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Reassessment of Cronobacter spp. originally isolated as Enterobacter sakazakii from infant food
Ömer Akineden1, Vanessa Heinrich1, Madeleine Gross2
1Chair of Dairy Science, Institute of Veterinary Food Science, Justus-Liebig University Giessen, Ludwigstrasse 21, D-35390, Giessen, Germany.
Insights
Cronobacter bacteria contaminated German infant formula, primarily two species: Cronobacter sakazakii and Cronobacter malonaticus. Genetic analysis revealed significant diversity within these species, impacting contamination control efforts.
Area of Science:
- Microbiology
- Food Safety
- Genetics
Background:
- Cronobacter species are opportunistic pathogens linked to infant illness, particularly through contaminated powdered infant formula (PIF).
- Prior to 2008, Cronobacter isolates were broadly classified as Enterobacter sakazakii, limiting understanding of species diversity.
- German PIF faced significant Cronobacter contamination issues in the early 2000s.
Purpose of the Study:
- To re-evaluate genetic, serologic, and biochemical traits of Cronobacter isolates from German PIF surveys (2003-2006).
- To determine the species diversity and genetic relatedness of Cronobacter strains implicated in PIF contamination.
- To understand the impact of species diversity on contamination source identification and elimination.
Main Methods:
- Sequencing of the fusA gene for species identification.
- Polymerase Chain Reaction (PCR) serotyping.
- Biochemical profiling.
- Pulsed-field gel electrophoresis (PFGE) analysis.
- Multilocus sequence typing (MLST) of selected isolates.
Main Results:
- All 80 isolates were identified as either Cronobacter sakazakii (73 isolates) or Cronobacter malonaticus (7 isolates).
- Five C. sakazakii serotypes and two C. malonaticus serotypes were identified.
- Biochemical profiling resulted in five distinct biogroups.
- PFGE and MLST analyses revealed high genetic heterogeneity within both species, with 16 different sequence types (STs) identified among 26 isolates.
Conclusions:
- Two Cronobacter species, C. sakazakii and C. malonaticus, were responsible for the German PIF contamination events in the early 2000s.
- Significant genetic diversity within these two species likely complicated efforts to trace and eliminate contamination sources.
- This detailed species and strain characterization provides crucial insights into historical food safety challenges.
Abstract:
Cronobacter spp. cause infant disease, several cases have been associated with powdered infant formulae (PIF). In the early 2000s, contamination of German PIF with these opportunistic pathogens was quite common. Before 2008, all isolates Cronobacter spp. had been classified as Enterobacter sakazakii, therefore little is known about species diversity within such isolates. Genetic, serologic, and biochemical traits of 80 Cronobacter isolates, originally obtained 2003-2006 within infant food surveys in Germany, were reassessed in this study. By sequencing of the fusA gene, all isolates were unambiguously assigned to two species, C. sakazakii (n = 73) and C. malonaticus (n = 7). PCR serotyping identified five C. sakazakii serotypes and two C. malonaticus serotypes, biochemical profiling yielded five biogroups. PFGE analysis also showed high heterogeneity in both species. Multilocus sequence typing of 26 selected isolates yielded 16 different sequence types (ST), including C. sakazakii ST 1 (n = 6) and the highly virulent ST 4 (n = 2). The results suggest that just two, but highly heterogeneous species were responsible for the Cronobacter contamination problem which challenged the German PIF industry in the beginning of this century. This fact may have influenced the success of efforts to identify and eliminate sources of contamination.