Why is s. aureus halotolerant

However, staphylococci successfully overcome these challenges and can persist for extended periods in these environs. In clinical settings, staphylococci can remain viable on hands, in the air, in sterile solutions, on surfaces, on medical devices, and many more for extended durations allowing for their dissemination and transfer, which has greatly contributed to their prevalence and persistence in nosocomial infections and grossly undermines infection control strategies and affects patient outcomes.

As pathogens of significant public health concern, understanding the starvation-survival strategies that staphylococci employ in their persistence can aid in better clinical practices and the development of novel therapeutic strategies in combating staphylococcal infections.

The survival potential of staphylococci under several nutrient-limiting conditions has been investigated. Glucose is a major source of carbon for staphylococcal growth. These cells were smaller and exhibited increased resistance to certain stress conditions. The transition into glucose-starvation survival was accompanied by protein synthesis which was maintained into long-term starvation survival.

The role of these proteins included nutrient scavenging and recovery from starvation [ 70 ]. Another study investigating glucose-limitations on S.

Proteolysis of enzymes involved in several metabolic processes and pathways were observed as cells entered stationary phase as well as the uptake of the AA alanine and glycine. Proteins no longer required in nongrowing cells were degraded to supply and replenish nutrients required by starvation survivors [ 71 ].

Alterations in the intracellular concentrations of free AA were also observed in glucose starvation. Growing S. The uptake of lysine, histidine, cysteine, and aspartate, for example, increased substantially during starvation [ 72 ].

An abundance of AA is essential for protein biosynthesis for long-term survivability [ 62 ]. In general, S. Once intracellular, staphylococci also encounter host-mediated nutritional restrictions that limit the supply of critical substances from infection sites via a mechanism referred to as nutritional immunity [ 73 ]. Important nutrients include metals such as iron, manganese, and zinc, which are essential in a range of metabolic processes that facilitate staphylococcal growth and proliferation [ 74 ].

Neutrophils function to restrict staphylococcal access to these metals during infection via various mechanisms [ 75 ]. Bacterial siderophores such as staphyloferrin A and B, for example, compete with host systems to bind extracellular iron.

Siderophore-mediated iron acquisition is crucial for S. Using pore-forming toxins, S. Heme-binding proteins contribute to staphylococcal adhesion to host tissues and its resistance to innate immune processes [ 78 ]. Staphylococci have developed a repertoire of mechanisms that can detect, protect against, detoxify, and repair the effects of host oxidative stress [ 74 ].

Examples include the membrane-bound carotenoid pigment staphyloxanthin that gives S. Manganese is an important metal ion that is also involved in detoxification of ROS and also promotes intracellular virulence. Host phagocytic cells hinder the availability of manganese from engulfed bacteria by transporting it out of the phagosome or chelating it. To circumvent this action and fulfill its manganese requirement, S. To repair DNA damage owing to oxidative stress, the global SOS response system is activated and has proven highly effective in repairing damage caused by this and many other challenges [ 74 ].

This system has also been associated with staphylococcal virulence and resistance, and even the phenotypic switching of staphylococci during the DNA repair process [ 79 ]. Under controlled experimental conditions where bacteria are cultured in optimal, nonstress parameters, population homogeneity is the main mode of existence [ 29 ].

However, in the free-living natural environment where perturbations are the norm, bacteria can exist as a diverse, heterogeneous population [ 80 ]. Examples of population heterogeneity in staphylococci include the formation of phenotypic variants such as persister cells and small colony variants SCV. Both phenotypes share many similarities including their atypical metabolism, heightened tolerance to a range of terrestrial and host stressors, and involvement in many recalcitrant infections [ 19 , 81 ].

Staphylococcal persister cells were first described in the s in association with penicillin use, when a population of actively growing S.

Since that time, persister cells have been documented for many other bacteria exposed to different classes of antibiotics [ 81 , 83 ] and a range of other environmental conditions and hazards [ 83 — 85 ]. By definition, persister cells are a subpopulation of a genetically homogenous culture; they display phenotypic variations which enable them to tolerate and endure selective pressures that other members of the population are susceptible to [ 86 ].

