1,721,214 research outputs found
Environmental factors modify carbon nutritional patterns and niche overlap between Aspergillus flavus and Fusarium verticillioides strains from maize.
Full text linkThis study examined the utilization patterns of key carbon sources (CS, 24: including key sugars, amino acids and fatty acids) in maize by strains of Aspergillus flavus and Fusarium verticillioides under different water activity (aw, 0.87–0.98 aw) and temperature (20–35 °C) values and compared the niche overlap indices (NOI) that estimate the in vitro CS utilization profiles [Wilson, M., Lindow, S.E., 1994. Coexistence among epiphytic bacterial populations mediated through nutritional resource partitioning. Applied and Environmental Microbiology 60, 4468–4477.]. The ability to grow in these key CS in minimal media was studied for 120 h in 12 h steps. The NOI was calculated for inter-species (F. verticillioides–A. flavus) and for intra-species (A. flavus–A. flavus) using CS utilization patterns over the range of interacting environmental conditions. 30 °C, over the whole aw range examined, was found to be optimal for utilization of the maximum number of CS by A. flavus. In contrast, for F. verticillioides this was more so at 20 °C; 25 °C allowed a suboptimal usage of CS for both species. NOIs confirmed the nutritional dominance of A. flavus at 30 °C, especially at lower aw levels and that of F. verticillioides at 20 °C, mainly at 0.95 aw. In other conditions of aw, based on CS utilization patterns, the data indicated that A. flavus and F. verticillioides occupied different ecological niches. The variability in nutritional sources utilization between A. flavus strains was not related to their ability to produce aflatoxins (AFs). This type of data helps to explain the nutritional dominance of fungal species and strains under different environmental conditions. This could be useful in trying to find appropriate natural biocontrol microorganisms to compete with these mycotoxigenic species
Effect of solute and matric potential on in vitro growth and sporulation of strains from a new population of Aspergillus flavus isolated in Italy.
No full textThe effect of temperature and different solute (Ψs) and matric potentials (Ψm) on growth and sporulation of three aflatoxigenic strains of Aspergillus flavus isolated from contaminated maize in northern Italy was determined. The Ψs of maize-based media were modified ionically (NaCl) and non-ionically (glycerol) and the Ψm with PEG 8000 in the range −1.4 to −21.0 MPa at 25 and 30 °C. Both temperature and Ψs/Ψm stress had statistically significant effects on growth rates of the three strains. Faster growth occurred at 30 °C and −1.4 and −2.8 MPa. A. flavus strains were more sensitive to Ψm than Ψs stress with limits of −9.8 MPa and −14 to−18 MPa, respectively. Sporulation was significantly influenced by Ψs potential, solute type and temperature. This suggests that these aflatoxigenic strains of A. flavus isolated from aflatoxin-contaminated maize are probably able to colonise crop debris rapidly at prevailing temperatures and water stress conditions. This type of information on the ecology of aflatoxin producing A. flavus strains isolated in Italy will contribute to the development of a systems model to predict their activity in crop residue and colonisation of maize grain
Application of electronic nose technology for the detection of fungal contamination in library paper
No full textStudies were carried out in vitro on a cellulose based agar at two water activities (a(w),0.975,0.995) and on three types of paper at two relative humidities (75, 100% RH) for the potential for differentiation of contamination and colonisation by Aspergillus terreus, A. holandicus and Eurotium chevalieri. In vitro studies showed that conducting polymer sensor array gave different responses to each of these species when grown on cellulose agar at both a, levels. Discriminant function analyses of the data showed differentiation of the controls from the spoilage fungi. Cluster analysis gave a significant (P = 0.05) separation of the control and each spoilage fungus. In situ studies on three types of paper showed that using natural substrates the volatile patterns produced by each of these fungi was different from each other and from the control. The results obtained were better at the higher humidity. The three paper types could be successfully differentiated into clusters. For a single paper type, differentiation of controls from spoilage fungal treatments was better at the higher humidity. This study has shown that this technology has potential for the early detection of fungal contamination in library materials and archives for the improved protection of cultural heritage. (C) 2004 Elsevier Ltd. All rights reserved
In vitro impact on growth, fumonisins and aflatoxins production by Fusarium verticillioides and Aspergillus flavus using anti-fungal compounds and a biological control agent
No full textThe temporal efficacy of three different chemical fungicides (Folicur®, Proline®, Sportak 45EW®) and a biocontrol bacterium (Serenade, B. subtilis) in reducing growth and toxin production by isolates of F. verticillioides and A. flavus was studied in vitro under different water activity regimes (0.99, 0.98 and 0.95). All the fungicides significantly inhibited mycelial growth compared with the control; the most effective treatment, both against F.
