MICROBIOLOGY
E. Sakazakii, Now Called Cronobacter Spp. and C. Sakazakii Reclassification
Mérieux NutriSciences
May 23, 2023
Why the Confusion?
Recent taxonomic changes and high-profile outbreaks have led to both misinformation and confusion about C. sakazakii. First, E. sakazakii is not the former name for C. sakazakii, it is the former name for a group of species now known as Cronobacter. Within the Cronobacter genus, there are currently seven species: C. sakazakii, C. malonaticus, C. turicensis, C. universalis, C. dublinensis, C. muytjensii, and C. condimenti. Testing for what was formerly known as E. sakazakii is now equivalent to testing for Cronobacter spp. Second, C. sakazakii is not the only species of concern to public health; all species are considered pathogenic. Cronobacter is currently not a reportable disease in the US or Europe, therefore the incidences are likely under reported.
What Should You Be Testing For?
C. sakazakii has received the most attention as it is the species most often linked to illnesses, outbreaks, and recalls associated with powdered infant formula (PIF). Given the focus on C. sakazakii, there is often a misconception that testing programs should target only this species. However, it is important to clarify that regulations in both the US (21 CFR 106.55) and Europe (Commission Regulation (EC) No 2073/2005) specify PIF must be absent of all Cronobacter species. Simply put, where it is identified as a risk, the detection method needs to include all Cronobacter spp.; species-level identification provides additional information, but it is not required.
What Method Should You Use?
Fortunately, there have been recent advancements with Cronobacter detection methods. Currently, there are several commercially available rapid methods that meet the criteria (ISO 16140-2 or AOAC OMA validation status) for an approved alternative to the conventional regulatory method (e.g., FDA BAM Chapter 29 or ISO 22964:2017). Several of the recently commercialized alternative methods have addressed the limitations of the regulatory methods, including (i) lack of validation for high analytical weights, and (ii) validation of a broader scope of matrices, including ingredients and environmental samples. Several alternative methods have also incorporated free DNA removal protocols to address potential false positives due to dead cell detection, which can be an issue with Cronobacter and dry products. Therefore, it is now possible to detect Cronobacter spp within one-two day from samples tested at 375 g using alternative rapid detection methods.
What if I Want To Know the Species?
Concerning species identification, the currently available methods can best be described as adequate. Cronobacter is still an emerging pathogen. Identification methods require large databases to differentiate species with high confidence. Presently, these databases are still being built. The Cronobacter identification methods will reliably identify an isolate as Cronobacter. However, species-level differentiation may not always be possible (or accurate). The exception to this is a whole-genome sequence (WGS)-based identification, which is often not practical for routine analysis due to the high cost and long turn-around-time. However, cheaper, non-WGS strain differentiation methods (e.g., Ribotyping) are an option for determining the relatedness (but will not provide a species identification) of two or more strains.
In summary, E. sakazakii is now Cronobacter spp. Compared to the seven other Cronobacter, C. sakazakii is likely the most prevalent; however, all species are a public health concern. The detection method a company chooses to utilize needs to detect all Cronobacter sp.
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