In natural environments, these specialised survivor cells are thought to be preexisting through stochastic formation, as an evolutionary mechanism to maximize the survival fitness of the population under a wide variety of challenges [ 87 ]. Persister formation has also been attributed to a responsive mechanism where the bacteria respond to environmental cues by quantitatively and qualitatively modulating the rate at which their members undergo phenotypic conversion [ 84 ].

The mechanisms that facilitate phenotypic heterogeneity are epigenetic in nature, not involving changes in the underlying genome, thus allowing phenotypic reversibility in stress-free subculture. Understanding the underlying processes that enable phenotypic persistence is important to help improve treatment strategies, curb resistance development, and improve patient prognosis.

Staphylococcal persister cells display several metabolic characteristics that promote their survival and persistence in adverse environments. Classical descriptions of persister cells characterised them as dormant—metabolically inactive—but evidence shows that these cells remain active, albeit with minimal metabolic capacity that can maintain viability even for prolonged durations.

In this way, persister cells possess similarities with stationary-phase cells that also undergo arrested growth and replication, and can sustain this state for a long-term. Transition into a persister phenotype has been characterised by fluctuations in specialised persister proteins [ 88 ], a reduction of intracellular adenosine triphosphate ATP , and the expression of stationary-state markers [ 89 ].

When exposed to antibiotics that inhibit peptidoglycan synthesis, S. Persister cells maintained oxygen consumption in the presence of CW-active antibiotics although the rate was significantly reduced. These cultures also showed evidence of enzymatic activation related to lipid, protein, and saccharide metabolism [ 90 ]. These changes impact cellular processes including growth, cell division, and physiology [ 88 ]. Maintaining a level of metabolic activity during persister quiescence is pertinent to cellular integrity long-term and subsequent resuscitation and return to normal function when challenges abate.

Because persister phenotypic tolerance is unlike resistance which is genetically determined, persister characteristics were considered to be nonheritable by future progeny [ 91 ].

However, some studies have observed transmission of antibiotic tolerance to daughter cells maintained for several generations. This transgenerational plasticity is attributed to mechanisms of epigenetic inheritance [ 87 , 90 ]. The presence of persister phenotypes in clinical settings presents problematic implications. Their general downregulation of cellular activities greatly hampers the action of many chemotherapeutic agents that depend on active targets.

In fact, the heightened antibiotic tolerance associated with biofilm structures has been directly attributed to the presence of persister cells housed within. These cells can withstand prolonged and elevated concentrations of antibiotics that readily penetrate the biofilm core [ 86 ]. The transient nature of persisters allows them to regain a fully functional metabolism where they can replenish the population and reinitiate infections creating a cycle which can prove difficult to resolve [ 83 ].

These factors not only limit treatment options but also prolong treatment regimens which can subsequently promote the development of antibiotic resistant strains and further lead to treatment failure. Current research efforts are exploring the development of measures that address the persister lifestyle which includes preventing the transition of cells into quiescence, targeting the processes that facilitate resuscitation into a fully metabolic state, and the use of substances that awaken cellular targets for antimicrobial action [ 92 ].

Staphylococcal SCVs were first observed in the early 20th century and have gained reputation owing to their involvement in numerous recurrent nosocomial infections. They are a naturally occurring, slow-growing bacterial subpopulation which have been isolated under various conditions, and exhibit atypical morphological, ultrastructural, and biochemical properties in comparison to their corresponding wildtype WT that render them well-suited to long-term survival both terrestrially and intracellularly [ 93 ].

Metabolically, SCVs have been described as auxotrophs of haemin, menadione, and thymidine. Deficiencies in the production of these substances alter the electron transport chain ETC coupled with poor utilization of carbon sources and affect ATP production, resulting in slower growth rates, altered cell division, CW biosynthesis, AA transport and protein synthesis, decreased membrane potential, cationic and peptide transport, and carotenoid synthesis [ 94 — 96 ].

The alterations in morphology and biochemistry greatly impede accurate detection by conventional identification techniques which depend on these features, resulting in inaccurate diagnosis and treatment [ 93 ]. Similar to persister cells, SCVs are highly recalcitrant to many clinically important antibiotics not only because their altered metabolism reduces the efficacy of agents that depend on metabolically active targets, but also because SCV can also tolerate significantly elevated levels of many other antibiotics that do not depend on metabolic activity.

