Spelling suggestions: "subject:"tyrocidine"" "subject:"tyrosines""
1 |
NMR studies of the solution conformation and dynamics of the tyrocidine peptide antibioticsChou, Ning. January 1985 (has links)
Thesis (Ph. D.)--University of Wisconsin--Madison, 1985. / Typescript. Vita. Includes bibliographies.
|
2 |
Optimization of antibacterial cyclic decapeptides : tyrocidine A /Ng, Na Lee. January 2004 (has links)
Thesis (M.Phil.)--Hong Kong University of Science and Technology, 2004. / Includes bibliographical references (leaves 148-151). Also available in electronic version. Access restricted to campus users.
|
3 |
Characterisation of small cyclic peptides with antilisterial and antimalarial activityLeussa, Nyango-Nkeh Adrienne 04 1900 (has links)
Thesis (PhD)--Stellenbosch University, 2014. / ENGLISH ABSTRACT: Antimicrobial peptides (AMPs) are currently the most researched group of compounds for new
antimicrobial drugs especially with the rise in resistance to almost all available drugs by public
health relevant pathogens. In this study we set out to characterise small cyclic AMPs in terms of
their activity towards human pathogens Listeria monocytogenes, a food-borne pathogen causing
listeriosis and Plasmodium falciparum, a parasite that causes malaria respectively, each a threat
to public health.
One of the small cyclic peptide libraries examined is the tyrocidines (Trcs) and analogues, which
are cyclic decapeptides [cyclo-(D-Phe-Pro-(Phe/Trp)-D-Phe/DTrp)-Asn-Gln-(Tyr/Phe/Trp)-Val-
(Orn/Lys)-Leu] produced by the Gram-positive bacteria Bacillus aneurinolyticus as part of the
tyrothricin complex which is non-ribosomally synthesised during sporulation. Previous research
found that the six major Trcs were active against Listeria monocytogenes and Plasmodium
falciparum and it was found that the identity of the aromatic residues in the aromatic dipeptide
unit has an important role in activity. We set out to extend the qualitative structure to activity
relationship (QSAR) studies using more Trc analogues and small synthetic Arg- and Trp-rich
cyclic peptides (RW-peptides) in a bid to establish essential structural motifs and pre-requisites
for activity. Eight natural and three synthetic Trc analogues and fifteen RW-peptides were either
naturally or by chemical synthesis produced and characterised in terms of chemical character and
biological activity. The Trcs were significantly more active than RW peptides, although much
more haemolytic and thus toxic. Results indicated the relevance for hydrogen bonding with an
aromatic amino acid residue for selective activity towards the leucocin A resistant L.
monocytogenes B73-MR1. However, structural properties favouring a tighter membrane
interaction hindered the Trc mode of action (MOA). We determined that Gln6 and hydroxyl
group of Tyr7 may be involved in interaction with the putative target in L. monocytogenes. There
was also need for an amphipathic balance between hydrophobicity and size/steric parameters for
optimal activity. From our QSAR studies we predict as lead peptide for a future library of
antilisterial Trcs: cyclo(VOMe3LfPWfNQY). Furthermore, the antilisterial activity of the Trcs
was found to be predominantly lytic and salt tolerant while RW-peptides were non-lytic and
sensitive to Ca2+. We confirmed that Ca2+ enhanced Trc antilisterial activity with Ca2+ increasing
the Trc anti-metabolic activity, but conversely inducing a non-lytic mechanism of action. From model membrane studies, we propose that the calcium induced Trc non-lytic MOA could be due
to detrimental lipid demixing, presence of a Trc sensitive Ca2+-induced non-membrane target in
the prematurely calcium induced intracellular anaerobic form of Listeria monocytogenes, and/or
the Trc-Ca2+ complexes may inhibit key components such as membrane bound electron transport
system or bacterial dehydrogenases.
We confirmed, as previously found, that the Trcs have potent antimalarial activity that is
sequence specific and non-lytic. The RW-peptides had very weak activity, but our results again
indicated that more hydrophobic and haemolytic peptides tend to be more active, particularly the
RW-peptide containing the Trp analogue β-(benzothien-3-yl)-alanine (Bal). A novel finding was
that one of the more polar Trc C analogues, namely tryptocidine C (Tpc C), in contrast to Trc C
showed potent antimalarial activity indicating the specific sequence and the role of the Trp7 in
activity. From these results a proposed lead peptide for future research is
cyclo[VOLfP(Bal)fNQ(Bal)]. Furthermore, in our search for the Trc and Tpc C target(s) we
employed high resolution fluorescence microscopy. Results show that Trc led to disorganisation
of neutral lipid structures and chromatin halting growth in late trophozoite/early schizont stages.