verticillioides and A. flavus, was Sportak 45EW® (approx. 99%). The inhibitory effect of all fungicides generally improved with increasing concentration. Serenade always decreased fungal growth, with optimal results at concentrations of 104 and 106 (70‒75% reduction). All the fungicide treatments resulted in a significant reduction in both FB1+FB2 and AFB1 production when compared to the control, at the end of the incubation period and with the
2 concentrations used (approx. 99%). A threshold concentration inoculum of at least 104 CFUs of B. subtilis per g
was required to achieve a significant control of mycotoxin production. Sportak 45EW® and Serenade gave the best
control of mycotoxin production with a reduction of 95% compared to the controls. Use of Serenade in the field
should include due consideration to its sensitivity to low water activities, when compared to the target pathogens
Detection and discrimination between ochratoxin producer and non-producer strains of Penicillium nordicum on a ham-based medium using an electronic nose
Full text linkThe aim of this work was to evaluate the potential use of qualitative volatile
patterns produced by Penicillium nordicum to discriminate between ochratoxin A
(OTA) producers and non-producer strains on a ham-based medium. Experiments were
carried out on a 3% ham medium at two water activities (aw ; 0.995, 0.95)
inoculated with P. nordicum spores and incubated at 25°C for up to 14days.
Growing colonies were sampled after 1, 2, 3, 7 and 14days, placed in 30-ml
vials, sealed and the head space analysed using a hybrid sensor electronic nose
device. The effect of environmental conditions on growth and OTA production was
evaluated based on the qualitative response. However, after 7days, it was
possible to discriminate between strains grown at 0.995 aw, and after 14days,
the OTA producer and non-producer strain and the controls could be discriminated
at both aw levels. This study suggests that volatile patterns produced by P.
nordicum strains may differ and be used to predict the presence of toxigenic
contaminants in ham. This approach could be utilised in ham production as part
of a quality assurance system for preventing OTA contaminatio
A development of a molecularly imprinted polymer: Specific for ochratoxin A: Theoretical and sensor applications
No full textIn this work the development of two molecularly imprinted polymers, specific
for ochratoxin A, is presented. Ochratoxin A is produced by several
Aspergillus and Penicillium species and is common in cereals and other
starch rich foods and has also been found in coffee, dried fruits, wine, beer
and meats. It demonstrates potent teratogenic, immunosuppressive,
mutagenic and carcinogenic properties. The toxin is also linked to Balkan
Endemic Nephropathy, a chronic kidney disease found in South-Eastern
Europe. Due to this the European Union has set limits on foodstuffs ranging
between 2-10 ng g-1. Therefore the requirement of a simple and inexpensive
biosensor to monitor this legislation is a necessity. Currently detection is
performed by chromatographic methods such as HPLC, and by ELISA
formats.
In this work two polymeric materials, rationally designed by computational
modelling and synthesised using molecular imprinting, are studied. The
modelling is complimented with a Nuclear Magnetic Resonance (NMR) study.
The first polymer (Polymer A) consisted of 1 mol of acrylamide and 1 mol of
methacrylic acid to 1 mol of template. This material demonstrated an unusual
binding mechanism, working solely in aqueous solvents. A theoretical
mechanism for this binding is presented and discussed.
The second polymer, again rationally designed, but under different conditions,
consisted of 1 mol of N,N- diethylamino ethyl methacrylate (DEAEM) to 1 mol
of template. This polymer demonstrated high affinity for the template in
acetonitrile.
Polymer A is used in combination with an ion-exchange SPE protocol
(developed for this purpose) for the extraction of OTA from maize.