This severely limits therapeutic options and often results in a poor clinical outcome for patients [ 99 ]. The SCV phenotype is armed with a host of features that suitably adapt it to intracellular living.

Their decreased production in antigenic fragments masks their detection by host immune elements inhibiting rapid clearance and allowing their circulation from site to site.

Their downregulation of factors associated with WT virulence such as decreased toxin production has less cytotoxic damage on host cells and ensures a prolonged niche for their persistence [ , ]. Their increased expression of fibronectin-binding proteins, usually associated with cellular invasion, aids them adhere more to host cells and facilitate rapid internalisation.

Once internalised, SCVs withstand the milieu by upregulating protective mechanisms highly effective in maintaining viability [ , ]. An upregulated arginine-deiminase pathway, for example, compensates for defects in ATP production and counteracts the intracellular acidic environment [ 94 ]. Like persister cells, staphylococcal SCVs are also associated with biofilm structures.

Studies showed that SCV biofilms were generated much faster and were significantly thicker than their corresponding WT owing to upregulation of capsular polysaccharide synthesis [ ]. This structure is a crucial virulence factor particularly for CNS as it aids in their adherence and surface colonization in device-related infections [ ].

The combination of a SCV phenotype and hyperbiofilm formation results in a bacterial mass that is highly adept at adhering to and sustaining relapsing implant-related infections [ , ]. These are often difficult to resolve with chemotherapy and often require complete removal of the medical device to be resolved.

Because SCVs are phenotypically determined, their characteristics are transient and, thus, they are able to revert to their WT phenotype when conditions permit. The switch between phenotypes WT SCV contributes to resurgence of infections, even years after the initial incident. Overall, the SCV phenotype is a cost-effective strategy that enhances bacterial persistence in a range of conditions, and for pathogens like the staphylococci, having this phenotype as part of their lifestyle is highly advantageous [ ].

Staphylococci remain ubiquitous in the environment in spite of many conditions not propitious for their growth and proliferation. Their involvement in a wide spectrum of infections, some of which are difficult-to-treat, has earned them global recognition as one of the most notable pathogens of public health significance. Their remarkable survivability and persistence amidst the physicochemical pressures present both intracellularly and externally are made possible in part by their metabolic versatility—their ability to modulate their metabolic processes and composition to overcome challenges.

This attribute has contributed to their vast dissemination and resistance development, and highlights their problematic eradication in clinical settings. Adaptive metabolism in staphylococci appeared to be well-developed and a cost-effective strategy, attuned to ensure survival and competitiveness in a range of situations, both externally and intracellularly.

While some responses appeared to be similar across the staphylococci, others were unique to the particular strain. Commonly detected metabolite shifts were seen in AA, FA, and phospholipid content. In most cases reviewed, the synthesis of these adaptive metabolites increased under stress and functioned to help maintain homeostasis and enhance persistence in a challenge.

Some of these changes were manifested as physiological and ultrastructural modifications of target sites, for example, CW thickening, which appeared to be a more universal adaptive response to several challenges. It was also noted in some instances that adaptation to one stress conferred a cross-protection to another condition demonstrating cost-effectiveness. Other more advanced adaptations such as population heterogeneity involved broader transformations including the transition from normal growth to metabolic quiescence—modulation of processes and metabolites, in favour of only what was pertinent to staphylococcal survival, persistence, and subsequent resuscitation in that environment.

The ability of staphylococci to exist as subpopulations of phenotypic variants with heightened physiological tolerance and downregulated metabolic processes is also cost-effective, maximizing the fitness of the population and ensuring long-term survivability under a range of both bacteriostatic and bactericidal pressures.