This indicated that membrane structures containing neutral lipids, as well as chromatin may be
targeted by the Trcs. Another novel finding in our studies was that chloroquine (CQ) resistance
not only correlated with resistance to Trcs, but the Trcs and CQ were found to be antagonistic
towards each other’s activity. This indicated a shared target and we propose the food vacuole as
another of the Trc targets in P. falciparum. / AFRIKAANSE OPSOMMING: Antimikrobiese peptiede (AMPe) is tans die mees nagevorsde groep verbindings in die soeke na
nuwe antimikrobiese middels, veral weens 'n toenemende weerstandigheid van patogene in die
openbare gesondheidsektor teen alle beskikbare middels. Die doel van hierdie studie was om
klein, sikliese AMPe in terme van hul aktiwiteit teenoor twee menslike patogene wat 'n
bedreiging vir openbare gesondheid is, Listeria monocytogenes, 'n voedsel-oordraagbare
patogeen wat listeriose veroorsaak, asook Plasmodium falciparum, die parasiet verantwoordelik
vir malaria, te karakteriseer.
Een van die klein, sikliese peptiedbiblioteke wat ondersoek is, is die tyrocidines (Trcs) en analoë
(sikliese dekapeptiede [siklo-(D-Phe-Pro-(Phe/Trp)-D-Phe/DTrp)-Asn-Gln-(Tyr/Phe/Trp)-Val-
(Orn/Lys)-Leu]). Hierdie peptiede deur die Gram-positiewe bakterie Bacillus aneurinolyticus
word wat nie-ribosomaal gesintetiseer as deel van die tirotrisien kompleks word tydens
sporulasie. Vorige navorsing het gewys dat die ses hoof Trcs teen Listeria monocytogenes en
Plasmodium falciparum aktief is en dat die identiteit van die aromatiese residue in die aromatiese
dipeptiedeenheid 'n belangrike rol speel in die Trc-aktiwiteit. Ons het gepoog om die
kwalitatiewe struktuur-aktiwiteit-verwantskap (QSAR) studies uit te brei deur meer Trc analoë
en klein sintetiese Arg- en Trp-ryke sikliese peptiede (RW-peptiede) te gebruik en sodoende
essensiële struktuur-motiewe en voorvereistes vir aktiwiteit vas te stel. Agt natuurlike en drie
sintetiese Trc analoë, asook vyftien RW-peptiede is of deur natuurlike of chemiese sintese
geproduseer en gekarakteriseer in terme van chemiese karakter en biologiese aktiwiteit. Die Trcs
het beduidend meer aktiwiteit as RW-peptiede getoon, maar is ook meer hemolities en dus meer
toksies. Die resultate dui op die belang van waterstofbinding met 'n aromatiese aminosuurresidu
vir die selektiewe aktiwiteit teenoor die leucocin A weerstandige L. monocytogenes B73-MR1.
Strukturele eienskappe wat tot 'n sterker membraan-interaksie lei, verhinder egter die
werkingsmeganisme. Ons het vasgestel dat Gln en die hidroksielgroep van Tyr betrokke kan
wees in die interaksie met die vermeende teenmiddelteiken in L. monocytogenes. 'n Balans tussen
amfipatiese/hidrofobiese en grootte/steriese parameters is ook noodsaaklik vir optimale
aktiwiteit. Vanuit ons QSAR studies word die peptied siklo-(VOMe3LfPWfNQY) as die
voorloper vir 'n toekomstige peptiedbiblioteek van antilisteriale Trcs voorgestel. Verder is daar
gevind dat die antilisteriese aktiwiteit van die Trcs oorwegend lities en sout-verdraagsaam is, terwyl die RW-peptiede nie-lities en Ca2+ sensitief is. Ons het bevestig dat Ca2+ die Trc
antilisteriese aktiwiteit verbeter, deur die Trc se antimetaboliese aktiwiteit verhoog, maar
terselfdertyd 'n nie-litiese werkingsmeganisme induseer. Vanuit model-membraan studies word
voorgestel dat Trc se nie-litiese werkingsmeganisme, soos teweeggebring deur Ca2+, die gevolg
kan wees van nadelige lipied vermenging, die teenwoordigheid van 'n kalsium geïnduseerde Trcsensitiewe
nie-membraan teiken in 'n vervroegde kalsium geïnduseerde intrasellulêre anaerobiese
vorm van Listeria monocytogenes, en/of dat die Trc-Ca2+ komplekse belangrike komponente
soos ’n membraan-gebonde elektron transport sisteem of bakteriële dehidrogenases inhibeer.