Both polymer compositions are used in development of a MIP membrane
optical sensor, with partial success seen in the detection of OTA in grape juice
and white wine
Development of life marker chip technology for in-situ life detection on Mars
Full text linkThe European Space Agency (ESA) is currently developing its flagship Life Detection Mission, ExoMars, which is scheduled to fly to Mars in 2013. The primary goal of this mission is to compliment the Phoenix NASA mission in confirming the presence of organic material on Mars, and, for the first time, analyse this organic material to determine the presence of organic species indicative of presence of past or present Life. One of the proposed Life detection technologies is the Life Marker Chip (LMC), which uses immunoassays with fluorescent readout to detect small organics and proteins in a microarray format within microfluidic channel structures. This PhD thesis encompasses the work done by the author on the development of the SMILE LMC during the period prior to, and during part of the first phase of, the Life Marker Chip Technology Readiness Level Upgrade Study funded by ESA from 2005 and 2007. Cont/d
Novel food applications of electronic nose technology for detection of spoilage fungi
Full text linkThis work investigated the potential use of the electronic nose ( e-nose) for the rapid
and early detection of fungal spoilage in intermediate moisture bakery products. Four
xerophilic Eurotium spp., Penicillium chrysogenum and Wallemia sebi were grown
on 2% wheat meal agar (WMA, 0.95 aw) at 25°C. Discrimination between the fungal
species and the control media based on their volatile patterns was possible after 48h,
using the Bloodhound BHl 14 e-nose. Volatile patterns produced by four Eurotium
spp. and the Penicillium sp. were also investigated on WMA at different water
activities (0.95, 0.90 and 0.85). Enzyme assays using p-nitrophenyl substrates were
used as an indicator of spore germination and growth, and compared with volatile
patterns and growth rates. Only three of the seven enzymes assayed were found to
change significantly i.e. N-acetyl-P-D-glucosaminidase, a-D-galactosidase and P-Dglucosidase. Earlier detection and differentiation of the control blanks and the fungal
species were achieved after 48h incubation, using the e-nose when compared to
enzyme assays.
In vitro study of volatile profiles from mycotoxigenic (Aspergillus flavus, A.
ochraceus and W. sebi) and non-mycotoxigenic (A. niger and P. chrysogenum) fungi
grown on WMA media demonstrated that differentiation of control blank media from
the spoilage fungi was possible after 72h growth. Work on different mycotoxigenic
and non-mycotoxigenic strains of Fusarium moniliforme and F. proliferatum showed
that the e-nose could discriminate between the control blanks and the different strains
after 48h growth. For all these studies the same three enzyme activities were found to
be significant as in the previous work. Furthermore, the e-nose could detect fungal
spoilage earlier than the enzyme assays.
Volatile patterns produced by two Eurotium spp. and P. chrysogenum colonising a
bread analogue modified to 0.95 aw at 25°C could be discriminated from the
uninoculated bread after 40h incubation. This suggested that e-nose systems could be
an earlier detection tool than enzyme assays. Furthermore, the same enzyme
activities were found to be predominant as that observed for in vitro studies. E. chevalieri and P. chrysogenum were used to determine the limit of detection on a
bread analogue (0.95 aw) using three inoculum concentrations (102
, 104 and 106
spores mr1
). The initial spore concentration of 106 spores mr
1 treatments and the
uninoculated bread analogue could be discriminated after 24h incubation. In another
study, the volatile patterns produced by two Eurotium spp. and P. chrysogenum in
the presence of potassium sorbate were measured. The uninoculated bread substrate
and those colonised by the spoilage fungi could be discriminated after 48h growth.