This heterogeneity promotes their colonization of various niches, including those of the human host, and even alters the pathogenic profile to reflect their evolution, such as what is seen with SCV infections. Both persister and SCV phenotypes have proven problematic to eradicate and, when associated with pathogens like the staphylococci, these phenotypes enhance and complicate their public health impacts, particularly in the chronicity of infection and treatment failure. Variations in staphylococcal antibiotic susceptibility as a result of adaptive tolerance by both these phenotypes also prolong their presence in the environment where they can also acquire resistance genes and act as a reservoir for the dissemination of these genes, thereby promoting the development of antibiotic resistance in new niches even those devoid of antibiotics.

The study of adaptive metabolism in staphylococci is important in understanding staphylococcal behaviour and consequently developing approaches to target the strategies that render them problematic in various settings.

Future investigations in this field would include approaches that perturb staphylococcal transitions. Inhibiting the specific adaptive metabolites or the pathways that facilitate these metabolic shifts and phenotypic transformations provides a viable alternative that circumvents use of chemotherapeutics that promote the development of classical resistance mechanisms.

Since alterations in staphylococcal metabolism affect accurate diagnosis particularly where conventional tools that depend on a specified biochemistry are utilized as the first line of investigation and perhaps without additional confirmation, there is a need to develop novel tools that can rapidly detect altered metabolic states or atypical phenotypes to enable accurate and timely diagnosis and appropriate clinical intervention.

Through this review, it was noted that the majority of staphylococcal metabolic studies were understandably focused on S. However, there is a need to extend these investigations to encompass other members of the staphylococci that have also gained clinical prominence. CNS are increasingly involved in nosocomial infections particularly those associated with indwelling medical devices and biofilm. This approach would provide a more comprehensive understanding of combating staphylococcal infections.

Onyango and Mousa M. This is an open access article distributed under the Creative Commons Attribution License , which permits unrestricted use, distribution, and reproduction in any medium, provided the original work is properly cited. Article of the Year Award: Outstanding research contributions of , as selected by our Chief Editors.

Read the winning articles. Journal overview. Special Issues. Onyango 1 and Mousa M. Academic Editor: Chrissanthy Papadopoulou. Received 29 May Revised 28 Jul Accepted 12 Aug Published 20 Sep Abstract Staphylococci are highly successful at colonizing a variety of dynamic environments, both nonpathogenic and those of clinical importance, and comprise the list of pathogens of global public health significance.

Introduction Staphylococci are important microorganisms influencing ecosystems, industry, animal, and human health. Cell Envelope Modifications The staphylococcal cell can alter several of its features to help adapt to environmental challenge and maintain homeostasis. Temperature-Induced Modifications Adaptation to temperature changes is particularly crucial for staphylococci as they inhabit and circulate between many natural and man-made environments, several host species, varying anatomical sites, fomites, and food matrices, where they are susceptible to temperature fluctuations that can adversely impair the cell envelope and interfere with its intricate functions [ 16 , 17 ].

Osmotic Pressure Induced Modifications Staphylococci also display remarkable halotolerance in the presence of external osmotic pressure. Antibiotic-Induced Modifications Although the antibiotic era is only seven decades old, antibiotics have long existed in the natural environment and bacteria have developed mechanisms to circumvent their range of effects.

Other CE Modulations Cardiolipin CL , a membrane phospholipid, has been associated with bacterial adaptability to several stressors [ 57 ]. Cytoplasmic Modulations While the cell envelope provides significant protection and adaptability for the bacterium in the presence of external adversities, cytoplasmic-level modulations are also possible in the event of challenge and envelope compromise.

Temperature-Induced Changes S. Osmoprotection Halotolerant staphylococci can also adapt their cytoplasmic content to maintain osmotic pressure in the presence of a broad range of salt concentrations. Nutritional Adaptations Staphylococci also encounter numerous nutrient-limiting environments as they circulate between terrestrial habitats, clinical settings, and host species.

Population Adaptations Under controlled experimental conditions where bacteria are cultured in optimal, nonstress parameters, population homogeneity is the main mode of existence [ 29 ]. Persister Cells Staphylococcal persister cells were first described in the s in association with penicillin use, when a population of actively growing S. Small Colony Variants SCVs Staphylococcal SCVs were first observed in the early 20th century and have gained reputation owing to their involvement in numerous recurrent nosocomial infections.