Daar is ook bevestig, soos voorheen gevind, dat die Trcs kragtige, antimalaria aktiwiteit besit wat
volgorde-spesifiek en nie-lities is. Die RW-peptiede het swak aktiwiteit getoon, maar ons
resultate het weereens bewys dat peptiede wat meer hidrofobies en hemolities is, meer aktief is,
veral die RW-peptiede wat die Trp analoog β-(bensoteïen-3-iel)-alanien (Bal) bevat. 'n Nuwe
bevinding is dat een van die meer polêre Trc C analoë, genaamd triptosidien C (Tpc C), in
teenstelling met Trc C, sterk antimalaria aktiwiteit het, wat 'n aanduiding is van die spesifieke
volgorde en die rol van die Trp7 in aktiwiteit. Vanuit hierdie bevindinge word die peptied siklo-
(VOLfP(Bal)fNQ(Bal)) as 'n voorloper vir toekomstige navorsing aangedui.
Vir ons soeke na die Trc en Tpc C teiken(s), het ons hoë resolusie fluoressensie mikroskopie
aangewend. Resultate toon dat Trc tot die ontwrigting van 'n neutrale lipied strukture en
chromatien lei en sodoende groei beperk in die laat trofosoïet/vroeë skisont fases. Dit het
aangedui dat die membraanstrukture wat neutrale lipiede bevat, sowel as chromatien, deur die
Trcs geteiken word. 'n Verdere nuwe bevinding in hierdie studie was dat chloroquine (CQ)
weerstandigheid nie net korreleer met weerstandigheid teen Trcs nie, maar dat die Trcs en CQ
antagonisties optree teenoor mekaar se aktiwiteite. Dit dui op 'n gemeenskaplike teiken en die
kosvakuool as 'n addisionele Trc teiken in P. falciparum word voorgestel.
|
4 |
Qualitative structure-activity relationships of the major tyrocidines, cyclic decapeptides from Bacillus aneurinolyticusSpathelf, Barbara Marianne 03 1900 (has links)
Thesis (PhD (Biochemistry))--University of Stellenbosch, 2010. / ENGLISH ABSTRACT:
The need for alternative or supplementary treatments due to the global problem of
microbial resistance towards conventional antimicrobials may be met by the
development of novel drugs based on antimicrobial peptides. The antimicrobial peptides
of interest to this study were the tyrocidines, cyclic decapeptides produced by Bacillus
aneurinolyticus. Although these antimicrobial peptides were the first natural antibiotic
to be discovered though a systematic search for antibacterial compounds, information
regarding their bioactivity, structure-activity relationships, determinants of bioactivity
and mode of action is limited. The aim of this study was to investigate the antibacterial
and antiplasmodial activity, as well as to identify determinants of bioactivity
modulation, of the natural tyrocidine library.
The study indicated that the tyrocidines exhibit significant activity toward
Gram-positive bacteria, notably Listeria monocytogenes, and the intraerythocytic
parasite, Plasmodium falciparum. Both the antilisterial and antiplasmodial activity was
found to be highly dependent on peptide identity and self-assembly. The antilisterial
activity of the tyrocidines was shown to be associated with increased self-assembly
within a membrane-like environment, which suggested that formation of lytic
complexes within the bacterial membrane may play a crucial role in tyrocidine activity.
In contrast to the observations for antilisterial activity, the antiplasmodial activity of the
tyrocidines was shown to be associated with reduced self-assembly within a
membrane-like environment, which suggested that the antiplasmodial activity of the
tyrocidines is mediated by a mechanism other than the formation of lytic complexes
within the target cell membrane.
