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. 2022 Apr 18:13:820067.
doi: 10.3389/fmicb.2022.820067. eCollection 2022.

Mild NaCl Stress Influences Staphylococcal Enterotoxin C Transcription in a Time-Dependent Manner and Reduces Protein Expression

Danai Etter  1   2 , Christina Ukowitz  1 , Corinne Eicher  1 , Taurai Tasara  1 , Sophia Johler  1
Affiliations

Mild NaCl Stress Influences Staphylococcal Enterotoxin C Transcription in a Time-Dependent Manner and Reduces Protein Expression

Danai Etter et al. Front Microbiol. .

Abstract

Enterotoxins (SEs) produced by Staphylococcus aureus are the cause of serious food intoxications. Staphylococcal enterotoxin C (SEC) is one of the main contributors, as it is often highly expressed. S. aureus possesses a competitive growth advantage over accompanying bacterial flora under stress conditions encountered in foods, such as high NaCl concentrations. However, the influence of NaCl as an external stressor on SEC expression is still unclear. We investigated the influence of 4.5% NaCl on sec mRNA and SEC protein levels. A qRT-PCR assay revealed that NaCl stress leads to time-dependently decreased or elevated sec mRNA levels for most strains. SEC protein levels were generally decreased under NaCl stress. Our findings suggest that NaCl stress lowers overall SEC concentration and time-dependently affects sec mRNA levels.

Keywords: SEC variants; food intoxication; stress response; superantigen; virulence gene regulation.

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Conflict of interest statement

The authors declare that the research was conducted in the absence of any commercial or financial relationships that could be construed as a potential conflict of interest.

Figures

Figure 1
Figure 1
Effect of NaCl stress on sec mRNA levels in seven S. aureus strains (BW10, NB6, SAI3, SAI48, SAR1, SAR38, OV20) measured by qRT-PCR. qPCR Δct values in exponential (4 h), early stationary (10 h), and late stationary phase (24 h) in LB and LB + 4.5% NaCl for each time point and strain. Control conditions in black and NaCl stress conditions in green. Target mRNA (sec) was normalized to two reference genes rho and rplD. Statistically significant changes in sec mRNA levels in LB + 4.5% NaCl compared to LB (p < 0.05) are marked by an asterisk.
Figure 2
Figure 2
Effect of NaCl stress on SEC protein expression in seven S. aureus strains (BW10, NB6, SAI3, SAI48, SAR1, SAR38, OV20) measured by ELISA. Protein concentration is shown in log10 values in exponential (4 h), early stationary (10 h), and late stationary phase (24 h) in LB and LB + 4.5% NaCl for each timepoint and strain. Control conditions in black and NaCl stress conditions in green. Statistically significant changes in SEC concentration in LB + 4.5% NaCl compared to LB (p < 0.05) are marked by an asterisk.
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