| 1. |
- Budi Susilo, Yusak
(författare)
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Staphylococcus aureus toxins - Influence on food safety and animal health
- 2016
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Doktorsavhandling (övrigt vetenskapligt/konstnärligt)abstract
- Staphylococcus aureus (S. aureus) is a notorious opportunistic foodborne pathogen and also a common cause of bovine mastitis. It is known to produce many different virulence factors, including various staphylococcal enterotoxins and toxic shock syndrome toxin-1 (TSST-1). The aim of this work was to investigate the regulation, expression, formation and role of S. aureus toxins in relation to food safety and animal health. The link between the expression of the sea gene and the formation of enterotoxin A (SEA) and the life cycle of the sea-bearing Siphoviridae bacteriophages was investigated. Variations in SEA concentration between different strains of S. aureus were found to depend on the induction capacity of the phage, rather than sequence differences in the sea region. The SOS system, which responds to DNA damage in the cell, was also shown to be linked to the phage life cycle through the RecA protein. A novel method of monitoring SEA formation in real-time using flow cytometry was developed by fusing a green fluorescent protein (GFP) reporter to SEA. The mean value of the fluorescence intensity of the cells was shown to correspond to the SEA concentration determined by ELISA. This method was used to monitor SEA formation in the presence of different concentrations of NaCl, and has the potential to be further developed and optimized for rapid, large-scale screening of the effect of different environmental factors on toxin formation. The effect of sodium nitrite (NaNO2) on the expression of the sed gene and the formation of enterotoxin D (SED) was investigated in three different wild type S. aureus strains and their isogenic Agr, SarA and SigB regulatory mutants. The investigation revealed that SED is not as strongly dependent on the Agr system as previously reported. SED expression and formation were also measured in an Agr deletion mutant grown on boiled ham. The results showed significant differences in SED formation compared to growth in an optimal liquid broth, emphasizing the import¬ance of performing experiments on real food environment. The function of enterotoxin C (SEC) and TSST-1 in bovine mastitis was studied using an experimental model with bovine mammary epithelial cells. S. aureus SEC and TSST-1 deletion mutants showed significantly reduced infection capability compared to the isogenic wild type strains. This indicates that toxins may play a role during the establishment of infection, and should be further investigated. A deeper understanding of the regulation, formation and function of S. aureus toxins will help improve food safety and advance the development of prevention strategies and treatments for bovine mastitis in the future.
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| 2. |
- Schelin, Jenny, et al.
(författare)
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Expression of staphylococcal enterotoxins under stress encountered during food production and preservation
- 2017
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Ingår i: Toxins. - : MDPI AG. - 2072-6651. ; 9:12
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Forskningsöversikt (refereegranskat)abstract
- Staphylococcal food poisoning (SFP) is the most prevalent cause of food-borne intoxications worldwide. Consumption of enterotoxins preformed in food causes violent vomiting and can be fatal in children and the elderly. While being repressed by competing bacteria in most matrices, Staphylococcus aureus benefits from crucial competitive advantages in foods with high osmolarity or low pH. During recent years, the long-standing belief in the feasibility of assessing SFP risk based on colony-forming units of S. aureus present in food products has been disproven. Instead, researchers and food business operators are acutely aware of the imminent threat arising from unforeseeable enterotoxin production under stress conditions. This paradigm shift led to a variety of new publications enabling an improved understanding of enterotoxin expression under stress conditions encountered in food. The wealth of data provided by these studies is extremely diverse, as it is based on different methodological approaches, staphylococcal strains, stressors, and enterotoxins. Therefore, in this review, we aggregated and critically evaluated the complex findings of these studies, to provide readers with a current overview of the state of research in the field.
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| 3. |
- Sihto, Henna Maria, et al.