In addition to the influence of peptide identity and self-assembly, the bioactivity of the
tyrocidines was found to be highly sensitive to environmental conditions, notably the
presence of calcium. The antilisterial activity, as well as the mode of action, of the
tyrocidines was also found to be highly sensitive to tyrocidine-Ca2+ complexation and
the concomitant induction of higher-order structures. Tyrocidine-Ca2+ complexation
was shown to greatly enhance antilisterial activity and change the mechanism of action
from a predominantly membranolytic to an alternative, non-lytic mode of action. The results of this investigation suggest that the alternative mode of tyrocidine activity
may be related to complexation with Ca2+. It is hypothesised that such complexation
may either (1) promote tyrocidine-DNA complexation, and thus inhibition of
transcription and/or replication; or (2) interfere with Ca2+ homeostasis, and thus
influence vital cell functions.
Overall, it may be hypothesised that tyrocidine activity and mode of action is modulated
by a critical play-off between self-assembly, cation-complexation and
membrane-interaction. As these modulators of activity are highly dependent on
tyrocidine sequence/structure, the wide variety of tyrocidines found in the natural
complex may allow for optimal interaction with and activity toward a variety of
microbes. / AFRIKAANSE OPSOMMING:
Die universele probleem van mikrobiese weerstand teen konvensionele antimikrobiese
middels en die wêreld-wye noodsaaklikheid vir alternatiewe of bykomende behandeling
mag deur die ontwikkeling van nuwe middels, gebasseer op antimikrobiese peptiede,
vervul word. Die antimikrobiese peptiede van belang tot hierdie studie is die tirosidiene,
sikliese dekapeptiede wat deur Bacillus aneurinolyticus geproduseer word. Informasie
ten opsigte van die tirosidiene se bioaktiwiteit, struktuur-funksieverwantskap,
determinante van bio-aktiwiteit en meganisme van aksie was beperk, alhoewel hierdie
peptiede die eerste antimikrobiese peptiede was wat ontdek is deur ‘n sistematiese
soektog vir antimikrobiese middels. Die doelwit van hierdie studie was die ondersoek
van antibakteriële and antiplasmodiese aktiwiteit, sowel as om die determinante van
bio-aktiwiteit modulering van die natuurlike tirosidienbiblioteek te ondersoek.
Hierdie studie het getoon dat die tirosidiene merkwaardige aktiwiteit teenoor
Gram-positiewe bakterië, in besonder Listeria monocytogenes het, asook teenoor die
intra-eritrositiese parasiet, Plasmodium falciparum. Daar is bevind dat beide die antilisteriese
en antiplasmodiese aktiwiteite hoogs afhanklik is van peptiedidentiteit en
self-verpakking. Daar is gewys dat die antilisteriese aktiwiteit van die tirosidiene
geassosieer is met verhoogde self-verpakking in ’n membraanagtige omgewing, wat ’n
aanduiding is dat die vorming van litiese komplekse in die bakteriële membraan ’n
kritiese rol in tirosidienaktiwiteit speel. Kontrasterend tot die waarnemings van
antilisteriese aktiwiteit, is getoon dat die antiplasmodiese aktiwiteit van die tirosidiene
geassosieer is met verlaagde self-verpakking in ’n membraanagtige omgewing. Dis ’n
aanduiding dat die antiplasmodiese aktiwiteit van die tirosidiene gemediëer word deur
‘n ander meganisme en nie die vorming van litiese komplekse in die teikenselmembraan
nie.
Bykomend tot die invloed van peptiedidentiteit en self-verpakking, is daar bevind dat
die bioaktiwiteit van die tirosidiene hoogs sensitief is vir die omgewing, in besonder die
teenwoordigheid van kalsium. Daar is ook bevind dat die antilisteriese aktiwiteit, sowel
as die meganisme van aksie, van tirosidiene hoogs sensitief is vir tirosidien-Ca2+
kompleksvorming en die gevolglike induksie van of hoër-orde strukture. Daar is gewys dat tirosidien-Ca2+ kompleksvorming die antilisteriese aktiwiteit drasties verhoog en dat
die meganisme van aksie verander van ’n oorwegende membranolitiese meganisme na
’n alternatiewe nie-litiese meganisme van aksie.
Die resultate van hierdie ondersoek het aangedui dat die alternatiewe meganisme van
aksie van tirosidienaktiwiteit moontlik verband kan hou met kompleksvorming met
Ca2+. Die hipotese is dat sodanige kompleksvorming moontlik of (1) tirosidien-DNA
komplekvorming aanmoedig, en dus transkripsie en/of replikasie inhibibeer of (2) met
Ca2+ homeostase inmeng, en sodoende lewensnoodsaaklike selfunksies beïnvloed.
