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Etter D, Jenni C, Tasara T, Johler S. Mild Lactic Acid Stress Causes Strain-Dependent Reduction in SEC Protein Levels. Microorganisms 2021; 9:1014. [PMID: 34066749 PMCID: PMC8151770 DOI: 10.3390/microorganisms9051014] [Citation(s) in RCA: 3] [Impact Index Per Article: 1.0] [Reference Citation Analysis] [Abstract] [Key Words] [Track Full Text] [Download PDF] [Figures] [Journal Information] [Subscribe] [Scholar Register] [Received: 03/24/2021] [Revised: 04/30/2021] [Accepted: 05/05/2021] [Indexed: 12/12/2022] Open
Abstract
Staphylococcal enterotoxin C (SEC) is a major cause of staphylococcal food poisoning in humans and plays a role in bovine mastitis. Staphylococcus aureus (S. aureus) benefits from a competitive growth advantage under stress conditions encountered in foods such as a low pH. Therefore, understanding the role of stressors such as lactic acid on SEC production is of pivotal relevance to food safety. However, stress-dependent cues and their effects on enterotoxin expression are still poorly understood. In this study, we used human and animal strains harboring different SEC variants in order to evaluate the influence of mild lactic acid stress (pH 6.0) on SEC expression both on transcriptional and translational level. Although only a modest decrease in sec mRNA levels was observed under lactic acid stress, protein levels showed a significant decrease in SEC levels for some strains. These findings indicate that post-transcriptional modifications can act in SEC expression under lactic acid stress.
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Affiliation(s)
- Danai Etter
- Institute for Food Safety and Hygiene, University of Zurich, 8057 Zurich, Switzerland; (D.E.); (T.T.)
- Laboratory of Food Microbiology, Institute for Food, Nutrition and Health (IFNH), ETH Zurich, 8092 Zurich, Switzerland;
| | - Céline Jenni
- Laboratory of Food Microbiology, Institute for Food, Nutrition and Health (IFNH), ETH Zurich, 8092 Zurich, Switzerland;
| | - Taurai Tasara
- Institute for Food Safety and Hygiene, University of Zurich, 8057 Zurich, Switzerland; (D.E.); (T.T.)
| | - Sophia Johler
- Institute for Food Safety and Hygiene, University of Zurich, 8057 Zurich, Switzerland; (D.E.); (T.T.)
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Zeaki N, Johler S, Skandamis PN, Schelin J. The Role of Regulatory Mechanisms and Environmental Parameters in Staphylococcal Food Poisoning and Resulting Challenges to Risk Assessment. Front Microbiol 2019; 10:1307. [PMID: 31244814 PMCID: PMC6581702 DOI: 10.3389/fmicb.2019.01307] [Citation(s) in RCA: 33] [Impact Index Per Article: 6.6] [Reference Citation Analysis] [Abstract] [Key Words] [Track Full Text] [Download PDF] [Figures] [Journal Information] [Subscribe] [Scholar Register] [Received: 12/06/2018] [Accepted: 05/27/2019] [Indexed: 11/29/2022] Open
Abstract
Prevention, prediction, control, and handling of bacterial foodborne diseases - an ongoing, serious, and costly concern worldwide - are continually facing a wide array of difficulties. Not the least due to that food matrices, highly variable and complex, can impact virulence expression in diverse and unpredictable ways. This review aims to present a comprehensive overview of challenges related to the presence of enterotoxigenic Staphylococcus aureus in the food production chain. It focuses on characteristics, expression, and regulation of the highly stable staphylococcal enterotoxins and in particular staphylococcal enterotoxin A (SEA). Together with the robustness of the pathogen under diverse environmental conditions and the range of possible entry routes into the food chain, this poses some of the biggest challenges in the control of SFP. Furthermore, the emergence of new enterotoxins, found to be connected with SFP, brings new questions around their regulatory mechanisms and expression in different food environments. The appearance of increasing amounts of antibiotic resistant strains found in food is also highlighted. Finally, potentials and limitations of implementing existing risk assessment models are discussed. Various quantitative microbial risk assessment approaches have attempted to quantify the growth of the bacterium and production of disease causing levels of toxin under various food chain and domestic food handling scenarios. This requires employment of predictive modeling tools, quantifying the spatiotemporal population dynamics of S. aureus in response to intrinsic and extrinsic food properties. In this context, the armory of predictive modeling employs both kinetic and probabilistic models to estimate the levels that potentiate toxin production, the time needed to reach that levels, and overall, the likelihood of toxin production. Following risk assessment, the main challenge to mitigate the risk of S. aureus intoxication is first to prevent growth of the organism and then to hamper the production of enterotoxins, or at least prevent the accumulation of high levels (e.g., >10-20 ng) in food. The necessity for continued studies indeed becomes apparent based on the challenges to understand, control, and predict enterotoxin production in relation to the food environment. Different types of food, preservatives, processing, and packaging conditions; regulatory networks; and different staphylococcal enterotoxin-producing S. aureus strains need to be further explored to obtain more complete knowledge about the virulence of this intriguing pathogen.