(författare)
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Effect of sodium nitrite and regulatory mutations Δagr, ΔsarA, and ΔsigB on the mRNA and protein levels of staphylococcal enterotoxin D
- 2016
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Ingår i: Food Control. - : Elsevier BV. - 0956-7135. ; 65, s. 37-45
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Tidskriftsartikel (refereegranskat)abstract
- Staphylococcal food poisoning results from ingestion of enterotoxins produced by Staphylococcus aureus. Staphylococcal enterotoxin D (SED) is one of the most common toxins detected in S. aureus strains associated with intoxications. The effect of sodium nitrite on enterotoxin production has been only partly investigated, despite its wide usage in meat products. In addition, the factors influencing SED regulation are unclear. The aim of this study was to determine the effect of sodium nitrite on sed transcription and SED production, as well as the effect of regulatory mutations on SED protein levels. Temporal sed mRNA and SED protein levels were compared in LB and LB supplemented with 150 mg/L nitrite, and SED protein levels between wild type (wt) and isogenic regulatory mutants (Δ. agr, Δ. sarA, Δ. sigB) under control and sodium nitrite conditions. Relative sed mRNA levels of wt strains were higher in late stationary phase in the presence of nitrite compared to control conditions. However, SED protein levels were decreased in the presence of nitrite. In LB, Δ. agr mutants showed SED levels similar to the wt, while Δ. sarA mutants exhibited reduced and Δ. sigB mutants increased SED levels compared to the wt. In LB with sodium nitrite, SED levels of mutant strains were reduced similar to the wt strains, except for two Δ. agr mutants, in which SED levels were increased in the presence of nitrite. Overall, strain-specific variation with regard to the effect of regulatory mutations was observed. In addition, the data suggests that SED regulation may not be as tightly dependent on Agr as previously described.
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| 4. |
- Susilo, Yusak Budi, et al.
(författare)
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Reduced enterotoxin D formation on boiled ham in staphylococcus aureus Δagr mutant
- 2017
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Ingår i: Toxins. - : MDPI AG. - 2072-6651. ; 9:9
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Tidskriftsartikel (refereegranskat)abstract
- Staphylococcal food poisoning (SFP) is a common cause of foodborne illness worldwide, and enterotoxin D (SED) is one of the most frequent Staphylococcus aureus enterotoxins associated with it. It has been reported that the expression and formation of SED in S. aureus is regulated by the quorum sensing Agr system. In this study, the effect of agr deletion on sed expression in S. aureus grown on boiled ham was investigated. Growth, sed mRNA and SED protein levels in an S. aureus wild type strain and its isogenic Δagr mutant were monitored for 14 days at 22 °C. The results showed that although deletion of the agr gene did not affect the growth rate or maximum cell density of S. aureus on boiled ham, it had a pronounced effect on SED formation during the first 5 days of incubation. The SED concentration was not reflected in the amount of preceding sed transcripts, suggesting that sed transcription levels may not always reflect SED formation. The expression of RNAIII transcript, the regulatory signal of the Agr system, was also monitored. Similar transcription patterns were observed for RNAIII and sed. Surprisingly, in the Δagr mutant, sed expression was comparable to that in the wild type strain, and was thus unaffected by deletion of the Agr system. These results demonstrate that the Agr system appears to only partially affect SED formation, even in a real food environment.
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| 5. |
- Zeaki, Nikoleta, et al.
(författare)
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Prophage-Encoded Staphylococcal Enterotoxin A: Regulation of Production in Staphylococcus aureus Strains Representing Different Sea Regions.
- 2015
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Ingår i: Toxins. - : MDPI AG. - 2072-6651. ; 7:12, s. 5359-5376
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Tidskriftsartikel (refereegranskat)abstract
- The present study investigates the nature of the link between the staphylococcal enterotoxin A (SEA) gene and the lifecycle of Siphoviridae bacteriophages, including the origin of strain variation regarding SEA production after prophage induction. Five strains representing three different genetic lines of the sea region were studied under optimal and prophage-induced growth conditions and the Siphoviridae lifecycle was followed through the phage replicative form copies and transcripts of the lysogenic repressor, cro. The role of SOS response on prophage induction was addressed through recA transcription in a recA-disruption mutant. Prophage induction was found to increase the abundance of the phage replicative form, the sea gene copies and transcripts and enhance SEA production. Sequence analysis of the sea regions revealed that observed strain variances were related to strain capacity for prophage induction, rather than sequence differences in the sea region. The impact of SOS response activation on the phage lifecycle was demonstrated by the absence of phage replicative form copies in the recA-disruption mutant after prophage induction. From this study it emerges that all aspects of SEA-producing strain, the Siphoviridae phage and the food environment must be considered when evaluating SEA-related hazards.
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