Access to this full-text is provided by Springer Nature.
Content available from Scientific Reports
This content is subject to copyright. Terms and conditions apply.
1
ScieNTific RepoRTS | (2018) 8:1732 | DOI:10.1038/s41598-017-18618-x
www.nature.com/scientificreports
Antimicrobial activity of apple cider
vinegar against Escherichia coli,
Staphylococcus aureus and Candida
albicans; downregulating cytokine
and microbial protein expression
Darshna Yagnik, Vlad Seran & Ajit J. Shah
The global escalation in antibiotic resistance cases means alternative antimicrobials are essential. The
aim of this study was to investigate the antimicrobial capacity of apple cider vinegar (ACV) against E.
coli, S. aureus and C. albicans. The minimum dilution of ACV required for growth inhibition varied for
each microbial species. For C. albicans, a 1/2 ACV had the strongest eect, S. aureus, a 1/25 dilution
ACV was required, whereas for E-coli cultures, a 1/50 ACV dilution was required (p < 0.05). Monocyte
co-culture with microbes alongside ACV resulted in dose dependent downregulation of inammatory
cytokines (TNFα, IL-6). Results are expressed as percentage decreases in cytokine secretion comparing
ACV treated with non-ACV treated monocytes cultured with E-coli (TNFα, 99.2%; IL-6, 98%), S. aureus
(TNFα, 90%; IL-6, 83%) and C. albicans (TNFα, 83.3%; IL-6, 90.1%) respectively. Proteomic analyses
of microbes demonstrated that ACV impaired cell integrity, organelles and protein expression. ACV
treatment resulted in an absence in expression of DNA starvation protein, citrate synthase, isocitrate
and malate dehydrogenases in E-coli; chaperone protein DNak and ftsz in S. aureus and pyruvate
kinase, 6-phosphogluconate dehydrogenase, fructose bisphosphate were among the enzymes absent
in C.albican cultures. The results demonstrate ACV has multiple antimicrobial potential with clinical
therapeutic implications.
Antibiotic resistance is rapidly becoming a major worldwide problem. There has been a steady increase in
the number of pathogens that show multiple drug resistance. In fact the World Health Organization predicts
that infections involving antibiotic resistant pathogens will pose major patient care management issues in the
future1.is will inevitably lead to an increase in hospital stays, cost, patient morbidity and mortality. In the
immunocompromised and at risk patients severe microbial infections can result in sepsis. Sepsis can rapidly
lead to systemic inammation and organ failure2. In response to microbial invasion, the innate immune sys-
tem reacts by triggering tissue damage. Mononuclear cells recognize pathogens associated with molecular pat-
terns (PAMPs) present on the microbial surface. is results in intracellular signaling cascades which initiate
pro-inammatory cytokine and chemokine release into the blood circulation. Unchecked, the chemokines will
continue to recruit more immune cells to the site of infection which release further pro-inammatory cytokines
enhancing inammation in a continuous feedback loop3. Essentially, antibiotics are antimicrobials but can also
act as immune modulators reducing the release of pro-inammatory cytokines such as IL-1β, IL-6, TNFα, IL-8,
and interferon-gamma (INF-gamma). Antibiotics can also aect mononuclear phagocytic function and modu-
late the activity of nuclear transcription factors such as NF-ĸB and activator proteins4–7. Microorganisms such as
E-coli, S. aureus and C. albicans form part of the human microbiota. However pathogenic forms of these microbes
have been implicated in blood or urinary tract infections, gastroenterititis, endocarditis, so tissue infections and
organ malfunction8–10.
Department of Natural Sciences, School of Science and Technology, Middlesex University, The Burroughs, London,
NW4 4BT, England, United Kingdom. Correspondence and requests for materials should be addressed to D.Y. (email:
d.yagnik@mdx.ac.uk)
Received: 18 August 2017
Accepted: 14 December 2017
Published: xx xx xxxx
OPEN
Content courtesy of Springer Nature, terms of use apply. Rights reserved
www.nature.com/scientificreports/
2
ScieNTific RepoRTS | (2018) 8:1732 | DOI:10.1038/s41598-017-18618-x
e anti-microbial agents used to treat gram negative infections such as β-lactams, uroquinolones, sul-
famethaoxathoxazole and trimethroprin are becoming increasingly ineective. Strains of S. aureus have emerged
with reduced susceptibility to vancomycin and methicillin6,11,12. Furthermore, antibiotic action itself can be prob-
lematic in terms of cell membrane permeability, intracellular inactivation and the inability to reach intracellular
structures in which organisms can hide. Alternative supplementation that can combat a plethora of microbes
without concurrent side eects would be of signicant healthcare interest as the discovery of eective new antibi-
otic has been slow but should be a global priority.
e Old Testament and Hippocrates reported on the use of ACV in combination with honey to combat infec-
tion and protect open skin wounds. Historically, vinegar has been produced and sold as a commercial commodity
for over 5000 years. In fact up until the sixth century BC, the Babylonians were making vinegars for consumption
as well as for use in healing13. Vinegar is the resultant product when ethyl alcohol is converted to acetic acid by
Acetobacter. It can be produced by dierent methods and a variety of raw materials such as wine, malted barley,
alcohol, fruits and cider14. ACV is produced from cider that has undergone acetous bioconversion and has rela-
tively low acidity (5% acetic acid). It also contains organic acids, avonoids, polyphenols, vitamins and minerals15.
ACV has been hailed as a supplement aiding weight loss, hyperlipademia, hypercholesterliaemia, nutritional
support, antioxidant defence and lowering blood pressure. Utilising organic acids as nutritional supplements
has been regarded as safe and can eliminate harmful intestinal bacteria16–18. e positive impact of dietary ACV
supplementation has been highlighted in vivo. ACV decreased the serum lipid prole in mice fed a high choles-
terol diet over 28 days. Intragrastric ACV addition induced a protective eect against erythrocyte, kidney and
liver oxidative injury as well as lowering cholesterol levels16. ACV also decreased blood triglyceride and very low
density lipoprotein levels in rats which had induced cholesterol induced hepatic steatosis18. Despite the known
health benets of dietary organic acid supplementation, to the best of our knowledge the direct eect of ACV on
microbes and mononuclear leucocytes has not been examined. e aim of the present study was to investigate the
antimicrobial activity of ACV on microbes and associated inammatory pathways.
