogenic medium contains the substrate 5-bromo-4-chloro-3-indolyl-α, D-glucopyranoside which is cleaved by the enzyme α-glucosidase, expressed by E. sakazakii, to form easily distinguishable blue-green colonies.

For more information please contact Val Kane, Oxoid Ltd, telephone: +44 (0) 1256 841144, fax: +44 (0) 1256 329728 or email: val.kane@oxoid.com.

References

1. Lai KK. Enterobacter sakazakii infections among neonates, infants, children, and adults. Medicine 2001;80:113-22.
2. van Acker et al. Outbreak of necrotizing enterocolitis associated with Enterobacter sakazakii in powdered milk formula. J Clin Microbiol 2001;39:293-97
3. Data on file at Oxoid Ltd.