Recombinant Cronobacter sakazakii Probable intracellular septation protein A (ESA_01553)

What is Cronobacter sakazakii and why is it significant in research?

Cronobacter sakazakii is an opportunistic pathogen associated with serious invasive infections, particularly in pre-term, low-birth weight, and/or immune-compromised neonates and infants. It has been epidemiologically linked to consumption of contaminated reconstituted powdered infant formula (PIF) and has a high mortality rate in affected populations . The bacterium is of significant research interest due to its pathogenicity and persistence in food production environments. Evidence suggests that the infectious dose is approximately 1000 colony forming units (CFU), though this is not based on assessment of highly virulent strains .

What is the probable intracellular septation protein A (ESA_01553) and what is its role in C. sakazakii?

The probable intracellular septation protein A, identified by the gene locus tag ESA_01553, is believed to play a critical role in cell division processes within C. sakazakii. As a septation protein, it likely contributes to the formation of the septum during bacterial cell division. Understanding this protein is important for researchers investigating bacterial cell division mechanisms, pathogenicity, and potential antimicrobial targets that could disrupt cell replication in this pathogen.

What growth conditions are optimal for studying C. sakazakii in laboratory settings?

Laboratory studies have demonstrated that C. sakazakii grows rapidly in reconstituted PIF, with optimal growth at 35°C. At this temperature, the growth rate is approximately 0.73 ± 0.01 log CFU/h with a lag phase of 0.45 ± 0.03 h and generation time of 0.41 h in 3000 ml volumes. At 22°C, the growth rate is slower at 0.45 ± 0.02 log CFU/h with a lag phase of 3 ± 0.05 h and generation time of 0.67 h . For researchers studying septation proteins like ESA_01553, these optimal growth conditions ensure sufficient bacterial yield and potentially more active cell division processes.

How does recombinant ESA_01553 expression vary across different C. sakazakii sequence types and what are the implications for virulence?

Expression of septation proteins, including ESA_01553, may vary across different C. sakazakii sequence types (STs). Research involving highly persistent sequence type 83 (ST83), clonal complex 65 (CC65), serotype O:7 strains has shown significant virulence potential with 90-100% mortality rates in zebrafish embryo models . When designing experiments to study ESA_01553 expression, researchers should consider using multiple clinically relevant strains, particularly those from ST83/CC65 and other sequence types associated with neonatal infections. Comparative expression analysis across strains with different virulence profiles could reveal correlations between septation protein activity and pathogenicity.

What methodological approaches are recommended for studying the localization and dynamics of ESA_01553 during C. sakazakii cellular division?

For studying the localization and dynamics of ESA_01553 during cellular division, researchers should consider a multi-faceted approach:

• Fluorescent protein tagging: Express recombinant ESA_01553 fused with fluorescent proteins (e.g., GFP) to track localization during cell division using confocal microscopy.

• Transmission electron microscopy (TEM): Similar to the methods described for visualizing C. sakazakii interactions with human brain microvascular endothelial cells (HBMEC), where samples were fixed with 2.5% glutaraldehyde for 6 hours, treated with 1% osmic acid buffer for 2 hours, dehydrated using an ethanol gradient, and embedded in resin before ultrathin sectioning (70 nm) .

• Immunofluorescence microscopy: Using antibodies specific to ESA_01553 to visualize the native protein within fixed bacterial cells at different stages of division.

• Time-lapse microscopy: To capture the dynamic changes in ESA_01553 localization throughout the cell cycle.

How does the expression and function of ESA_01553 compare between planktonic cells and biofilm-associated C. sakazakii?

This is a critical question given C. sakazakii's ability to persist in manufacturing environments for years . Researchers should design comparative experiments examining ESA_01553 expression and function in both growth states:

• RNA-seq analysis comparing transcript levels between planktonic and biofilm cells

• Protein extraction and quantification using Western blot or mass spectrometry

• Immunohistochemistry of biofilms to visualize ESA_01553 distribution

• Construction of ESA_01553 knockout mutants to assess the impact on biofilm formation

The methodology should include growing C. sakazakii biofilms on relevant surfaces (e.g., stainless steel, plastic) found in PIF manufacturing environments and comparing with matched planktonic cultures.

What are the recommended protocols for recombinant expression and purification of ESA_01553?

For effective recombinant expression and purification of ESA_01553:

• Expression system selection: E. coli BL21(DE3) is recommended for initial attempts, with alternative systems like C. sakazakii expression hosts for comparison.

• Vector design: Include a His6-tag or other affinity tag for purification, with TEV protease cleavage site for tag removal if needed for functional studies.