Conclusion Staphylococci remain ubiquitous in the environment in spite of many conditions not propitious for their growth and proliferation. Conflicts of Interest The authors declare no conflicts of interest. References S. Nakamizo, G.

Egawa, T. Honda, S. Nakajima, Y. Belkaid, and K. View at: Google Scholar J. Huebner and D. Baron, Ed. View at: Google Scholar K. Crossley, K. Jefferson, G. Archer, and V. Fowler, Staphylococci in Human Disease , K. Crossley et al.

Kloos and T. Liebeke and M. Clements and S. Onyango, R. Dunstan, J. Gottfries, C. Von Eiff, and T. Alreshidi, R. However, linear regression analysis Fig. Besides initial concentration of LAB, the applied temperature also has a strong effect on the microbial growth dynamics.

With an increasing of the incubation temperature, the duration of pH and microbial lag phase is shortened. On the other hand, the higher the temperature, the higher the growth rates. The combined effect of temperature and the initial Fresco culture is depicted in Fig. From it, one is able to calculate the necessary addition of Fresco culture and thermal mode during milk or young cheese fermentation to ensure a minimal increase in the numbers of S. According to the EU regulation, the total S.

Similarly, also the culture A, which contains Lactobacillus acidophilus , was able to inhibit growth of S. Alomar et al. At an initial concentration of L.

Higher temperatures favoured the growth of S. Although acidification plays an important role in S. If pH and LAB play only a minor role in the inhibition, it can still be hypothesized that the cessation of the growth is due to the accumulation of antistaphylococcal substances produced by the LAB [ 77 ].

Results from literature suggest that S. On the other hand, inhibition of S. Indirect inhibitory effect may also be involved. The availability of nutrients may trigger other mechanisms, leading for instance to the secretion of metabolites, peptides or signalling molecules, which would in turn be responsible for the inhibitory effect of LAB [ 60 ]. Dependence of increase in S.

Fermentation of the lump cheese relies on native mesophilic lactic acid bacteria LAB such as Lactococcus lactis , Enterococcus faecalis , Lactobacillus casei , Lb.

During ripening, the essential role is played by the milk mould Geotrichum candidum and oxidative yeasts of the genera Torulopsis , Candida and Kluyveromyces [ 1 , 3 ]. Generally, cheeses are considered as one of the safest foods currently consumed. However, pathogenic bacteria which can be transmitted by dairy products cannot be underestimated.

Historically, there have been several outbreaks related to the consumption of cheeses. The predominantly responsible organisms Listeria monocytogenes , Escherichia coli , Salmonella spp. The sources of their contaminations were raw milk, inadequately pasteurized milk, or post-pasteurization contaminated milk [ 47 , 51 , 78 , 79 ]. In this context, microbiological specifications related to the finished cheeses made from raw milk defined by the Commission Regulation No.

They comprise of absence Salmonella spp. Despite the raw milk origin and substantial proportion of raw milk cheeses containing enterotoxigenic S. The safety and quality of fermented original cheeses manufactured from raw milk at a primary level is generally determined by various specific hygienic, technological, and intrinsic and extrinsic environmental factors.

The factors which contribute to the safety of cheeses with respect to pathogenic bacteria include milk quality, native lactic acid bacterial growth during cheese manufacture, pH, salt, environmental conditions and chemical changes during ripening. However, the most important role during fermentation is played by metabolism of the LAB participating in effective competition with pathogenic and spoilage microorganisms and subsequently in inhibition of undesirable microorganisms.

According to our investigations of eight products manufactured under upland farm conditions, the acidification of the curd started after a h period and went on intensively for 20 h. Thus, a level of acidity equivalent to pH of 5. Such a fairly long time permits to the growth not only LAB but also of undesirable bacteria, including S. Within these field trials, the initial numbers of S. The first 24 h of the process of making raw milk cheese appeared to be critical for S.

In cheeses with relatively slow acidification during the first 6 h, pH has no effect on the initial growth phase of S. High pH value in the fresh cheese suggests a weak lactose fermentation ability by the non-starter LAB [ 7 , 58 , 76 ]. In order to prevent S. As our previous experiments in model milk media confirmed, the Fresco culture is effective in the S. As seen in Fig. Such a short pH lag phase is crucial in pathogen growth inhibition during cheese manufacture, as has already been mentioned.

