pith. sign in

arxiv: 1906.11045 · v1 · pith:76SFA25Ynew · submitted 2019-06-21 · 🧬 q-bio.QM

Flow cytometry to assess the counts and physiological state of Cronobacter sakazakii cells after heat exposure

Paloma De-La-Cal-Sabater , Irma Caro , Javier Mateo , Maria J. Castro , Maria J. Cao , Emiliano J. Quinto This is my paper

Pith reviewed 2026-05-25 18:02 UTC · model grok-4.3

classification 🧬 q-bio.QM
keywords flow cytometryCronobacter sakazakiiheat treatmentviable but non-culturablepowdered infant formulamembrane integrityplate count methods
0
0 comments X

The pith

Flow cytometry detects Cronobacter sakazakii cells compromised by heat that plate counts miss.

A machine-rendered reading of the paper's core claim, the machinery that carries it, and where it could break.

The paper establishes that flow cytometry provides direct information on the physiological state of Cronobacter sakazakii cells after heat exposure in ways plate count methods cannot. It demonstrates that treatments at 60 or 65 C leave many cells with compromised membranes that may remain viable but non-culturable, while 100 C treatment behaves differently. This matters for assessing safety of reconstituted powdered infant formula, where such cells could pose undetected risks. The study reports good linear correlations between the two methods and concludes that flow cytometry could help lower the chance of pathogenic viable but non-culturable cells reaching consumers.

Core claim

Flow cytometry analysis showed that the percentage of compromised cells increased as the percentage of live cells increased after 100 C treatment, but after 60 or 65 C treatments the number of compromised cells decreased as live cells increased. This indicates mild temperatures do not fully eliminate the bacteria while still damaging membranes. Flow cytometry detected compromised cells not visible with classical plate counts, and linear regression analysis found good correlations between plate count results and flow cytometry results.

What carries the argument

Flow cytometry with fluorescent dyes to classify cells as live, dead, or membrane-compromised based on membrane integrity.

If this is right

  • Mild heat treatments at 60 or 65 C are not enough to guarantee safety of powdered infant formula against C. sakazakii.
  • Flow cytometry can detect compromised cells missed by plate counts, lowering the risk of viable but non-culturable pathogens in food.
  • Good linear correlations exist between plate count and flow cytometry results across the tested conditions.

Where Pith is reading between the lines

These are editorial extensions of the paper, not claims the author makes directly.

  • Routine food safety testing could add flow cytometry to catch processing failures that allow membrane-damaged cells to persist.
  • Recovery experiments on the compromised population after mild heat could test whether these cells regain culturability in formula.

Load-bearing premise

The fluorescent dyes and gating strategy correctly identify membrane-compromised but still viable cells without false classification from the heat treatment or food matrix.

What would settle it

A direct comparison of flow cytometry counts against a culture-independent viability method such as PMA-qPCR on the same heat-treated samples to check whether the compromised population matches the viable but non-culturable fraction.

Figures

Figures reproduced from arXiv: 1906.11045 by Emiliano J. Quinto, Irma Caro, Javier Mateo, Maria J. Cao, Maria J. Castro, Paloma De-La-Cal-Sabater.

Figure 1
Figure 1. Figure 1: The events are distributed according to fluorescence intensity at the two wavelengths studied. A gate was positively identified for dead cells since all of them were restricted to a very well-defined area, allowing its use as a control for future [PITH_FULL_IMAGE:figures/full_fig_p007_1.png] view at source ↗
read the original abstract

Cronobacter sakazakii is an opportunistic pathogen associated with outbreaks of neonatal necrotizing enterocolitis, septicemia, and meningitis. Reconstituted powdered infant formulae (PIF) is the most common vehicle of infection. Plate count methods do not provide direct information on the physiological status of cells. Flow cytometry (FC) has been used to gain insights into the physiological states of C. sakazakii after heat treatments, and to compare FC results with plate counts. The percentage of compromised cells increased as the percentage of live cells increased after the 100 C treatment. However, the number of compromised cells after 60 or 65 C treatments decreased as the percentage of live cells increased, showing that both mild temperatures would not be completely effective eliminating all bacteria but compromising their membranes, and showing that mild heat treatments are not enough to guarantee the safety of PIF. FC was capable to detect C. sakazakii compromised cells that cannot be detected with classical plate count methods, thus it could be used to decreasing the risk of pathogenic viable but non-culturable cells to be in the ingested food. Linear regression analysis showed good correlations between plate count results vs FC results.