Results
The antibacterial and antifungal activity of ACV against E. coli, S. aureus and C. albicans. In
order to determine the anti-microbial activity of ACV, E. coli, S. aureus and C. albicans were directly cultured
with dierent concentrations of ACV. Figure1 represents the experimental results. e minimum dose required
to restrict growth for C. albicans was neat, undiluted ACV (5% acidity), for S. aureus it was a 1/2 dilution (2.5%
acidity) and for E-coli, growth was restricted at a signicantly lower dilution of 1/50 (equivalent to 0.1% acidity).
We also measured the equivalent zones of inhibition (in mm) for each of the microbes at varying dilutions of
ACV which is depicted in the photographs of the culture plates (Fig.2). To translate the MIC into supplementary
Figure 1. Eect of varying concentrations of ACV on microbial growth aer incubation at 37 °C for 24 h. (a)
S. aureus; (b) C. albicans, (c) E-coli (d) E-coli. ACV was either applied neat or diluted 1:2 or 1:10 v/v in distilled
water. Zones of microbial growth inhibition are indicated by clear zones and vary with ACV dilutions for each
microbe. Photographs were taken using a 20 Mega pixel Samsung camera.
Content courtesy of Springer Nature, terms of use apply. Rights reserved
www.nature.com/scientificreports/
3
ScieNTific RepoRTS | (2018) 8:1732 | DOI:10.1038/s41598-017-18618-x
tablet dosages required, we tested concentration ranges from 400 µg/ml in doubling microdilutions to the lowest
of 3.1 µg/ml against each microbe. e MIC for ACV tablets at which no growth was visible was 62 µg/ml for E.
coli; 125 µg/ml for S. aureus and 250 µg/ml for C. albicans respectively. Both sets of results were also conrmed
further by microdilution. We used the Braggs ACV for all future experiments at the minimum inhibitory dilution
required for each organism.
Downregulation of pro-inammatory cytokine secretion by ACV in monocytes exposed to
microbes. e microbes utilised in our study have been extensively studied and are known to cause inam-
mation through their capacity to stimulate the leucocyte pro-inammatory cytokine cascades19,20. Hence, we
proceeded to measure mononuclear derived TNF-α and IL-6 cytokines as indicators of inammation which are
also the markers of choice for clinical diagnosis of septic infections21.
Figure3 depicts the eects of a dose dependent reduction in TNFα and IL-6 release from monocytes which
have been co-cultured with ACV, together with either C. albicans, E-coli or S. aureus for 24 h.
Consistent with the microbial growth inhibition data depicted in Fig.2, the eect of ACV at the minimum
inhibitory concentration of 1/50 resulted in a signicant reduction in monocyte derived TNFα (p = 0.008) and
IL-6 release (P = 0.001) in monocytes cultured with E-coli. For S. aureus the minimum inhibitory concentration
for ACV was found to be 1/10 in terms of reduction of TNFα (p = 0.011) and IL-6 (p = 0.03). For C.albicans the
minimum inhibitory dilution was lower at 1/2 dilution, for TNFα (p = 0.003) and IL-6 (p = 0.008). It was imper-
ative to ascertain whether the monocytes were alive during inoculation with the various microbes especially
aer incubation for 24 h at 37 °C. We added Trypan blue directly to monocytes which had been co-cultured with
microbes aer 2, 6 and 24 h. Light microscopy revealed that greater than 90% of cells were alive aer 24 h in all
co-cultures as demonstrated in (Fig.4a,b,c) which represents the light microscopic images of monocytes and the
microbes in co-cultures.
Upregulation of phagocytic capacity. We also investigated whether ACV could have an eect on the
phagocytic function of monocytes alone and also aer a 4 h exposure to microbes with or without ACV treat-
ment. A 14.2, 13.7 and 20.4% increase in monocyte phagocytic capacity was observed aer E. coli, S. aureus and
C. albicans co-culture with ACV respectively and in comparison to the resting unstimulated monocytes. Results
are expressed as the mean and SD of 3 similar experiments (Table1). is suggests that ACV can increase phago-
cytic potential in monocytes which is signicant as microbial phagocytosis is a key eector function of innate
immunity22.
Figure 2. Inhibition of microbe growth by ACV aer incubation for 24 h at 37 °C. (a) E-coli; (b) S. aureus (c)
C. albicans. Zone of inhibition was measured in mm. ese experiments represent data from three repeats.
EC = E-coli, SA = S. aureus, CA = C. albicans, ACV = Apple cider vinegar.
Content courtesy of Springer Nature, terms of use apply. Rights reserved
www.nature.com/scientificreports/
4
ScieNTific RepoRTS | (2018) 8:1732 | DOI:10.1038/s41598-017-18618-x
Proteomic results of E. coli, S. aureus and C. albicans after exposure to ACV. e bottom-up
proteomic study of ACV treated E-coli cultures revealed the absence in detection of key enzymes; citrate synthase,
isocitrate dehydrogenase, deoxyribose–phosphate idolase, malate dehydrogenase, aminomethyltransferase and
formate acetyltransferasesuccinyl-CoA ligase (Table2). An absence in acyl carrier protein, DNA protein includ-
ing DNA protection during starvation protein, integration host factor subunit alpha and ribosome associated
inhibitor A was evident. Following ACV treatment S. aureus cultures failed to express 50 s ribosomal proteins L2,
L15, L23, L24, enzymes; alcohol dehydrogenase, catalase, formate acetyltransferase, L-lactate dehydrogenase-2,
ornithine aminotransferase and serine hydroxymethyl transferase (Table3). Cell division protein ftsZ and
chaperone protein Dnak were also not detected. However an important pentose phosphate pathway enzyme:
6 phosphogluconate dehydrogenase decarboxylating was displayed. Table4 demonstrates that key enzymes
required for glycolysis and candida immunogenicity were undetected aer 24 h of exposure to ACV in C. albi-
cans. ese incorporated fructose bisphosphate aldolase, phosphogluconate dehydrogenase, pyruvate kinase and
peptidyl-propyl cis-trans isomerase.