Higher diminution of pH during the first 6 hours of fermentation means lower S. The S. An increase in microbial counts in the first 24 h is a normal process in cheese making. This is partly due to the physical retention of microorganisms in the coagulum and also due to the microbial multiplication during coagulation and whey drainage [ 7 , 80 , 81 ].

In contrast to cheese without the addition Fresco starter, the S. Consumption of such a cheese might represent a potential threat of food poisoning outbreak if the enterotoxigenic strains are present. In order to keep the numbers of S. These initial counts would be accompanied with the suitable timing of pH decrease down to pH 5. The addition of an appropriate amount of mixed mesophilic LAB culture, which produces inhibitory substances, provides opportunities to add additional barriers to the growth of bacterial pathogens.

This assumption was also confirmed by some other authors. Olarte et al. In cheese without added starter culture, S. A rapid decrease in pH values from 6. From an initial average density of 1. In those cheeses S. Such acidic conditions contributed to the decrease in S. In raw milk cheeses collected by Jakobsen et al. The highest S. Nevertheless, none of the sample exceeded counts higher than 5 logs and so it was concluded that S. A correlation between the contamination level of the milk and contamination level of h old cheeses was noticed.

The initial S. During the ripening, the counts of S. During ripening of all 3 types of cheeses, pH was practically stable, reaching values in the range 5. The pH of fresh or ripened cheese was 6. On the other hand, in raw milk Mexican cheese Fresco, pH decline from pH 6.

Counts of S. It may be due to the S. Based on these results and observations from literature, it is strongly recommended, to use the starter culture at least in artisanal cheese production. Rapid fermentation process prevents against the growth of S. Even in mountain areas, this can be performed by the inoculation of LAB, e. Moreover, the addition of adjunct starter culture can improve flavour, reduced bitterness and increase the concentration of peptides, which impart desirable flavour, and of precursors of flavour volatiles [ 88 ].

But it has been suggested that positive results for flavour and texture development are strongly strain-dependent [ 85 ], so the selection of appropriate starter culture is necessary. The variation in the responses of S.

Similarly, many factors are known to influence the SEs production, e. NaCl content, water activity value, pH, temperature, atmosphere, amino acid composition and competing microflora. For that reason, it is crucial to understand which factors control enterotoxin production in raw milk cheese, in order to be able to assess their safety and to prevent staphylococcal food poisoning.

Even if pasteurization kills S. Besides this, pasteurization eliminates also enzymes and indigenous microflora, which are partly responsible for the development of the typical raw milk cheese flavour and texture [ 80 ].

Moreover, the raw milk contains a heat-labile lactoperoxidase system which has inhibitory effect to the growth of some pathogens [ 79 ]. The post-pasteurization addition of a starter culture may lead to losses in the unique organoleptic properties of the raw milk cheeses and to end products with uniform sensorial features [ 81 , 85 , 87 ]. Hence, there is today a renewed interest in traditionally produced raw milk cheeses due to consumer demands for increased varieties of cheese flavours and textures [ 80 ].

Consequently, as regards the safety of raw milk cheeses, potential pathogens associated with milk or milk products including Staphylococcus aureus , should still be of interest. The inhibitory potential of LAB on S. Taking into account the growth data obtained with a few S. Taking into account that the initial S. Artisanal raw milk cheese production poses a few critical factors limiting its safety. With reference to the growth of S.

Factors that may prevent the reaching of S. Inhibitory starters producing bacteriocins may also be used. Thus, the adding of a starter culture in artisanal cheese production is strongly recommended. Licensee IntechOpen. This chapter is distributed under the terms of the Creative Commons Attribution 3. Help us write another book on this subject and reach those readers. Login to your personal dashboard for more detailed statistics on your publications.

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Downloaded: Introduction The safety and quality of fermented raw foods are generally determined by the presence of pathogenic and spoilage microorganisms, their interaction with lactic acid bacteria, intrinsic, extrinsic and technological factors [ 1 ]. Resistance of S. Heat resistance D-values S. Acid tolerance Regarding pH, S. Salt resistance A characteristic feature that distinguishes S. Tolerance of S. Determination and identification of S. Determination of S. Identification of S.