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Affiliation(s)
- Nikoleta Zeaki
- Division of Applied Microbiology, Department of Chemistry, Lund University, Lund, Sweden
| | - Sophia Johler
- Institute for Food Safety and Hygiene, University of Zurich, Zurich, Switzerland
| | - Panagiotis N. Skandamis
- Laboratory of Food Quality Control and Hygiene, Department of Food Science and Human Nutrition, Agricultural University of Athens, Athens, Greece
| | - Jenny Schelin
- Division of Applied Microbiology, Department of Chemistry, Lund University, Lund, Sweden
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Schelin J, Susilo YB, Johler S. Expression of Staphylococcal Enterotoxins under Stress Encountered during Food Production and Preservation. Toxins (Basel) 2017; 9:E401. [PMID: 29244757 PMCID: PMC5744121 DOI: 10.3390/toxins9120401] [Citation(s) in RCA: 32] [Impact Index Per Article: 4.6] [Reference Citation Analysis] [Abstract] [Key Words] [MESH Headings] [Track Full Text] [Download PDF] [Journal Information] [Subscribe] [Scholar Register] [Received: 11/19/2017] [Revised: 12/12/2017] [Accepted: 12/14/2017] [Indexed: 12/24/2022] Open
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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Affiliation(s)
- Jenny Schelin
- Applied Microbiology, Department of Chemistry, Lund University, SE-221 00 Lund, Sweden.
| | - Yusak Budi Susilo
- Applied Microbiology, Department of Chemistry, Lund University, SE-221 00 Lund, Sweden.
| | - Sophia Johler
- Institute for Food Safety and Hygiene, Vetsuisse Faculty University of Zurich, Winterthurerstrasse 272, 8057 Zurich, Switzerland.
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Fujikawa H, Nagaoka K, Arai K. Degradation of staphylococcal enterotoxin A by a Pseudomonas aeruginosa isolate from raw milk. Biosci Biotechnol Biochem 2017; 81:1436-1443. [PMID: 28417705 DOI: 10.1080/09168451.2017.1314755] [Citation(s) in RCA: 1] [Impact Index Per Article: 0.1] [Reference Citation Analysis] [Abstract] [Key Words] [Track Full Text] [Journal Information] [Subscribe] [Scholar Register] [Indexed: 10/19/2022]
Abstract
Recently, we found that staphylococcal enterotoxin A (SEA)-producing Staphylococcus aureus strains produced SEA in raw milk with microbial contaminants at high temperatures like 40 °C only. Moreover, the concentration of SEA produced in raw milk gradually decreased after the peak. The reason(s) for SEA degradation in raw milk was studied in this study. Degradation of SEA spiked in raw milk was observed at 40 °C, but not at 25 °C. A Pseudomonas aeruginosa isolate from raw milk degraded SEA spiked in broth at 40 °C. A sample partially purified with a chromatographic method from culture supernatant of the isolate degraded SEA. Two main proteolytic bands were observed in the sample by zymographic analysis with casein. These results suggested that the SEA in raw milk might be degraded by a protease(s) produced by the P. aeruginosa isolate. This finding might be the first report on SEA degradation by a proteolytic enzyme(s) derived from Pseudomonas bacteria to our knowledge.