Discussion
ACV has multiple antimicrobial properties on dierent microbial species, aecting microbe growth, suppressing
mononuclear cytokine and phagocytic responses. e tandem mass spectroscopy results are in cohesion with
Figure 3. Eect of ACV on pro-inammatory cytokine secretion from human monocytes infected with (a)
E-coli; (b) C. albicans and (c) S. aureus aer incubation for 24 h at 37 °C. ACV was added at dilutions of 1/10,
1/25, 1/50, 1/100 or 1/1000. EC = E-coli, SA = S. aureus, CA = C. albicans. e minimum inhibitory dilution
of ACV required for signicant pro-inammatory downregulation varied with each microbe. For TNFα, a
1/50 ACV minimum inhibitory dilution was required for EC, p = 0.0008; 1/10 for SA, p = 0.01; 1/2 for CA,
p = 0.0003 respectively. For IL-6, 1/50 ACV dilution was required for EC, p = 0.0008; 1/10 for SA, p = 0.03;
1/2 for CA, p = 0.008 respectively. Results represented are mean +/− SD of 3 experiments. We used student’s
paired t-tests for statistical evaluation (Excel 2017) with statistical signicance taken when p < 0.05. EC = E-coli,
SA = S. aureus, CA = C. albicans, ACV = Apple cider vinegar.
Content courtesy of Springer Nature, terms of use apply. Rights reserved
www.nature.com/scientificreports/
5
ScieNTific RepoRTS | (2018) 8:1732 | DOI:10.1038/s41598-017-18618-x
these observations. e microbes underwent signicant impairment following ACV addition which damaged cell
integrity, structural and metabolic proteins as well as nuclear material. Indeed the enzymes citrate synthase, isoc-
itrate dehydrogenase, malate dehydrogenase, aminomethyltransferase and formate acetyltransferasesuccinyl-CoA
ligase are crucial for E-coli growth, gene regulation and central, intracellular carbon metabolism. An absence of
these enzymes would aect glycolytic, tricarboxylic acid cycle, pentose phosphate, glycoxlate shunt and oxidative
phosphorylation pathways in E. coli23. Furthermore, the absence of DNA binding protein from starved cells, is
signicant as it protects E-coli and functions to control gene regulation during cell starvation24. With respect to
other proteins, we observed the presence of ribosomal proteins (L1, L6 and 30 s ribosomal proteins (S1, S4, S6,
Figure 4. (a–c) Photos of monocytes in co-culture with microbes. Monocytes were cultured with the microbes
and ACV. Trypan blue addition indicated over 95% viability. Red arrows indicate microbes and the blue arrow
shows monocytes in Fig.4a which are not visible in Fig.4b and c since they have been covered by the microbes.
Photographs were taken aer 24 h incubation at 37 °C under × 100 magnication using a light microscope
indicated over 90% viability with monocytes at 2, 4, 6 and 24 h of co-culture (24 h photos shown). A = C.
albicans, B = E-coli and C = S. aureus respectively.
Content courtesy of Springer Nature, terms of use apply. Rights reserved
www.nature.com/scientificreports/
6
ScieNTific RepoRTS | (2018) 8:1732 | DOI:10.1038/s41598-017-18618-x
Monocyte co-culture
conditions
Monocyte phagocytic capacity
expressed as % change increase in side
scatter. (mean ± SD)
Medium 6.1 ± 1.4
E-coli 9.0 ± 2.4
S. aureus 22.3 ± 2.2
C albicans 31.9 ± 2.4
E-coli + ACV 23.2 ± 3.7
S. aureus + AC V 36.0 ± 5.2
C albicans + AC V 52.3 ± 4.1
Table 1. Eect of ACV on human monocyte phagocytic capacity. In vitro dierentiated monocytes were
incubated with microbes for 4 h at 37 °C. Cells cultured with microbes with or without ACV were washed and
processed for detection on the Beckton Dickinson ow cytometer. An analysis of changes in regional gated
proles and % shi in side scatter was measured. Data is presented as mean ± SD of 3 similar experiments.
Protein Name Mass
(Da) Control E-coli
culture ACV Treated
E-coli culture
30S ribosomal protein S1 —*
30S ribosomal protein S11 13950 *
30S ribosomal protein S4 23512 *
30S ribosomal protein S6 15177 *
30S ribosomal protein S7 17593 *
30S ribosomal protein S8 14175 *
50S ribosomal protein 14923 * *
50S ribosomal protein L1 24714 *
50S ribosomal protein L17 14413 * *
50S ribosomal protein L2 29956 *
50S ribosomal protein L6 18949 *
60 kDa chaperonin 57464 * *
Acyl carrier protein 8693 *
Aminomethyltransferase 40235 *
Autonomous glycyl radical cofactor —*
Citrate synthase 48383 *
Cytidine deaminase 31805 *
Deoxyribose-phosphate aldolase 27958 *
DNA protection during starvation protein 18684 *
DNA-binding protein H-NS 15587 *
DNA-binding protein HU-alpha 9529 *
DNA-binding protein HU-beta 9220 *
Elongation factor Tu 1 43427 * *
Enolase 45683 * *
Formate acetyltransferase 1 85588 *
Glutamate/aspartate periplasmic-binding protein 33513 *
Glyceraldehyde-3-phosphate dehydrogenase 35681 * *
Integration host factor subunit alpha 11347 *
Isocitrate dehydrogenase [NADP] 46070 *
Major outer membrane lipoprotein Lpp 8375 *
Malate dehydrogenase 32488 *
Outer membrane protein A 37292 * *
Ribosome-associated inhibitor A 12777 *
Succinate dehydrogenase avoprotein subunit 65008 * *
Succinyl-CoA ligase [ADP-forming] subunit beta 42244 *
Transaldolase B 35368 *
Uridine phosphorylase 27313 * *
Table 2. List of E-coli proteins identied following ACV treatment. E-coli were cultured with 1/50 dilution of
ACV or alone in broth for 24 hours at 37 °C in a shaking incubator. Aer which mass spectroscopy analysis
was carried out. e “*” indicates the presence of protein whilst the blank region denotes no detection of that
particular protein.
