Evaluation of a New Enrichment Broth for Detection of Cronobacter spp. in Powdered Infant Formula

The aim of this study was to investigate the potential of using Al-Holy–Rasco (AR) medium, a novel broth for detection and isolation of Cronobacter spp. in infant formula milk (IFM). The new medium's composition is generic brain heart infusion broth with the addition of 1% NaCl, 15% sucrose, and 0.80 g/liter sodium deoxycholate as selective ingredients. AR broth outperformed Enterobacteriaceae enrichment broth (EE), Enterobacter sakazakii enrichment broth (ESE), modified lauryl sulfate broth, and milk as enrichment media to stimulate the growth of a cocktail of 10 strains of Cronobacter. Additionally, AR broth significantly suppressed the growth of competing non-Cronobacter Enterobacteriaceae as compared with EE, ESE, modified lauryl sulfate broth, and milk. The recovery of desiccated Cronobacter (1 to 5,000 CFU/100 g) from powdered IFM in the presence of competing non-Cronobacter Enterobacteriaceae was determined by EE, ESE, and AR broth with 10 and 15% sucrose. AR broth with 15% sucrose outperformed all other examined broths and recovered Cronobacter from all samples tested at all Cronobacter concentrations. AR broth must be validated before it can be used for rapid detection and isolation of Cronobacter from powdered IFM.

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Comparison of Media for the Isolation of Enterobacter sakazakii

Applied and Environmental Microbiology ◽

10.1128/aem.01562-06 ◽

2006 ◽

Vol 73 (1) ◽

pp. 48-52 ◽

Cited By ~ 73

Author(s):

Carol Iversen ◽

Stephen J. Forsythe

Keyword(s):

Coliform Bacteria ◽

Powdered Infant Formula ◽

Lauryl Sulfate ◽

Enterobacter Sakazakii ◽

Formula Milk ◽

Enrichment Broth ◽

Tryptone Soya Agar ◽

Infant Formula Milk ◽

Yellow Pigmentation ◽

Low Levels

ABSTRACT 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 some E. sakazakii strains do not grow in standard media for Enterobacteriaceae and coliform bacteria; therefore, a reliable method is needed for recovery of the organism. Three E. 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 of E. 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 for E. 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 more E. sakazakii strains. It was also determined that 2% of E. sakazakii strains did not produce yellow pigmentation on tryptone soya agar at 25°C, a characteristic frequently cited in the identification of E. sakazakii. The recovery of desiccated E. 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 of E. sakazakii do not support the growth of all currently known E. sakazakii phenotypes; therefore, improvements in the proposed methods are desirable.

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