Editorial analysis

A structured set of objections, weighed in public.

Desk editor's note, referee report, simulated authors' rebuttal, and a circularity audit. Tearing a paper down is the easy half of reading it; the pith above is the substance, this is the friction.

Referee Report

2 major / 2 minor

Summary. The manuscript reports an empirical comparison of flow cytometry (FC) and traditional plate counts for assessing Cronobacter sakazakii cell counts and physiological states (live vs. membrane-compromised) after heat treatments at 60°C, 65°C, and 100°C in the context of powdered infant formula safety. It claims that FC detects compromised cells missed by plate counts (potentially including VBNC cells), reports temperature-dependent trends in percentages and absolute numbers of compromised cells, and states that linear regression shows good correlations between the two methods.

Significance. If the FC method is validated with appropriate controls and quantitative data, the work could strengthen food safety assessments by highlighting limitations of culture-based methods for detecting stressed pathogens. The temperature-specific trends and correlation claims are internally consistent once absolute counts vs. percentages are distinguished, but the absence of raw data, replicates, or statistical details in the provided text limits assessment of robustness.

major comments (2)
  1. [Abstract] Abstract: The central claim that 'linear regression analysis showed good correlations between plate count results vs FC results' and that FC detects cells 'that cannot be detected with classical plate count methods' lacks any reported R² values, p-values, sample sizes, error bars, or data tables/figures. This information is load-bearing for evaluating whether the correlations support the superiority of FC over plate counts.
  2. [Abstract] Abstract/Methods (implied): No description is given of controls for food matrix effects, validation of the specific fluorescent dyes and gating strategy against heat-induced artifacts, or confirmation that membrane compromise detected by FC corresponds to viable but non-culturable states (e.g., via recovery experiments). These are prerequisites for the claim that FC reduces risk from undetected VBNC cells.
minor comments (2)
  1. [Abstract] Abstract: Grammar and phrasing issues include 'FC was capable to detect' (should be 'capable of detecting'), 'to decreasing the risk' (should be 'in decreasing the risk' or 'for decreasing'), and the awkward sentence 'showing that both mild temperatures would not be completely effective eliminating all bacteria but compromising their membranes'.
  2. [Abstract] Abstract: The temperature trends are described only qualitatively; quantitative values or a table summarizing percentages and absolute counts at each temperature would improve clarity.

Simulated Author's Rebuttal

2 responses · 0 unresolved

We thank the referee for their constructive comments on the need for quantitative details and methodological clarifications. We respond to each major comment below and indicate revisions where appropriate.

read point-by-point responses

  1. Referee: [Abstract] Abstract: The central claim that 'linear regression analysis showed good correlations between plate count results vs FC results' and that FC detects cells 'that cannot be detected with classical plate count methods' lacks any reported R² values, p-values, sample sizes, error bars, or data tables/figures. This information is load-bearing for evaluating whether the correlations support the superiority of FC over plate counts.

    Authors: The abstract summarizes the key finding, while the full results section presents the linear regression analysis with supporting figures showing the correlations at each temperature. To make this information immediately accessible, we will revise the abstract to explicitly report the R² values, p-values, and sample sizes from the regressions. Error bars from the replicate measurements are already shown in the figures. revision: yes

  2. Referee: [Abstract] Abstract/Methods (implied): No description is given of controls for food matrix effects, validation of the specific fluorescent dyes and gating strategy against heat-induced artifacts, or confirmation that membrane compromise detected by FC corresponds to viable but non-culturable states (e.g., via recovery experiments). These are prerequisites for the claim that FC reduces risk from undetected VBNC cells.