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Affiliation(s)
- Hiroshi Fujikawa
- a Faculty of Agriculture, Laboratory of Veterinary Public Health , Tokyo University of Agriculture and Technology , Tokyo , Japan
| | - Kentaro Nagaoka
- b Faculty of Agriculture, Laboratory of Veterinary Physiology , Tokyo University of Agriculture and Technology , Tokyo , Japan
| | - Katsuhiko Arai
- c Faculty of Agriculture, Sderoprotein and Leather Research Institute , Tokyo University of Agriculture and Technology , Tokyo , Japan
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Growth behavior and temporal enterotoxin D expression of Staphylococcus aureus strains under glucose and lactic acid stress. Food Control 2016. [DOI: 10.1016/j.foodcont.2015.10.008] [Citation(s) in RCA: 13] [Impact Index Per Article: 1.6] [Reference Citation Analysis] [Track Full Text] [Journal Information] [Subscribe] [Scholar Register] [Indexed: 11/24/2022]
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Sihto HM, Tasara T, Stephan R, Johler S. Validation of reference genes for normalization of qPCR mRNA expression levels in Staphylococcus aureus exposed to osmotic and lactic acid stress conditions encountered during food production and preservation. FEMS Microbiol Lett 2014; 356:134-40. [PMID: 24893820 DOI: 10.1111/1574-6968.12491] [Citation(s) in RCA: 47] [Impact Index Per Article: 4.7] [Reference Citation Analysis] [Abstract] [Key Words] [Track Full Text] [Journal Information] [Subscribe] [Scholar Register] [Received: 05/13/2014] [Accepted: 05/30/2014] [Indexed: 12/01/2022] Open
Abstract
Staphylococcus aureus represents the most prevalent cause of food-borne intoxications worldwide. While being repressed by competing bacteria in most matrices, this pathogen exhibits crucial competitive advantages during growth at high salt concentrations or low pH, conditions frequently encountered in food production and preservation. We aimed to identify reference genes that could be used to normalize qPCR mRNA expression levels during growth of S. aureus in food-related osmotic (NaCl) and acidic (lactic acid) stress adaptation models. Expression stability of nine housekeeping genes was evaluated in full (LB) and nutrient-deficient (CYGP w/o glucose) medium under conditions of osmotic (4.5% NaCl) and acidic stress (lactic acid, pH 6.0) after 2-h exposure. Among the set of candidate reference genes investigated, rplD, rpoB,gyrB, and rho were most stably expressed in LB and thus represent the most suitable reference genes for normalization of qPCR data in osmotic or lactic acid stress models in a rich medium. Under nutrient-deficient conditions, expression of rho and rpoB was highly stable across all tested conditions. The presented comprehensive data on changes in expression of various S. aureus housekeeping genes under conditions of osmotic and lactic acid stress facilitate selection of reference genes for qPCR-based stress response models.
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Affiliation(s)
- Henna-Maria Sihto
- Institute for Food Safety and Hygiene, Vetsuisse Faculty University of Zurich, Zurich, Switzerland
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Schelin J, Wallin-Carlquist N, Cohn MT, Lindqvist R, Barker GC, Rådström P. The formation of Staphylococcus aureus enterotoxin in food environments and advances in risk assessment. Virulence 2011; 2:580-92. [PMID: 22030860 PMCID: PMC3260550 DOI: 10.4161/viru.2.6.18122] [Citation(s) in RCA: 208] [Impact Index Per Article: 16.0] [Reference Citation Analysis] [Abstract] [Key Words] [MESH Headings] [Grants] [Track Full Text] [Journal Information] [Subscribe] [Scholar Register] [Received: 06/30/2011] [Revised: 09/15/2011] [Accepted: 09/16/2011] [Indexed: 01/02/2023] Open
Abstract
The recent finding that the formation of staphylococcal enterotoxins in food is very different from that in cultures of pure Staphylococcus aureus sheds new light on, and brings into question, traditional microbial risk assessment methods based on planktonic liquid cultures. In fact, most bacteria in food appear to be associated with surfaces or tissues in various ways, and interaction with other bacteria through molecular signaling is prevalent. Nowadays it is well established that there are significant differences in the behavior of bacteria in the planktonic state and immobilized bacteria found in multicellular communities. Thus, in order to improve the production of high-quality, microbiologically safe food for human consumption, in situ data on enterotoxin formation in food environments are required to complement existing knowledge on the growth and survivability of S. aureus. This review focuses on enterotoxigenic S. aureus and describes recent findings related to enterotoxin formation in food environments, and ways in which risk assessment can take into account virulence behavior. An improved understanding of how environmental factors affect the expression of enterotoxins in foods will enable us to formulate new strategies for improved food safety.