Content courtesy of Springer Nature, terms of use apply. Rights reserved
www.nature.com/scientificreports/
7
ScieNTific RepoRTS | (2018) 8:1732 | DOI:10.1038/s41598-017-18618-x
S7, S8, S11) in ACV treated E. coli compared to control E. coli. ese are mostly RNA binding proteins hence
their presence could have been due to partial disintegration of 50 s and 30 s ribosomal breakdown whereas these
subunits might remain intact in untreated E. coli cultures. e absence of ribosome associated inhibitor A could
Protein name Mass
(Da)
Control
S. aureus
culture
ACV-
Tre ate d
S. aureus
culture
30S ribosomal protein S1 43250 * *
30S ribosomal protein S12 15334 *
30S ribosomal protein S2 29133 *
30S ribosomal protein S3 24085 * *
30S ribosomal protein S4 22999 *
30S ribosomal protein S5 17732 *
30S ribosomal protein S6 11588 *
30S ribosomal protein S7 17783 * *
30S ribosomal protein S8 14822 *
50S ribosomal protein L1 24693 *
50S ribosomal protein L13 16323 * *
50S ribosomal protein L14 13241 * *
50S ribosomal protein L15 15587 *
50S ribosomal protein L2 30194 *
50S ribosomal protein L21 11326 * *
50S ribosomal protein L23 10599 *
50S ribosomal protein L24 11529 *
50S ribosomal protein L25 23773 * *
50S ribosomal protein L29 8085 *
50S ribosomal protein L4 22451 * *
50S ribosomal protein L6 19774 *
6-phosphogluconate
dehydrogenase, decarboxylating 51941 *
Alcohol dehydrogenase 36424 *
Arginine deiminase 47113 * *
Bacterial non-heme ferritin 23773 * *
Catalase 58457 *
Cell division protein FtsZ 41012 *
Chaperone protein DnaK 66338 *
DNA-binding protein HU 9620 * *
Elongation factor Tu 43134 * *
Enolase 47145 * *
ESAT-6 secretion system
extracellular protein A 11029 *
Formate acetyltransferase 85264 *
Fructose-bisphosphate aldolase
class 1 32907 *
Isocitrate dehydrogenase [NADP] 46451 *
L-lactate dehydrogenase 2 34468 *
Ornithine aminotransferase 2 43675 *
Ornithine carbamoyltransferase,
catabolic 37853 * *
Probable malate:quinone
oxidoreductase 56135 * *
Putative universal stress protein
SA1532 18521 * *
Pyruvate dehydrogenase E1
component subunit beta 35194 * *
Serine hydroxymethyltransferase 45384 *
Table 3. List of S. aureus proteins identied following ACV treatment. S. aureus were cultured with 1/10
dilution of ACV or alone in broth for 24 hours at 37 °C in a shaking incubator. Aer which mass spectroscopy
analysis was carried out. e “*” indicates the presence of protein whilst the blank region denotes no detection
of that particular protein.
Content courtesy of Springer Nature, terms of use apply. Rights reserved
www.nature.com/scientificreports/
8
ScieNTific RepoRTS | (2018) 8:1732 | DOI:10.1038/s41598-017-18618-x
interrupt E. coli growth cycles as it serves to minimise translational errors25. Collectively these results support
the cytotoxic eects of ACV we observed on E-coli. ACV treated S. aureus cultures did not express the chap-
erone protein Dnak and the cell division protein sz. is is signicant as previous studies have shown that a
non-functional DnaK system can cause a reduced tolerance to heat, oxidative, antibiotic stresses and lowered
carotenoid production26. ere was also an absence of gateway enzymes involved in multiple pathways such as
ornithine aminotransferase27. 6 phosphogluconate dehydrogenase decarboxylating was expressed which is not
surprising as it plays a critical role in protecting cells from oxidative stress28. e eect of ACV on C.albican pro-
tein moieties was less dramatic, nevertheless we did detect the absence of key enzymes which are fundamental in
maintaining cell integrity and biosynthetic pathways29.
ere could be a strong possibility that ACV acts like other anti-pathogenic compounds in diverting mono-
cyte responses through toll receptor signalling pathways. ere is evidence that E-coli in particular can induce
a typical M1 monocyte prole through mechanisms involving NF-kB activation. is results in upregulation of
inammatory cytokines TNF-α and PI3 kinase stimulation30. e in vitro M1 monocyte phenotype is also prom-
inent in severe sepsis. is was shown in a study using baboons where a substantial mortality rate correlated with
high serum levels of TNFα and IL-6 following induced sepsis infection31. Unchecked high levels of circulating
M1 cytokines can rapidly lead to cardiac arrest and death hence any factor capable of lowering pro-inammatory
cytokine concentrations is essential in therapy32. It has been reported that ACV consists of acetic acid, avo-
noids such as gallic acid, tyrosol catechin, epicatechin, benzoic acid, vaninilin, caaric acid, coutaric acid, caf-
feic acid, acid and ferrulic acid ese constituents have been reported to aect immune defence and oxidative
responses18,33.
Furthermore, the mechanism of ACV activity could be attributed in part to the apple polyphenol content. Yang
et al. (2010) reported on the cellular protective eects of apple polyphenols on induced liver damage whereby
histopathological tissue destruction was limited and liver activity maintained in mice that received the polyphe-
nols34. e mechanisms involved were free radical scavenger action, lipid peroxidation modulation and the anti-
oxidant upregulation capacity of ACV. Interestingly, a study by Denis et al. demonstrated the anti-inammatory
potential of apple phenols on gastrointestinal cell inammation which involved downregulation of TNF and IL-6
cytokines35. Another means of action could involve the acetic acid component of ACV which is able to reduce
the cell hydrogen potential hence could potentially facilitate diusion across the plasma membrane of microbes.
Furthermore, there is evidence that organic acids can alter immune responses by binding to GPR3, a G pro-
tein coupled receptor which is mostly expressed on inammatory leukocytes36. Also, an investigation reported
on upregulated blood and plasma antioxidant enzyme release aer apple consumption which would encourage
immune protection16.
e positive benets of dietary ACV supplementation have been highlighted in vivo. ACV decreased the
serum lipid prole in mice fed a high cholesterol diet over 28 days. Intragastric ACV addition induced a pro-
tective eect against erythrocyte, kidney and liver oxidative injury as well as lowering cholesterol levels18. ACV
Protein name Mass
(Da)
Control
C.albicans
culture ACV- Treated
C.albicans cu lture
40S ribosomal protein S1 29083 * *
6-phosphogluconate dehydrogenase 71270 *
Alcohol dehydrogenase 1 37255 * *
Elongation factor 1-alpha 1 50436 * *
Elongation factor 2 93865 * *
Enolase 1 47202 * *
Fructose-bisphosphate aldolase 39362 *
Glucose-6-phosphate isomerase 61148 *
Glyceraldehyde-3-phosphate dehydrogenase 35925 * *
Heat shock protein SSA1 70452 * *
Mitochondrial outer membrane protein porin 29748 *
Peptidyl-prolyl cis-trans isomerase 17678 *
Phosphoglycerate kinase 45266 * *
Phosphoglycerate mutase 27437 * *
Plasma membrane ATPase 1 98083 * *
Pyruvate decarboxylase 62744 * *
Pyruvate kinase 55752 *
Small heat shock protein 21 21482 * *
Triosephosphate isomerase 26880 * *
White colony protein WHS11 6991 *
Table 4. List of C. albicans proteins identied following ACV treatment. C. albicans were cultured with 1/2
dilution of ACV or alone in broth for 24 hours at 37 °C in a shaking incubator. Aer which mass spectroscopy
analysis was carried out. e “*” indicates the presence of protein whilst the blank region denotes no detection
of that particular protein.
