Related Experiment Video
Updated: Jul 19, 2026
Amikacin Protection Assay for Quantification and Visualization of Escherichia coli Cell Invasion
Published on: July 3, 2026
Comparison of media for the isolation of Enterobacter sakazakii
Carol Iversen1, Stephen J Forsythe
1School of Biomedical and Natural Sciences, Nottingham Trent University, Clifton Lane, Nottingham NG11 8NS, United Kingdom.
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 alpha-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 degrees 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.
Insights
A new enrichment broth (ESE) effectively recovers all Enterobacter sakazakii strains, unlike existing methods. This is crucial for detecting the pathogen in powdered infant formula (IFM) and ensuring infant safety.
Area of Science:
- Microbiology
- Food Safety
- Clinical Diagnostics
Background:
- Enterobacter sakazakii is a pathogen linked to neonatal infections.
- It can be present in powdered infant formula (IFM) at low levels.
- Existing culture methods sometimes fail to detect all E. sakazakii strains.
Purpose of the Study:
- To develop and evaluate a novel enrichment broth for improved recovery of Enterobacter sakazakii.
- To compare the efficacy of the new broth against existing methods for E. sakazakii detection in IFM.
Main Methods:
- Comparison of four enrichment broths: Enterobacteriaceae enrichment broth (EE), E. sakazakii selective broth (ESSB), modified lauryl sulfate broth (mLST), and a novel E. sakazakii enrichment broth (ESE).
- Evaluation of selective agars (E. sakazakii isolation agar and Druggan-Forsythe-Iversen agar) for E. sakazakii isolation.
- Testing recovery of desiccated E. sakazakii from IFM with competing flora.
Main Results:
- The novel ESE broth achieved 100% recovery of 177 E. sakazakii strains, while other broths had 2-6% failure rates.
- Druggan-Forsythe-Iversen agar supported growth of more strains than E. sakazakii isolation agar, though the latter had fewer false positives.
- A small percentage (2%) of strains lacked typical yellow pigmentation on a common diagnostic agar.
Conclusions:
- Current methods for E. sakazakii isolation and identification may not detect all strains.
- The novel ESE enrichment broth offers superior recovery rates for E. sakazakii.
- Improvements in diagnostic media are needed to accommodate the full phenotypic range of E. sakazakii.