• Expression conditions: Optimize induction conditions (IPTG concentration, temperature, and duration) to maximize soluble protein yield. For septation proteins, lower temperatures (16-20°C) often reduce inclusion body formation.

• Purification protocol:

  • Immobilized metal affinity chromatography (IMAC)

  • Size exclusion chromatography for final polishing

  • Consider ion exchange chromatography if additional purification is needed

• Quality control: SDS-PAGE, Western blot, and mass spectrometry to confirm identity and purity.

What cell-based assays can be employed to study the role of ESA_01553 in C. sakazakii invasion and translocation across human blood-brain barrier models?

Building on established methods for studying C. sakazakii interactions with human brain microvascular endothelial cells (HBMEC) , researchers could:

• Generate ESA_01553 knockout mutants using CRISPR-Cas9 or traditional homologous recombination methods.

• Perform comparative invasion assays:

  • Culture HBMEC monolayers and infect with wild-type and ESA_01553 mutant strains

  • After 2h infection, treat with gentamicin (100 μg/mL) to kill extracellular bacteria

  • Lyse cells with 0.1% Triton X-100 and plate to count invaded bacteria

• Conduct translocation studies using transwell systems:

  • Seed HBMEC (2 × 10^4 cells/insert) onto collagen-coated transwell inserts

  • Allow tight junction formation (5 days, verified by TEER measurement)

  • Compare translocation rates between wild-type and ESA_01553 mutant strains

• Visualize invasive events using transmission electron microscopy using the protocol described in search result 2.

How should researchers interpret growth curve data when comparing wild-type and ESA_01553 mutant strains of C. sakazakii?

When comparing growth curves between wild-type and ESA_01553 mutant strains, researchers should analyze multiple parameters:

• Lag phase duration: Use DMFit Modeling (as described in the research with R^2 = 0.99) to accurately determine lag phase differences .

• Growth rate: Calculate in log CFU/h and compare using appropriate statistical methods (e.g., Tukey's test in SAS as used in previous C. sakazakii studies) .

• Generation time (GT): Calculate and compare between strains under identical conditions.

• Maximum cell density: Determine if the mutation affects the final population density.

The following table illustrates how data might be organized for comparison:

Statistical significance should be assessed with appropriate tests, and researchers should consider whether differences have biological relevance for cell division processes.

What statistical approaches are most appropriate for analyzing the impact of ESA_01553 mutations on virulence in animal models?

Based on previous C. sakazakii virulence studies using zebrafish embryo models that demonstrated 90-100% mortality rates , researchers should consider:

• Survival analysis: Kaplan-Meier survival curves with log-rank test to compare mortality rates over time between wild-type and ESA_01553 mutant strains.

• Bacterial burden quantification: Compare CFU counts in infected tissues at multiple time points, analyzing with ANOVA or non-parametric alternatives.

• Multi-factor analysis: If testing multiple strains and conditions, use factorial design analysis to assess interactions between strain type, temperature conditions, and other variables.

• Dose-response relationships: Establish LD50 values for wild-type and mutant strains by testing multiple infectious doses.

• Power analysis: Ensure sufficient sample sizes to detect biologically meaningful differences in virulence (α = 0.05, β = 0.2 recommended).

What are the common challenges in generating stable ESA_01553 knockout mutants and how can they be addressed?

Creating stable knockout mutants of septation proteins can be challenging due to their essential role in cell division. Researchers should consider:

• Conditional knockout strategies: Use inducible promoters to control expression during mutant generation.

• Partial deletions: Target non-essential domains rather than complete gene deletion.

• Complementation testing: Maintain a complementation plasmid expressing ESA_01553 during mutant generation, which can be cured after confirming viability.

• Addressing polar effects: Design knockout strategies that minimize impact on downstream genes in the same operon.

• Alternative approaches: Consider CRISPR interference (CRISPRi) for temporary knockdown rather than permanent knockout.

How can researchers address the heterogeneity in C. sakazakii populations when studying ESA_01553 function?

C. sakazakii demonstrates significant strain diversity, with heterogeneous distribution in environments like PIF . To address this when studying ESA_01553:

• Include multiple reference strains: Incorporate well-characterized strains like ATCC 29544, which has demonstrated strong invasion and translocation abilities , alongside clinical and environmental isolates.

• Sequence verification: Confirm ESA_01553 sequence across studied strains to identify natural variants.

• Single-cell techniques: Consider flow cytometry or single-cell microscopy to assess protein expression heterogeneity within populations.

• Control for growth phase: Standardize culture conditions and growth phases, as septation protein expression may vary throughout the bacterial life cycle.

• Account for plasmid presence: Determine if any plasmids (pESA3-like, pESA2-like, or pCS1-like) influence ESA_01553 expression or function, as these plasmids have been found in persistent strains .