Die algemene hipotese is dat tirosidienaktiwiteit en meganisme van aksie deur ’n
kritiese spel tussen self-verpakking, katioonkompleksvorming en membraaninteraksie
gemoduleer word. Die wye verskeidenheid van tirosidiene, wat in die natuurlike
kompleks gevind word, kan moontlik toelaat vir die optimale interaksie met, en
aktiwiteit teenoor ’n verskeidenheid van mikrobes, aangesien die aktiwiteitmoduleerders hoogs afhanklik is van tirosidien struktuur/volgorde.
|
5 |
Characterization of natural antimicrobial peptides adsorbed to different matricesvan Rensburg, Wilma 12 1900 (has links)
Thesis (MSc)--Stellenbosch University, 2015. / ENGLISH ABSTRACT: Biofouling is the attachment and biofilm formation that leads to negative repercussions such as
persistent post-harvest infections, infections obtained from medical implants and continual
surface contamination of food processing plants. Much of the problem lies with the resistance
that develops against conventional treatments due to the formation of mature biofilms. Thus the
focus has shifted from the removal of biofilms to the prevention of initial attachment of
organisms. This entails the use of antimicrobial surfaces that either have an inherent
antimicrobial activity, e.g. certain metals, or surfaces that are modified by the attachment of
antimicrobial agents. The attachment of antimicrobial agents can either be through covalent
bonding or adsorption, depending on the intended use of the surface as well as the mode of action
of the antimicrobial agent. Antimicrobial peptides (AMPs) are ubiquitous in nature, tend to have
a broad spectrum of activity, are very stable and have been shown to maintain activity when
covalently bound to solid surfaces. Tyrocidines (Trcs), antimicrobial peptides produced by
Bacillus aneurinolyticus, are cyclodecapeptides with a broad spectrum of activity against Grampositive
bacteria, fungi, yeasts and the human malaria parasite, Plasmodium falciparum. The aim
of this study was to determine the antimicrobial activity of surfaces treated with a tyrocidine extract, under which conditions the activity remained stable and to look into possible
applications of these peptide-treated surfaces.
The study focussed on different solid surfaces namely mixed cellulose, polyvinylidene fluoride,
polycarbonate, cellulose acetate, cellulose (paper)(CL) and high density cellulose packing
material (HDC), as a pilot study to assess the antimicrobial activity of Trc and gramicidin S (GS)
treated solid surfaces. Peptide desorption and subsequent analysis by mass spectrometry was
used to confirm the presence and integrity of the Trcs adsorbed. Scanning electron microscopy
was utilised to show that the adsorbed peptides did not affect the structural integrity of the treated
filters. However, it was shown that the adsorbed peptides changed the hydrophobic/hydrophilic
character by means of a wettability assay. A cell viability assay and erythrocyte assay were developed from existing methodologies to
determine the biological activity of the AMP-functionalised polymeric material. Seven of the
AMP treated solid surfaces showed antimicrobial activity when challenged with >105
Micrococcus luteus cells/cm2. Although the polycarbonate filter lost antimicrobial activity at the high cell concentrations, it was shown to have potent antimicrobial activity at lower cell
concentrations. Complete inhibition of M. luteus growth was observed for both the gramicidin S
and tyrocidine extract treated high density cellulose and cellulose filters.
Stability tests showed that the tyrocidines remained adsorbed to cellulose filters and biologically
active when exposed multiple water washes, water washes at different temperatures (25°C -
100°C) and pH changes (pH 1-12). The antimicrobial activity was only affected after exposure to
the water wash of pH 13 which is possible due to susceptibility of the CL filters to high pH
solvents. A preliminary study on the effect of Trcs treated CL filters on the sterilization,
germination and effect on tomato seedlings was conducted. It was found that Trcs had no effect
on the germination and did not fully sterilise the seeds or environment against fungi. However, it
was observed that 5 μg/mL Trcs treated filters promoted root length opposed to the toxic effect
seen with filters treated with higher Trc concentrations. It is hypothesised that Trcs prefer to bind to hydrophilic surfaces exposing the hydrophobic
residues and the cationic residue of the peptide to interact with the bacterial membrane to elicit
its antimicrobial response. The exposed residues contain some of the hydrophobic residues and
the cationic Orn9/Lys9, which are crucial to the antimicrobial activity of the peptides.