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Affiliation(s)
- Jenny Schelin
- Applied Microbiology, Department of Chemistry, Lund University, Lund, Sweden.
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Cretenet M, Nouaille S, Thouin J, Rault L, Stenz L, François P, Hennekinne JA, Piot M, Maillard MB, Fauquant J, Loubière P, Le Loir Y, Even S. Staphylococcus aureus virulence and metabolism are dramatically affected by Lactococcus lactis in cheese matrix. ENVIRONMENTAL MICROBIOLOGY REPORTS 2011; 3:340-351. [PMID: 23761280 DOI: 10.1111/j.1758-2229.2010.00230.x] [Citation(s) in RCA: 45] [Impact Index Per Article: 3.5] [Reference Citation Analysis] [Abstract] [Track Full Text] [Subscribe] [Scholar Register] [Indexed: 06/02/2023]
Abstract
In complex environments such as cheeses, the lack of relevant information on the physiology and virulence expression of pathogenic bacteria and the impact of endogenous microbiota has hindered progress in risk assessment and control. Here, we investigated the behaviour of Staphylococcus aureus, a major foodborne pathogen, in a cheese matrix, either alone or in the presence of Lactococcus lactis, as a dominant species of cheese ecosystems. The dynamics of S. aureus was explored in situ by coupling a microbiological and, for the first time, a transcriptomic approach. Lactococcus lactis affected the carbohydrate and nitrogen metabolisms and the stress response of S. aureus by acidifying, proteolysing and decreasing the redox potential of the cheese matrix. Enterotoxin expression was positively or negatively modulated by both L. lactis and the cheese matrix itself, depending on the enterotoxin type. Among the main enterotoxins involved in staphylococcal food poisoning, sea expression was slightly favoured in the presence of L. lactis, whereas a strong repression of sec4 was observed in cheese matrix, even in the absence of L. lactis, and correlated with a reduced saeRS expression. Remarkably, the agr system was downregulated by the presence of L. lactis, in part because of the decrease in pH. This study highlights the intimate link between environment, metabolism and virulence, as illustrated by the influence of the cheese matrix context, including the presence of L. lactis, on two major virulence regulators, the agr system and saeRS.
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Affiliation(s)
- Marina Cretenet
- INRA, UMR1253 STLO, 85 rue de Saint Brieuc, F-35000 Rennes, France. Agrocampus Ouest, UMR1253 STLO, 85 rue de Saint Brieuc, F-35000 Rennes, France. Université de Toulouse; INSA, UPS, INP; LISBP, 135 Avenue de Rangueil, F-31077 Toulouse, France. INRA, UMR792 Ingénierie des Systèmes Biologiques et des Procédés, F-31400 Toulouse, France. CNRS, UMR5504, F-31400 Toulouse, France. Genomic Research Laboratory, University of Geneva Hospitals, Rue Gabrielle-Perret-Gentil, 4 CH-1211 Geneva 14, Switzerland. University Medical Center, Department of Microbiology and Molecular Medicine, CH-1211 Geneva 4, Switzerland. Laboratory for Study and Research on Quality of Food and on Food Processes, French Agency for Food Safety (AFSSA-lerqap), National and Community Reference Laboratory, 94704 Maisons-Alfort cedex, France
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Cretenet M, Even S, Le Loir Y. Unveiling Staphylococcus aureus enterotoxin production in dairy products: a review of recent advances to face new challenges. ACTA ACUST UNITED AC 2011. [DOI: 10.1007/s13594-011-0014-9] [Citation(s) in RCA: 59] [Impact Index Per Article: 4.5] [Reference Citation Analysis] [Track Full Text] [Journal Information] [Subscribe] [Scholar Register] [Indexed: 01/17/2023]
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10
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Wallin-Carlquist N, Cao R, Márta D, da Silva AS, Schelin J, Rådström P. Acetic acid increases the phage-encoded enterotoxin A expression in Staphylococcus aureus. BMC Microbiol 2010; 10:147. [PMID: 20487538 PMCID: PMC2891721 DOI: 10.1186/1471-2180-10-147] [Citation(s) in RCA: 43] [Impact Index Per Article: 3.1] [Reference Citation Analysis] [Abstract] [MESH Headings] [Track Full Text] [Download PDF] [Figures] [Journal Information] [Subscribe] [Scholar Register] [Received: 02/24/2010] [Accepted: 05/20/2010] [Indexed: 11/10/2022] Open
Abstract