Content courtesy of Springer Nature, terms of use apply. Rights reserved
www.nature.com/scientificreports/
9
ScieNTific RepoRTS | (2018) 8:1732 | DOI:10.1038/s41598-017-18618-x
also decreased blood triglyceride and very low density lipoprotein levels in rats which had induced cholesterol
induced hepatic steatosis33. In an infection induced model of denture stomatitis, ACV addition resulted in
anti-fungal activity against Candida Spp which was comparable to nystatin in terms of reducing microbial adher-
ence and destruction37.
Severe infections, autoimmunity or transplantation can inevitably lead to ineective immunity in patients.
An analysis of macrophages from Crohn’s disease patients revealed that they had defective responses to E-coli
due to Crohn’s related systemic immunosuppression38. A recent report showed that co-administration of ACV
with L-casei boosted systemic and mucosal immune responses, antioxidant enzyme and growth genes in sh39.
Equally, perhaps additive dietary supplementation with ACV could be of benet in acute infections, autoimmune
induced immune dysregulation or antibiotic redundancy in humans. Future studies would establish whether
ACV could be used as a potential therapeutic, In vivo models of infection could be induced by infusing microbes
systemically into mice followed by treatment with or without intraperitoneal ACV. Intragastric ACV has been fed
to animals used as models of obesity and infection in the past18,37,39. ACV ecacy could be evaluated by meas-
uring microbial burden, serum cytokine levels, leukocyte counts and tissue pathology. Side eects could include
acid reux, nausea or delayed digestion as ACV has a pH of 4.2. However, the acidity could be neutralised by the
addition of sodium bicarbonate to preparations. e results of this study could have clinical implications as ACV
could be used as an additive component of an antimicrobial therapeutic regimen especially in immunocompro-
mised patients presenting with infections of the aforementioned microbes.
We conclude that ACV can have multiple antimicrobial eects directly on E-coli, S. aureus and C. albicans.
ACV addition can also decrease induced inammatory cytokine release during mononuclear leukocyte infection
and increases monocyte phagocytic capacity. Mechanisms include alteration of the microbial protein physiology
destroying structural pathogenic proteins and metabolic enzymes. Collectively our results highlight the potent
antimicrobial and therefore benecial actions of ACV. is preliminary study encourages further work on dietary
ACV supplementation investigating its antimicrobial role and the constituents which could be responsible for
this activity.
Materials and Methods
Chemical reagents, microorganisms, media and culture conditions. A selection of microbial spec-
imens which represented a typical gram positive, a gram negative and a yeast species were chosen for initial
investigation. Microbial strains: E-coli strain NCTC 10418 and S. aureus strains NCTC 6571 were purchased from
Health Protection Agency (Colindale, U.K.). C. albicans strain 90828 was purchased from the American Type
Culture Collection (LGC Promochem).
Reagents. Dulbecco’s modied media, dimethyl-ethyl-sulphonyl-oxide, HANKS balanced salt solution, his-
topaque, ethanol, phosphate buered saline, paraformaldehyde, acetone, dithiothreitol, iodoacetamide, trypsin
from porcine pancreas of proteomics grade, formic acid, acetonitrile, HPLC-grade water, methanol and Whatman
Mini-UniPrep syringeless lter devices (pore size 0.45 µm) were purchased from Sigma Aldrich (Poole, U.K.).
TNF-alpha, interleukin-6 (IL-6) enzyme linked immunosorbent assays (ELISA’s) were purchased from Research
and Development Systems (Abingdon, U.K.). Mueller hinton agar was purchased from Oxoid, UK. Braag’s
Apple Cider Vinegar and apple cider vinegar tablets (500 mg, Troo healthcare) were purchased from commercial
sources.
Inoculum preparation and measurement of anti-microbial activity of ACV. Cultures of E. coli and
S. aureus were grown in nutrient media whereas C. albicans was grown in Sabourand media. All cultures were
cultivated in a shaking incubator at 37 °C for 24 h overnight prior to use. Mueller hinton agar (MHA) was pre-
pared by dissolving 38 g in 1 litre of distilled water, boiling the mixture for 1 min, aer cooling and autoclaving,
the media was poured into petri dishes. e plates were le to dry and subsequently stored at 37 °C. All microbial
cultures were adjusted to 0.5 McFarland’s standard 1.5 × 108 CFU/ml and 4 × 106 CFU/ml of each organism used
in experiments. Each microbe was swabbed evenly onto plates containing MHA. For sample addition, 100 µL of
ACV at varying concentrations was added to the wells which were punched into the agar. e plates were then
incubated at 37 °C for 24 h. Zones of inhibition surrounding samples were identied, photographed and measured
in mm40. Experiments were repeated at least 5 times.
Ethical Approval and Informed Consent. All experimental protocols were approved by the Middlesex
University Natural Sciences Ethics Committee number 2323. Further the methods were carried out in accordance
to the relevant guidelines and regulations. Informed consent was received when applicable.
Human mononuclear cell isolation procedure from whole peripheral blood. Human leucocyte
rich cones and serum were obtained from volunteer donors collected from NHS Cord blood and transplant bank
at Colindale, London and treated as described previously41. Briey the cones were washed with phosphate buer
saline to harvest the leucocyte rich cells. ese were then spun on histopaque density gradient at 1200 RPM for
20 min. Monocytes were puried using the CD14 positive mononuclear portion which was isolated according to
manufacturer’s instruction provided with the pan monocyte isolation kit. Cells washed with HANKS balanced
solution, counted and cultured into 24 well plates at 4 × 105 cells per mL. Cells were allowed to adhere for an hour
at aer which non-adherent cells were washed away and full media replenished with Dulbecco’s media containing
10% human serum. Monocytes were determined using light microscopy and ow cytometry phenotypic analysis
of dierentiation markers as described previously using CD1441. Freshly isolated monocytes were cultured with
varying concentrations of ACV and either C. albicans, E. coli or S. aureus at counts of 4 × 106 CFU/ml respectively
Content courtesy of Springer Nature, terms of use apply. Rights reserved
www.nature.com/scientificreports/
10
ScieNTific RepoRTS | (2018) 8:1732 | DOI:10.1038/s41598-017-18618-x
for 24 h at 37 °C and 5% CO2 aer which supernatants were collected and analysed for TNF-α or IL-6 secretion
using ELISA kits following manufacturer’s protocols.