Source of contamination and occurrence in the environment The natural ecological niches of S. Effect of incubation temperature on the S. Table 1. There are various ways by which cells can adapt to high-salt osmotic stress.

Considering that the response to osmotic stress consumes primary metabolites and energy, cells will use only the most appropriate pathway. Therefore, the contrasting patterns observed in some proteins in this study might be caused by shifts between coping strategies under different NaCl concentrations due to various reasons required to maintain a balance between effectiveness and economy.

Taken together, the activities of these proteins in cellular substance transport and amino acid metabolism play major roles in intracellular decomposition and amino acid synthesis for the protection S. Previous studies have shown that cells possess a self-protective mechanism against exposure to hyperosmotic environments that reduces unnecessary energy loss to help them focus on survival Lee et al.

In our study, alcohol dehydrogenase Adh was significantly downregulated by 0. Adh is closely associated with the cellular energy metabolism pathway, indicating that energy metabolism is likely affected by salt stress. It is well known that the tricarboxylic acid TCA cycle is the primary glycolytic pathway for glucose metabolism and that it plays a decisive role in organismal survival Mailloux et al.

In addition, 3-oxoacyl-[acyl-carrier-protein] synthase 2 FabF and malonyl CoA-acyl carrier protein transacylase FabD , which are involved in fatty acid biosynthesis and play prominent roles in transferring the malonyl moiety from coenzyme A to acyl-carrier protein, were upregulated after NaCl treatment Supplementary Tables S3 — S6. All of these results indicate that energy metabolism regulation contributes to the osmotic pressure tolerance analyzed in this study.

Studies have shown that osmotic stress may result in the production of a variety of stress proteins that function in cellular self-protection, nucleic acid repair, degradation of abnormal proteins, and regulation of intracellular and extracellular osmotic pressure Vilhelmsson and Miller, ; Kiran and Balaban, The DnaJ chaperone protein was downregulated by 0. DnaJ plays a central role in maintaining intracellular protein homeostasis and in improving cell membrane fluidity under osmotic stress conditions Sienczyk et al.

The proteins UreC and UreG were upregulated by 3. Increased expression of these four proteins, which are all ureases, contributes to the maintenance of homeostasis in S. As shown in Figure 10 , immunoglobulin-binding protein Sbi was downregulated by 0.

Burman et al. A previous study demonstrated that the Hlg proteins are broadly conserved among S. Alpha-hemolysin Hly was downregulated by 0. Hly is a potent cytotoxin and is closely linked to the pathogenesis of staphylococcal diseases Wilke and Bubeck Wardenburg, Staphyloxanthin biosynthesis protein CrtP was downregulated by 0.

Antonic et al. These results suggest that high NaCl concentrations reduce the expression levels of proteins related to pathogenic infections and virulence factors in S. We chose these modest cutoffs for two reasons.

Subsequent resequencing of its genome identified various variations SNPs and Indels in this strain data not shown that likely provide more efficient mechanisms for salt tolerance, and which do not change under different osmotic stress conditions.

Therefore, ZS01 may not need to extensively alter its gene transcription and protein expression levels to survive in high salt conditions. If we used the default cutoffs, few DEPs would have been identified in this study. Second, some important proteins, such as IcaB, SaeR and CspA, are known to play important roles in osmotic stress tolerance; however, their fold changes detected in this study were 0. Therefore, we decided that the common cutoff was not appropriate for this study, and we choose modest cutoff based on the specific characteristics of the S.

Because of the complexity of translation, some researchers have reported that the relative abundance of an mRNA and its corresponding protein may not show similar ratios among groups Maier et al. However, the trends in the changes in mRNA and protein levels are similar in most cases such that high protein levels likely result from both frequent transcription and high mRNA stability de Sousa Abreu et al.

In contrast, high osmotic stress downregulates the levels of proteins involved in biofilm formation and pathogenic infection. This study clarifies the mechanism of salt tolerance in S. All authors read and approved the final manuscript.

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