The study was repeated using calcium propionate and differentiation could be
achieved only after 24h incubation. In the final study, volatile patterns produced by
two Eurotium spp. and P. chrysogenum growing on natural bread substrate could be
differentiated along with the uninoculated bread after 24h growth prior to any visible
signs of growth. Overall, this study suggests that for the first time e-nose systems
could be used to detect qualitative changes in volatile patterns for early and rapid
detection of activity of the spoilage moulds in bakery products.Ph
Optimization of bioprocess design for pharmaceutical metabolites and enzymes
Full text linkThis study examines the effect of ecophysiology on growth of cells and production of enzymes and secondary metabolites produced by the fungi Aspergillus niger (lysozyme) and a Phoma sp. (squalestatin S1). The effect of interactions of water activity (aw) (0.99-0.90), temperature (20, 30 and 35°C) and modifying aw solute (glycerol, NaCl) on growth and sporulation of a wild type strain of Aspergillus niger (W) and two genetically engineered lysozyme producing strains (L11, B1) was examined for the first time. Maximum growth rates were achieved for both strains (L11 and B1) under moderate aw levels. Optimum conditions for growth of strain L11 were estimated by means of contour plot surfaces and found to be 0.965 aw with glycerol as a solute at 35ºC (10.5 mm day-1). A model combining the effect of aw and temperature on growth of strains of Aspergillus niger, and comparison with data on food spoilage moulds in the literature was developed. The growth of two strains of A. niger, as a function of temperature (25-30oC) and aw (0.90-0.99) was developed. The estimation of the minimum aw (awmin) and optimal aw (awopt) levels were in accordance with data in the literature for a range of other Aspergillus and related species, regardless of the solutes used for aw modification. A central composition design was used to describe the effects of water activity (aw, 0.98, 0.97 and 0.96), inoculum size (2.7x105, 2.7x104 and 2.7x103 spores ml-1), and three autoclaving procedure (A = all components autoclaved together, B = medium autoclaved + maltose filtered and, C = medium autoclaved + maltose & soya milk filtered) on the production of lysozyme by two genetically-engineered strains of Aspergillus niger (B1 and L11) in a liquid culture fermentation. Although both strains produced similar lysozyme concentrations (15 mg l-1), different production patterns were found under the experimental conditions. However, strain B1 produced relatively higher amounts of lysozyme under water stress (0.96 aw) with all the substrates autoclaved together. Subsequently, a central composition design was used to investigate: different immobilized polymer types (alginate and pectate), polymer concentration (2 and 4% (w/v)), inoculum support ratios (1:2 and 1:4) and gel-inducing agent concentration (CaCl2, 2 and 3.5% (w/v)) on lysozyme production. Overall immobilization in Ca-pectate resulted in higher lysozyme production compared to immobilization in Ca-alginate. Similar effects were observed when the polymer concentration was reduced. A 13 fold higher lysozyme production was achieved with Ca-pectate in comparison to Ca-alginate (20-23 and 0.5-1.7 mg l-1 respectively). Polymer modifications also significantly affected the final pH and aw of the immobilized cell fermentation. The aw factor is a very significant parameter in the immobilization design. A combined statistical methodology of orthogonal design L27(313) and surface response methodology was applied to optimize the composition and concentration of a liquid fermentation medium for the production of squalestatin S1 by a Phoma species. Confirmatory experiments of the optimal medium composition produced average concentrations of 434 mg l 1 in five days fermentation at 25oC. This represented an improvement over 60% of the maximum concentration achieved in the initial experiment and a two-fold higher productivity in comparison with reported productivities of S1 in liquid fermentations with different fungal species. Different liquid height and column diameter (HL/Hr) ratios 3.7, 7.4 and 11.4 were studied in a bubble column (Dr=0.07 m) with a porous plate gas distributor, to find the effect on the gas hold up, power consumption (PG/VL) and volumetric mass transfer coefficient, kLa performance, under different superficial gas velocities calculated from the liquid properties and flow rates (2, 4, 6 and 8 l min-1) and temperatures (15, 25 and 30oC). Two kLa models were proposed based on the geometrical ratio (HL/Dr) and superficial gas velocity (m s-1) (R2=0.951), and power consumption (PG/VL) (R2=0.950). A free cell fermentation was performed in the bubble column, ratio (HL/Dr)= 3.7 and superficial gas velocity U= 0.120 m s-1, at 25oC. The S1 production reached a level of 420 mg l 1. The bioreactor scale up succeeded in