Monocyte phagocytic capacity measurement by ow cytometry. Isolated human mononuclear
cells were cultured at 4 × 105/mL in 24 well plates over a period of two days aer which they were incubated with
microbes (4 × 106 CFU/ml) for 4 h at 37 °C and 5 CO2. Cells were then scraped replenished in ice cold PBS con-
taining 1 mM EDTA, washed and removed from plates. e resultant pellets were xed in 400 µL of 4% paraform-
aldehyde and analysed using a FACS Calibur ow cytometer (Beckton Dickinson Immunocytometry Systems,
UK and Cell Quest soware).
Preparation of microbial tryptic digests for mass spectroscopy analysis. An aliquot of microbial
suspension was collected and treated over 24 h with 1/100 ACV, washed with PBS, resuspended in PBS and then
treated with 1 mL of ice-cold acetone. e bacterial cells were harvested aer centrifugation 13,000 g for 5 min.
e pellet was dried and then reconstituted in 50 mM ammonium bicarbonate. Cells were lysed using a Soniprep
150 Plus (MSE, U.K.) for 10 s with the amplitude set at 13. Subsequently proteins were denatured and reduced
with 3 μL of 100 mM dithiothreitol in 50 mM ammonium bicarbonate at 95 °C for 5 min followed by alkylation
with 6 μL of 100 mM iodoacetamide in the dark at room temperature for 20 min. Proteins were then digested with
2 μL of trypsin (0.1 μg/μL dissolved in 50 mM ammonium bicarbonate) at 37 °C for 3 h. A further 2 μL of trypsin
was added to the sample and the mixture was incubated at 37 °C for an additional 2 h. e samples were diluted in
150 µL 50 mM ammonium bicarbonate and passed through Mini-Uni Prep lter devices.
Liquid Chromatography-Electrospray Ionisation Tandem Mass Spectrometry. e tryptic pep-
tides were analysed using a Shimadzu Prominence HPLC system hyphenated to an electrospray ionisation hybrid
ion-trap time-of-ight (IT-TOF) mass spectrometer (Shimadzu, U.K.) operated in tandem mass spectrometry
mode. Peptides were separated using an Ascentis Express 150 × 2.1 mm, 2.7 µm C18 column (Sigma-Aldrich,
Poole, U.K.) using a ow rate of 0.21 mL/min. e column oven temperature was set to 40 °C. Data was acquired
and processed using LabSolutions®soware (version 3.50.348, Shimadzu, UK). A linear gradient elution prole
composed of ‘A’−0.1% formic acid in water and ‘B’- 0.1% formic acid in acetonitrile was used. e gradient
prole was 0–40% B, 70 min; 40–90% B, 1 min; maintained at 90% B, for 3 min; 90–0% B, 1 min; and 15 min
re-equilibration at 0% B. An injection volume of 40 µL was used. Samples were kept in the auto sampler set to
4 °C. Mass spectrometry analysis was performed in MS/MS mode using positive ions electrospray. e precursors’
acquisition range was set to 400–1,800 m/z while the fragments acquisition range was set to 200–1,500 m/z. For
both precursors and fragments the ion accumulation time was set to 30 msec. e other instrument conditions
were set as follows: detector voltage 1.6 kV, CID energy 70%, nebulising gas ow 1.5 L/min, CDL temperature
200 °C, heat block temperature 200 °C, interface voltage 4.5 V, detector voltage 2 kV. e data acquisition was
performed in a 37.5 min interval.
LC-MS/MS Data Processing. MS/MS data were extracted from the resulting instrument les using Mascot
Distiller soware (version 2.5.1.0, Matrix Science, London, UK). For precursors peak picking the following
parameters were used: correlation threshold – 0.7, minimum signal to noise ratio – 5, minimum peak m/z – 50,
maximum peak m/z – 100,000, minimum peak width – 0.02 Da, expected peak width – 0.2 Da, maximum peak
width – 2 Da. e MS/MS ion list was searched using Mascot search engine against all entries in Swiss-Prot data-
base (2016_2). For database search the following parameters were used: two missed cleavages, carbamidometh-
ylation of cysteine (as xed modication) and oxidation of methionine (as variable modication). e tolerance
for precursor peptides was set to 10 ppm and for fragments to 0.3 Da. Peptide charges used for peak picking was
+2, +3 and +4.
Statistical analysis. All experimental results are expressed as the mean ± standard deviation (SD). Statistical
analyses was carried out using one way ANOVA or students t-test, outcomes were considered signicant where
p < 0.05 (when comparing apple cider vinegar treated microbes to the untreated groups in all experiments). All
experiments were repeated at least 3–5 times. Analysis was carried out using Excel soware version 2016.
Data availability. e datasets generated and analyzed during the current study reside with the correspond-
ing author and can be made available upon request.
References
1. World Health Organization (WHO). Global priority list of antibiotic-resistant bacteria to guide research, discovery, and
development of new antibiotics. Geneva: Switzerland (2017).
2. Mora-illo, M. et al. Impact of virulence genes on sepsis severity and survival in Escherichia coli bacteraemia. Virulence. 6, 93–100
(2015).
3. ittirsch, D., Flierl, P. A. & Ward, M. A. Harmful molecular mechanisms in sepsis. Nature eviews Immunology. 8, 776–787 (2008).
4. Cigana, C., Assaei, B. M. & Melotti, P. Azithromycin selectively reduces tumour necrosis factor alpha levels in cystic brosis airway
epithelial cells. Antimicrob agents Chemother. 51, 975–81 (2007).
5. Culic, O. et al. Azithromycin modulates neutrophil function and circulating inammatory mediators in healthy human subjects. Eur
J Pharmacol. 450, 277–89 (2002).
6. Marbach, H. et al. Identication of a distinctive phenotype for endocarditis-associated clonal complex 22 MSA isolates with
reduced vancomycin susceptibility. J Med Microbiol. 66, 584–591 (2017).
7. Aghai, Z. H. et al. Azithromycin suppresses activation of nuclear factor appa B and synthesis of pro-inammatory cytoines in
tracheal aspirate cells from premature infants. Pediatr es. 62, 483–8 (2007).