Hydrophobic interaction is particularly important for the haemolytic activity which is currently
the only viable method of detection of the adsorbed Trcs. Trcs also have a preference for
adsorption onto cellulose and cellulose analogues which points to possible application in
protective food wrapping and wood surface protection.
Trcs maintains its antimicrobial activity regardless of adsorption to solid surfaces. It can
therefore be concluded that Trcs treated solid surfaces hold great potential in preventing the
initial bacterial colonization and subsequent biofilm formation. Antimicrobial peptide enriched
solid surfaces can thus be developed and tailored to a specific application such as filters,
catheters and packaging materials. / AFRIKAANSE OPSOMMING: Biovervuiling is die aanhegting en vorming van biofilms met negatiewe gevolge soos
aanhoudende na-oes infeksies, infeksies op mediese inplantings en voortdurende oppervlak
besoedeling van voedselverwerkings fabrieke. Die probleem lê grotendeels by die weerstand wat
ontwikkel word teen konvensionele behandelings as gevolg van die vorming van volwasse
biofilms. Die fokus het gevolglik verskuif vanaf die verwydering van biofilms na die
voorkoming van aanvanklike aanhegting van organismes aan oppervlaktes. Dit behels die
gebruik van antimikrobiese oppervlaktes wat of 'n inherente antimikrobiese aktiwiteit het, bv.
sekere metale óf oppervlaktes wat aangepas is deur die aanhegting van antimikrobiese middels.
Die aanhegting van antimikrobiese agente kan of deur kovalente binding óf adsorpsie plaasvind,
afhangende van die beoogde gebruik van die oppervlak, sowel as die metode van werking van die
antimikrobiese agent. Antimikrobiese peptiede (AMPe) is alomteenwoordig in die natuur, is
geneig om 'n breë spektrum van aktiwiteit te hê, is baie stabiel en het getoon dat aktiwiteit in
stand gehou word wanneer dit kovalent gebind word op soliede oppervlaktes. Tirosidiene (Trcs),
antimikrobiese peptiede wat deur Bacillus aneurinolyticus geproduseer word, is siklodekapeptiede
met 'n breë spektrum van aktiwiteit teen Gram-positiewe bakterieë, swamme, giste
en die menslike malaria parasiet Plasmodium falciparum. Die doel van hierdie studie was om die antimikrobiese aktiwiteit te bepaal van oppervlaktes wat met 'n tirosidien ekstrak behandel is, te
bepaal onder watter omstandighede die aktiwiteit stabiel bly en om te soek na moontlike
toepassings van hierdie peptied-behandelde oppervlaktes.
Die studie het gefokus op verskillende soliede oppervlaktes naamlik gemengde sellulose,
polyvinylidene fluoried, polikarbonaat, sellulose asetaat, sellulose (papier)(CL) en 'n hoë digtheid
sellulose verpakkings materiaal (HDC), as 'n loodsstudie om die antimikrobiese aktiwiteit van
die Trcs en gramisidien S (GS) behandelde soliede oppervlaktes te ondersoek. Peptied-desorpsie
en daaropvolgende ontleding deur massaspektroskopie is gebruik om die teenwoordigheid en
integriteit van die geadsorbeerde Trcs te bevestig. Skandering elektronmikroskopie is gebruik om
aan te toon dat die geadsorbeerde peptiede geen invloed op die strukturele integriteit van die
behandelde filters het nie. Daar is egter getoon dat die geadsorbeerde peptiede die hidrofobiese /
hidrofiliese karakter verander. „n Lewensvatbaarheid selgebaseerde toets en eritrosiet toets is ontwikkel uit bestaande metodes om die biologiese aktiwiteit van die AMP-gefunktionaliseerde polimeriese materiaal te bepaal.
Sewe van die AMP behandel soliede oppervlaktes het antimikrobiese aktiwiteit getoon wanneer
dit met > 105 Micrococcus luteus selle/cm2 gedaag is. Hoewel die polikarbonaat filter
antimikrobiese aktiwiteit met hoë sel konsentrasies verloor het, is dit getoon dat dit wel
uitgeproke antimikrobiese aktiwiteit het teen laer konsentrasies selle. Volledige inhibisie van M.
luteus groei is waargeneem vir beide die hoë digtheid sellulose en sellulose filters wat met GS en
tirosidien ekstrak behandel is.