    Authors: We agree that the methods would benefit from expanded description. The experiments followed standard protocols for the commercial live/dead staining kit and used established gating based on fluorescence intensity thresholds; we will add explicit details on the gating strategy and any matrix controls performed with the PIF samples. However, the study did not include post-treatment recovery experiments to directly confirm VBNC status. We will therefore revise the discussion to qualify the interpretation as membrane-compromised cells that may include VBNC states, rather than asserting direct detection of VBNC cells, and adjust the risk-reduction claim accordingly. revision: partial

Circularity Check

0 steps flagged

No significant circularity

full rationale

This is a purely empirical methods-comparison paper. It reports direct experimental counts from flow cytometry (with standard dyes/gating) versus plate counts after heat treatments, plus a linear regression on the paired results. No equations, fitted parameters turned into predictions, ansatzes, uniqueness theorems, or self-citations appear in the provided text. The central claim (FC detects membrane-compromised cells missed by plating) is a straightforward empirical observation, not a derivation that reduces to its own inputs by construction.

Axiom & Free-Parameter Ledger

0 free parameters · 1 axioms · 0 invented entities

The paper rests on the domain assumption that flow-cytometry staining reports true physiological state; no free parameters, invented entities, or additional axioms are introduced.

axioms (1)
  • domain assumption Flow cytometry with membrane-integrity dyes accurately classifies cells as live, compromised, or dead after heat exposure in reconstituted formula.
    The entire comparison and safety conclusion depends on this standard but untested-in-this-matrix assumption.

pith-pipeline@v0.9.0 · 5769 in / 1216 out tokens · 26627 ms · 2026-05-25T18:02:40.995015+00:00 · methodology

discussion (0)

Sign in with ORCID, Apple, or X to comment. Anyone can read and Pith papers without signing in.

Reference graph

Works this paper leans on

5 extracted references · 5 canonical work pages

  1. [1]

    Enterobacteriaceae

    Modeling the Listeria innocua micropopulation lag phase and its variability. Int. J. Food Microbiol. 164, 60–69. https://doi.org/10.1016/j.ijfoodmicro.2013.03.003 Aguirre, J.S., Pin, C., Rodriguez, M.R., Garcia de Fernando, G.D., 2009. Analysis of the variability in the number of viable bacteria after mild heat treatment of food. Appl. Environ. Microbiol....

    work page doi:10.1016/j.ijfoodmicro.2013.03.003 2013

  2. [2]

    Resolution of viable and membrane-compromised bacteria in freshwater and marine waters based on analytical flow cytometry and nucleic acid double staining. Appl. Environ. Microbiol. 67, 4662–4670. https://doi.org/10.1128/AEM.67.10.4662-4670.2001 Gunasekera, T.S., Attfield, P. V., Veal, D.A., 2000. A flow cytometry method for rapid detection and enumeratio...

    work page doi:10.1128/aem.67.10.4662-4670.2001 2001

  3. [3]

    Survival of low-pH stress by Escherichia coli O157:H7: correlation between alterations in the cell envelope and increased acid tolerance

    https://doi.org/10.1099/ijs.0.65577-0 Jordan, K.N., Oxford, L., O’Byrne, C.P., 1999. Survival of low-pH stress by Escherichia coli O157:H7: correlation between alterations in the cell envelope and increased acid tolerance. Appl. Environ. Microbiol. 65, 3048–55. Joshi, S.S., Howell, A.B., D’Souza, D.H., 2014. Cronobacter sakazakii reduction by blueberry pr...

    work page doi:10.1099/ijs.0.65577-0 1999

  4. [4]

    Outbreak of necrotizing enterocolitis associated with Enterobacter sakazakii in powdered milk formula. J. Clin. Microbiol. 39, 293–297. https://doi.org/10.1128/JCM.39.1.293-297.2001 Virta, M., Lineri, S., Kankaanpää, P., Karp, M., Peltonen, K., Nuutila, J., Lilius, E.M.,

    work page doi:10.1128/jcm.39.1.293-297.2001 2001

  5. [5]

    Determination of complement-mediated killing of bacteria by viability staining and bioluminescence. Appl. Environ. Microbiol. 64, 515–9. Wagner, S., Snipes, W., 1982. Effects of acridine plus near-ultraviolet light on the outer membrane of Escherichia coli. Photochem. Photobiol. 36, 255–258. https://doi.org/10.1111/j.1751-1097.1982.tb04373.x Wesche, A.M.,...

    work page doi:10.1111/j.1751-1097.1982.tb04373.x 1982