8. Nurjadi, D., lein, S., Zimmermann, S., Heeg, . & Zanger, P. Transmission of ST8-USA300 Latin American Variant Methicillin-
esistant Staphylococcus aureus on a Neonatal Intensive Care Unit: ecurrent Sin and So- Tissue Infections as a Marer for
Content courtesy of Springer Nature, terms of use apply. Rights reserved
www.nature.com/scientificreports/
11
ScieNTific RepoRTS | (2018) 8:1732 | DOI:10.1038/s41598-017-18618-x
Epidemic Community-Associated-MSA Colonization. Infect Control Hosp Epidemiol. 18, 1–3, https://doi.org/10.1017/ice.2017.88
(2017).
9. Ward, D. V. et al. Metagenomic Sequencing with Strain-Level esolution Implicates Uropathogenic E. coli in Necrotizing
Enterocolitis and Mortality in Preterm Infants. Cell ep. 14, 2912–24 (2016).
10. Flores-Mireles, A. L., Waler, J. N., Caparon, M. & Hultgren, S. J. Urinary tract infections: epidemiology, mechanisms of infection
and treatment options. Nat ev Microbiol. 13, 269–84 (2015).
11. Çe, M. et al. Antibiotic prophylaxis in urology departments. global prevalence study of infections in urology investigators. Eur Urol.
63, 386–94 (2013).
12. Sullivan, S. B. et al. educed vancomycin susceptibility of methicillin-susceptible Staphylococcus aureus: no signicant impact on
mortality but increase in complicated infection. Antimicrob Agents Chemother. AAC.00316–17, https://doi.org/10.1128/AAC.00316-
17 (2017).
13. Hippocrates: e Genuine Wors of Hippocrates. Volume I and II. Edited by: Adams F. New Yor: William Wood and Company
(1886).
14. Ebner, H., Farnworth, H. & Sellemer, S. Vinegar in biotechnology: A multi-volume comprehensive treatise, 2nd edition, 579–91
(1995).
15. del Campo, G., Berregi, I., Santos, J. I., Dueñas, M. & Irastorza, A. Development of alcoholic and malolactic fermentations in highly
acidic and phenolic apple musts. Bioresour Technol. 99, 2857–63 (2008).
16. Avci, A. et al. Eects of apple consumption on plasma and erythrocyte antioxidant parameters in elderly subjects. Exp Aging es. 33,
429–37 (2007).
17. Pourmouzaar, S., Hajimardloo, A. & Mindare, H. . Dietary eect of apple cider vinegar and propionic acid on immune related
transcriptional response and growth performance in white shrimp. Litopenaeus vannamei. Fish Shellsh Immunology. 60, 60–71
(2017).
18. Nazıroğlu, M. et al. Apple cider vinegar modulates serum lipid prole, erythrocyte, idney, and liver membrane oxidative stress in
ovariectomized mice fed high cholesterol. J Membr Biol. 24, 667–73 (2014).
19. Palasa, I., Gagari, E. & eoharides, T. C. e eects of P. gingivalis and E.coli LPS on the expression of proinammatory mediators
in human mast cells and their relevance to periodontal disease. J. Biol egul Homeost agents. 30, 655–664 (2016).
20. Swan, Z. D., Bouwer, A. L., Wonderlich, E. . & Barrat-Boyes, S. M. Persistent accumulation of gut macrophages with impaired
phagocytic function correlates with SIV disease progression in macaques. Eur J Immunol. https://doi.org/10.1002/eji.201646904
(2017).
21. Walborn, A., Hoppensteadt, D., Syed, D., Mosier, M. & Fareed, J. Biomarer Prole of Sepsis-Associated Coagulopathy Using
Biochip Assay for Inammatory Cytoines. Clin Appl romb Hemost., https://doi.org/10.1177/1076029617709084 (2017).
22. Procenca, J. T., Barral, D. C. & Gordo, I. Commensal to pathogen: One single transposon insertion results in two pathoadaptive traits
to Escherichia coli-macrophage interaction. Sci eports 7(1), 4504, https://doi.org/10.1038/s41598-017-04081-1 (2017).
23. Jahan, N., Maeda, ., Matsuoa, Y., Sugimoto, Y. & urata, H. Development of an accurate inetic model for the central carbon
metabolism of Escherichia coli. Microb Cell Fac t. 21–15(1), 112, https://doi.org/10.1186/s12934-016-0511-x (2016).
24. Calhoun, L. N. & won, Y. M. Structure, function and regulation of the DNA-binding protein Dps and its role in acid and oxidative
stress resistance in Escherichia coli: a review. J Appl Microbiol. 110(2), 375–86, https://doi.org/10.1111/j.1365-2672.2010.04890.x
(2011).
25. awashima, S. A. et al. Potent reversible and potent chemical inhibitors of euaryotic ribosome biogenesis. Cell. 30, 1573–88 (2016).
26. Singh, V. . et al. ole for dna locus in tolerance of multiple stresses in Staphylococcus aureus. Microbiology. 153, 3162–3173
(2007).
27. Ginguay, A., Cynober, L., Curis, E. & Nicolis, I. Ornithine Aminotransferase, an Important Glutamate-Metabolizing Enzyme at the
Crossroads of Multiple Metabolic Pathways. Biology. 7, 6(1). pii: E18. https://doi.org/10.3390/biology6010018 (2017).
28. Martins, . N., Harper, C. G., Stoes, G. B. & Masters, C. L. Increased cerebral glucose-6-phosphate dehydrogenase activity in
Alzheimer’s disease may reect oxidative stress. J Neurochem. 46, 1042–1045 (1986).
29. elly, J. & avanagh, . Proteomic analysis of protein released from growth arrested candida albicans following exposure to
caspofungin. Med Mycol. 48, 598–605 (2010).
30. Ni, W. et al. Escherichia coli maltose-binding protein activates mouse peritoneal macrophages and induces M1 polarization via
TL2/4 in vivo and in v itro. Int Immunopharmacol. 21, 171–80 (2014).
31. Bengtsson, A. et al. Anti-TNF treatment of baboons with sepsis reduces TNF-alpha, IL-6 and IL-8, but not the degree of complement
activation. Scand J Immunol. 48, 509–14 (1998).
32. Simisopoulou, M. et al. Dierential expression of cytoines and chemoines in human monocytes induced by lipid formulations of
amphotericin B. Antimicrob Agents Chemother. 49, 1397–1403 (2005).
33. Buda, N. H. et al. Eects of apple cider vinegars produced with dierent techniques on blood lipids in high-cholesterol-fed rats. J
Agric Food Chem. 22–59(12), 6638–44, https://doi.org/10.1021/jf104912h (2011).
34. Yang, J., Li, Y., Wang, F. & Wu, C. Hepatoprotective eects of apple polyphenols on CCI4-induced acute liver damage in mice. J Agri c
Food Chem. 26–58(10), 6525–31 (2010).