BACKGROUND The effects of acetic acid, a common food preservative, on the bacteriophage-encoded enterotoxin A (SEA) expression and production in Staphylococcus aureus was investigated in pH-controlled batch cultures carried out at pH 7.0, 6.5, 6.0, 5.5, 5.0, and 4.5. Also, genomic analysis of S. aureus strains carrying sea was performed to map differences within the gene and in the temperate phage carrying sea. RESULTS The sea expression profile was similar from pH 7.0 to 5.5, with the relative expression peaking in the transition between exponential and stationary growth phase and falling during stationary phase. The levels of sea mRNA were below the detection limit at pH 5.0 and 4.5, confirmed by very low SEA levels at these pH values. The level of relative sea expression at pH 6.0 and 5.5 were nine and four times higher, respectively, in the transitional phase than in the exponential growth phase, compared to pH 7.0 and pH 6.5, where only a slight increase in relative expression in the transitional phase was observed. Furthermore, the increase in sea expression levels at pH 6.0 and 5.5 were observed to be linked to increased intracellular sea gene copy numbers and extracellular sea-containing phage copy numbers. The extracellular SEA levels increased over time, with highest levels produced at pH 6.0 in the four growth phases investigated. Using mitomycin C, it was verified that SEA was at least partially produced as a consequence of prophage induction of the sea-phage in the three S. aureus strains tested. Finally, genetic analysis of six S. aureus strains carrying the sea gene showed specific sea phage-groups and two versions of the sea gene that may explain the different sea expression and production levels observed in this study. CONCLUSIONS Our findings suggest that the increased sea expression in S. aureus caused by acetic acid induced the sea-encoding prophage, linking SEA production to the lifecycle of the phage.
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Affiliation(s)
| | - Rong Cao
- Applied Microbiology, Lund Institute of Technology, Lund University, Lund, Sweden
| | - Dóra Márta
- Applied Microbiology, Lund Institute of Technology, Lund University, Lund, Sweden
- Dept. of Microbiology and Biotechnology, Faculty of Food Science, Corvinus University of Budapest, Budapest, Hungary
| | - Ayla Sant'Ana da Silva
- Applied Microbiology, Lund Institute of Technology, Lund University, Lund, Sweden
- Dept. of Biochemistry, Chemistry Institute, Federal University of Rio de Janeiro, Rio de Janeiro, Brazil
| | - Jenny Schelin
- Applied Microbiology, Lund Institute of Technology, Lund University, Lund, Sweden
| | - Peter Rådström
- Applied Microbiology, Lund Institute of Technology, Lund University, Lund, Sweden
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Viedma PM, Abriouel H, Omar NB, López RL, Gálvez A. Antistaphylococcal effect of enterocin AS-48 in bakery ingredients of vegetable origin, alone and in combination with selected antimicrobials. J Food Sci 2010; 74:M384-9. [PMID: 19895485 DOI: 10.1111/j.1750-3841.2009.01288.x] [Citation(s) in RCA: 18] [Impact Index Per Article: 1.3] [Reference Citation Analysis] [Abstract] [Track Full Text] [Journal Information] [Subscribe] [Scholar Register] [Indexed: 11/29/2022]
Abstract
The inhibitory effect of enterocin AS-48 against Staphylococcus aureus was investigated in various types of bakery ingredients. Antibacterial activity greatly depended on the food substrate, ranging from complete inactivation of S. aureus in liquid caramel (in which the bacterium survived poorly) to no significant inhibition (as in vanilla or chocolate creams). Significant reductions of viable counts in the range of 1.8 to 2.7 log units (P < 0.05) were achieved in substrates like pumpkin confiture or diluted almond cream stored at temperatures of 10 or 22 degrees C. Given the very low activity detected in chocolate substrates, enterocin AS-48 was tested in combination with other antimicrobials. Bactericidal activity increased markedly for the combinations of AS-48 and 0.1% eugenol (v/v), 0.5% 2-nitropropanol (v/v), or 3% Nisaplin (w/v). Enterocin AS-48 could be applied in combination with other antimicrobials for preservation of bakery ingredients against S. aureus.
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Affiliation(s)
- Pilar Martinez Viedma
- Area de Microbiología, Depto de Ciencias de la Salud, Facultad de Ciencias Experimentales, Univ de Jaén, 23071-Jaén, Spain
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