Stabiliteit toetse het getoon dat die tirosidiene geadsorbeer en biologies aktief op sellulose filters
bly nadat dit blootgestel is aan verskeie water was-stappe, waterwasse by verskillende
temperature (25 °C -100 °C) en pH veranderinge (pH 1-12). Die antimikrobiese aktiwiteit was
net beïnvloed ná blootstelling aan die water met 'n pH 13, wat moontlik is te danke aan die
vatbaarheid van die CL filters by hoë pH oplosmiddels is. 'n Voorlopige studie is gedoen om die
uitwerking van Trcs behandelde CL filters op die sterilisasie, ontkieming en tamatiesaailinge te
bepaal. Daar is gevind dat Trcs geen effek op die ontkieming het nie, maar dat dit nie volledig
die sade en omgewing steriliseer vir fungiese groei nie. Daar is egter waargeneem dat 5 μg/mL Trcs behandelde filters wortel lengte van die saailinge bevorder teenoor die giftige uitwerking
soos waargeneem vir die filters wat met hoër konsentrasies Trcs behandel is.
Dit word gepostuleer dat Trcs verkies om aan hidrofiliese oppervlaktes te bind wat die van die
hidrofobiese aminosure en die kationiese residu van die peptied blootstel om aan die bakteriële
membraan te bind om gevolglik antimikrobiese reaksie te ontlok. Die blootgestelde deel bevat
sommige van die hidrofobiese residue en positiewe Orn9/Lys9 wat noodsaaklik vir die
antimikrobiese aktiwiteit van die peptiede. Die hidrofobiese interaksies is veral belangrik vir die
hemolitiese aktiwiteit wat tans die enigste bruikbare metode van opsporing van die
geadsorbeerde Trcs is. Trcs het ook 'n tendens vir adsorpsie op sellulose en sellulose analoë wat
dui op die moontlike toepassing in beskermende voedselverpakking en die beskerming van
houtoppervlaktes. Trcs handhaaf hul antimikrobiese aktiwiteit, ongeag van adsorpsie aan soliede
oppervlaktes. Dit kan dus afgelei word dat Trcs-behandelde soliede oppervlaktes die potensiaal
het om die aanvanklike kolonisasie van bakterië te voorkom en die daaropvolgende biofilm
vorming. Antimikrobiese peptied verrykde soliede oppervlaktes kan dus ontwikkel en aangepas
word vir gebruik in spesifieke toepassing soos in filters, kateters en verpakkingsmateriaal.
|
6 |
Tyrocidines, cyclic decapeptides produced by soil bacilli, as potent inhibitors of fungal pathogensTroskie, Anscha Mari 04 1900 (has links)
Thesis (PhD)--Stellenbosch University, 2014. / ENGLISH ABSTRACT: The global rise in microbial resistance, ranging from the agricultural industry to the medical
sector, has created the urgent need for novel or supplementary antibiotics. Antimicrobial
peptides or “nature’s antibiotics” may be the answer to this major problem. In this study a group
of antimicrobial peptides, cyclic decapeptides named tyrocidines, produced by the soil bacterium
Bacillus aneurinolyticus, was investigated for their antifungal activity, possible mode of
antifungal action and potential applications.
The study illustrated that the tyrocidines have significant antifungal activity against a range of
phytopathogens, including Fusarium solani and Botrytis cinerea, as well as the human pathogen
Candida albicans. The activity of the tyrocidines is influenced by the identity of both the target
organism and the media environment. Further evidence was obtained in support of the
hypothesis that the tyrocidines are extremely sensitive to their environmental conditions and that
they tend to self-assemble to form oligomers. The assessment of a small tyrocidine library and
analogues, comprised of eight peptides, revealed no overt structure-activity relationships against
fungal pathogens, except for the importance of a tyrosine residue. This indicated an important
role for the conserved sequence of the tyrocidines, NQYVOLfP, together with the tendency of
the tyrocidines to oligomerise into higher-order active structures in their antifungal activity.