maintaining the high S1 concentration obtained in our previous work 434 mg l 1 in Erlenmeyer flasks but in a shorter time. A Plackett-Burman design was used to improve the S1 produced by different immobilized designs. The immobilized cell fermentation design considered: polymerization with alginate and polygalacturonate and copolymerization, polymer concentration (alginate 3, 3.5 and 5 % w/v and pectate 4, 6 and 8 % w/v), 0.98, 0.96 and 0.94 aw levels, inoculum levels of 10, 20 and 30 % wt. v/v, gel-inducer (CaCl2) 3, 4 and 5 % w/v, gel-reinforce agent 0, 0.75 and 1.5 g l-1, air flow 4, 6 and 8 l min-1. Production of S1 reached levels of 883 mg l-1 which represent a 34 % improvement over the 660 mg l 1 produced in a stirred tank bioreactor (STR) with a free cell fermentation
Microbial and non-microbial volatile fingerprints: Potential clinical applications of electronic nose for early diagnoses and detection of diseases
Full text linkThis is the first study to explore the potential applications of using qualitative volatile fingerprints (electronic nose) for early detection and diagnosis of diseases such as dermatophytosis, ventilator associated pneumonia and upper gastrointestinal cancer. The investigations included in vitro analysis of various dermatophyte species and strains, antifungal screening, bacterial cultures and associated clinical specimens and oesophageal cell lines. Mass spectrometric analyses were attempted to identify possible markers.
The studies that involved e-nose comparisons indicated that the conducting polymer system was unable to differentiate between any of the treatments over the experimental period (120 hours). Metal oxide-based sensor arrays were better suited and differentiated between four dermatophyte species within 96 hours of growth using principal component analysis and cluster analysis (Euclidean distance and Ward’s linkage) based on their volatile profile patterns. Studies on the sensitivity of detection showed that for Trichophyton mentagrophytes and T. rubrum it was possible to differentiate between log3, log5 and log7 inoculum levels within 96 hours. The probabilistic neural network model had a high prediction accuracy of 88 to 96% depending on the number of sensors used.
Temporal volatile production patterns studied at a species level for a Microsporum species, two Trichophyton species and at a strain level for the two Trichophyton species; showed possible discrimination between the species from controls after 120 hours. The predictive neural network model misclassified only one sample. Data analysis also indicated probable differentiation between the strains of T. rubrum while strains of T. mentagrophytes clustered together showing good similarity between them.
Antifungal treatments with itraconazole on T. mentagrophytes and T. rubrum showed that the e-nose could differentiate between untreated fungal species from the treated fungal species at both temperatures (25 and 30°C). However, the different antifungal concentrations of 50% fungal inhibition and 2 ppm could not be separated from each other or the controls based on their volatiles.
Headspace analysis of bacterial cultures in vitro indicated that the e-nose could differentiate between the microbial species and controls in 83% of samples (n=98) based on a four group model (gram-positive, gram-negative, fungi and no growth). Volatile fingerprint analysis of the bronchoalveolar lavage fluid accurately separated growth and no growth in 81% of samples (n=52); however only 63% classification accuracy was achieved with a four group model. 12/31 samples were classified as infected by the e-nose but had no microbiological growth, further analysis suggested that the traditional clinical pulmonary infection score (CPIS) system correlated with the e-nose prediction of infection in 68% of samples (n=31).
No clear distinction was observed between various human cell lines (oesophageal and colorectal) based on volatile fingerprints within one to four hours of incubation, although they were clearly separate from the blank media. However, after 24 hours one of the cell lines could be clearly differentiated from the others and the controls. The different gastrointestinal pathologies (forming the clinical samples) did not show any specific pattern and thus could not be distinguished.
Mass spectrometric analysis did not detect distinct markers within the fungal and cell line samples, but potential identifiers in the fungal species such as 3-Octanone, 1-Octen-3-ol and methoxybenzene including high concentration of ammonia, the latter mostly in T. mentagrophytes, followed by T. rubrum and Microsporum canis, were found.
These detailed studies suggest that the approach of qualitative volatile fingerprinting shows promise for use in clinical settings, enabling rapid detection/diagnoses of diseases thus eventually reducing the time to treatment significantly
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