35. Denis, M. C. et al. Apple peel polyphenols and their benecial actions on oxidative stress and inammation. Furtos A, Dudonne S,
Montoudis A, Garofalo C, Desjardins Y, D elvin E, Levy E. PLoS One 8(1) (2013).
36. Maslowsi, . M. & Macay, C. . Diet, gut microbiota and immune responses. Nat Immunol. 12(1), 5–9, https://doi.org/10.1038/
ni0111-5 (2011).
37. Mota, A. C. et al. Antifungal Activity of Apple Cider Vinegar on Candida Species Involved in Denture Stomatitis. J Prosthodont.
24(4), 296–302, https://doi.org/10.1111/jopr.12207 (2015).
38. Vazeille, E. et al. Monocyte-derived macrophages from Crohn’s disease patients are impaired in the ability to control intracellular
adherent-invasive Escherichia coli and exhibit disordered cytoine secretion prole. J Crohns Colitis. 9(5), 410–20, https://doi.
org/10.1093/ecco-jcc/jjv053. (2015).
39. Safari, ., Hoseinifar, S. H., Nejadmoghadam, S. & halili, M. Apple cider vinegar boosted immunomodulatory and health
promoting eects of Lactobacillus casei in common carp (Cyprinus carpio). Fish Shellsh Immunol. 7(67), 441–448, https://doi.
org/10.1016/j.fsi.2017.06.017 (2017).
40. Ostrovsy, E. A. et al. Methods for the antimicrobial activity and determination of minimum inhibitory concentration of planrt
extracts. Brazilian J Pharmacogn. 18, 301–7 (2008).
41. Yagni, D. Macrophage derived platelet activating factor implicated in the resolution phase of gouty inammation. Int J Inam.
526496, https://doi.org/10.1155/2014/526496 (2014).
Acknowledgements
We would like to thank Manika Choudhury and Alejandra Gonzalez Baez for their technical assistance.
Author Contributions
D.Y. conceived and performed the experiments, data analysis and wrote the manuscript. V.S. contributed to the
mass spectroscopy experiments and data analysis. A.S. contributed to manuscript writing and data review.
Content courtesy of Springer Nature, terms of use apply. Rights reserved
www.nature.com/scientificreports/
12
ScieNTific RepoRTS | (2018) 8:1732 | DOI:10.1038/s41598-017-18618-x
Additional Information
Competing Interests: e authors declare that they have no competing interests.
Publisher's note: Springer Nature remains neutral with regard to jurisdictional claims in published maps and
institutional aliations.
Open Access This article is licensed under a Creative Commons Attribution 4.0 International
License, which permits use, sharing, adaptation, distribution and reproduction in any medium or
format, as long as you give appropriate credit to the original author(s) and the source, provide a link to the Cre-
ative Commons license, and indicate if changes were made. e images or other third party material in this
article are included in the article’s Creative Commons license, unless indicated otherwise in a credit line to the
material. If material is not included in the article’s Creative Commons license and your intended use is not per-
mitted by statutory regulation or exceeds the permitted use, you will need to obtain permission directly from the
copyright holder. To view a copy of this license, visit http://creativecommons.org/licenses/by/4.0/.
© e Author(s) 2018
Content courtesy of Springer Nature, terms of use apply. Rights reserved
1.
2.
3.
4.
5.
6.
Terms and Conditions
Springer Nature journal content, brought to you courtesy of Springer Nature Customer Service Center GmbH (“Springer Nature”).
Springer Nature supports a reasonable amount of sharing of research papers by authors, subscribers and authorised users (“Users”), for small-
scale personal, non-commercial use provided that all copyright, trade and service marks and other proprietary notices are maintained. By
accessing, sharing, receiving or otherwise using the Springer Nature journal content you agree to these terms of use (“Terms”). For these
purposes, Springer Nature considers academic use (by researchers and students) to be non-commercial.
These Terms are supplementary and will apply in addition to any applicable website terms and conditions, a relevant site licence or a personal
subscription. These Terms will prevail over any conflict or ambiguity with regards to the relevant terms, a site licence or a personal subscription
(to the extent of the conflict or ambiguity only). For Creative Commons-licensed articles, the terms of the Creative Commons license used will
apply.
We collect and use personal data to provide access to the Springer Nature journal content. We may also use these personal data internally within
ResearchGate and Springer Nature and as agreed share it, in an anonymised way, for purposes of tracking, analysis and reporting. We will not
otherwise disclose your personal data outside the ResearchGate or the Springer Nature group of companies unless we have your permission as
detailed in the Privacy Policy.
While Users may use the Springer Nature journal content for small scale, personal non-commercial use, it is important to note that Users may
not:
use such content for the purpose of providing other users with access on a regular or large scale basis or as a means to circumvent access
control;
use such content where to do so would be considered a criminal or statutory offence in any jurisdiction, or gives rise to civil liability, or is
otherwise unlawful;
falsely or misleadingly imply or suggest endorsement, approval , sponsorship, or association unless explicitly agreed to by Springer Nature in
writing;
use bots or other automated methods to access the content or redirect messages
override any security feature or exclusionary protocol; or
share the content in order to create substitute for Springer Nature products or services or a systematic database of Springer Nature journal
content.
In line with the restriction against commercial use, Springer Nature does not permit the creation of a product or service that creates revenue,
royalties, rent or income from our content or its inclusion as part of a paid for service or for other commercial gain. Springer Nature journal
content cannot be used for inter-library loans and librarians may not upload Springer Nature journal content on a large scale into their, or any
other, institutional repository.
These terms of use are reviewed regularly and may be amended at any time. Springer Nature is not obligated to publish any information or
content on this website and may remove it or features or functionality at our sole discretion, at any time with or without notice. Springer Nature
may revoke this licence to you at any time and remove access to any copies of the Springer Nature journal content which have been saved.
To the fullest extent permitted by law, Springer Nature makes no warranties, representations or guarantees to Users, either express or implied
with respect to the Springer nature journal content and all parties disclaim and waive any implied warranties or warranties imposed by law,
including merchantability or fitness for any particular purpose.
Please note that these rights do not automatically extend to content, data or other material published by Springer Nature that may be licensed
from third parties.
If you would like to use or distribute our Springer Nature journal content to a wider audience or on a regular basis or in any other manner not
expressly permitted by these Terms, please contact Springer Nature at
onlineservice@springernature.com
Available via license: CC BY 4.0
Content may be subject to copyright.