The tyrocidines were found to be membrane active toward the fungal pathogens. However,
supporting evidence was also obtained for additional mode(s) of antifungal action for the
tyrocidines which inter alia induces morphological abnormalities in filamentous fungal target
cells. Furthermore, the results also indicated that the membrane activity of the tyrocidines may
be influenced by additional factors to that of the composition of the target cell membrane, for
instance components of the fungal cell wall. This investigation also indicated the significant potential of the tyrocidines to be developed for
the commercial sector. The potent activity of the tyrocidines against agronomically important
phytopathogens (significantly higher than the commercial fungicide bifonazole) together with
their relative salt stability bodes well for their development as bio-fungicides for the agricultural
sector. The tyrocidines also exhibited an overt sinergistic effect on the in vitro candidacidal
activity of two key antifungal drugs, caspofungin and amphotericin B. Furthermore, tyrocidine A
and caspofungin exhibited synergistic activity in vivo which had a significant positive effect on
the survival of C. albicans infected Caenorhabditis elegans. Latter results highlighted their
potential to serve as candidates for combinatorial treatment in the medical industry. / AFRIKAANSE OPSOMMING: Die globale verskynsel van mikrobiese weerstand, wat strek vanaf die landbou sektor tot in die
mediese bedryf, het ’n dringende behoefte vir die ontwikkeling van nuwe antmikrobiese middels
geskep. Antimikrobiese peptiede of “die natuur se antibiotika”, kan moontlik die antwoord op
hierdie ernstige problem wees. Tydens hierdie studie is ‘n groep sikliese antimikrobiese
peptiede, naamlik die tirosidiene wat deur die grondbakterium Bacillus aneurinolyticus
geproduseer word, vir hulle antifungiese aktiwiteit, hulle moontlike meganisme(s) van
antifungiese werking en hulle potensiёle aanwendings bestudeer.
Hierdie studie het getoon dat die tirosidiene uitsonderlike antifungiese aktiwiteit teen ‘n reeks
fitopatogene, insluitend Fusarium solani en Botrytis cinerea, asook teen die mens patogeen
Candida albicans het. Die aktiwiteit van die tirosidiene is deur beide die identiteit van die
teikenorganisme sowel as die mediumomgewing beїnvloed. Daar is ook verdere bewyse verkry
wat die hipotese dat tirosidiene uiters sensitief is tot hulle omgewing en dat hulle neig om te
oligomeriseer, ondersteun. Die studie van die klein tirosidien-biblioteek, saamgestel uit agt
tirosidiene en analoё, het geen ooglopende struktuur-aktiwiteit verwantskappe opgelewer nie,
behalwe vir die oёnskynlike invloed van die tirosien-residu. Laasgenoemde het die belangrikheid
van die gekonserveerde aminosuurvolgorde van die tirosidiene, NQYVOLfP, asook die neiging
van tirosidiene om hoё-orde aktiewe strukture te vorm deur self-verpakking, beklemtoon.
Tydens die studie is daar gevind dat die tirosidiene membraan-aktiewiteit toon teenoor fungiese
patogene. Daar is egter ook goeie bewyse vir alternatiewe meganisme(s) van antifungiese
werking, wat ondermeer tot morfologiese abnormaliteite in filamentagtige fungi-teikenselle lei,
vir die tirosidiene verkry. Die resultate het verder ook daarop gewys dat die membraan-aktiwiteit van die tirosidiene ook deur ander faktore, soos deur komponente van die fungiese selwand, en
nie net deur die samestelling van die fungiese membraan beїnvloed word nie.
Hierdie ondersoek het ook die aansienlike potensiaal van die tirosidiene vir kommersiёle
ontwikkeling en gebruik uitgelig. Die merkwaardige aktiwiteit van die tirosidiene teen
fitopatogene van agronomiese belang (wat selfs beter as diè van die kommersiёle swamdoder
bifonazole was) tesame met die relatiewe sout stabiliteit van die tirosidiene, is belowende tekens
om die tirosidiene as bio-swamdoders vir die landbou sektor te ontwikkel. Die tirosidiene het
ook ‘n uitgesproke sinergistiese effek op die in vitro candidasidiese aktiwiteit van twee sleutel
antifungiese middels, caspofungin en amphotericin B, getoon. Verder is daar in vivo sinergistiese
aktiwiteit gewys deur die kombinasie van tirosidien A en caspofungin wat ’n beduidende
positiewe effek op die oorlewing van C. albicans geïnfekteerde Caenorhabditis elegans gehad
het. Laasgenoemde dui op die potensiaal van die tirosidiene om in die mediese bedryf as
kandidate vir kombinasie-behandeling te dien.
|
Page generated in 0.0351 seconds