8 research outputs found
Phage Amplification and Immunomagnetic Separation Combined with Targeted Mass Spectrometry for Sensitive Detection of Viable Bacteria in Complex Food Matrices
We
have developed and describe here for the first time a highly
sensitive method for the fast and unambiguous detection of viable <i>Escherichia coli</i> in food matrices. The new approach is based
on using label-free phages (T4), obligate parasites of bacteria, which
are attractive for pathogen detection because of their inherent natural
specificity and ease of use. A specific immunomagnetic separation
was used to capture the progeny phages produced. Subsequently, T4
phage markers were detected by liquid chromatography coupled to targeted
mass spectrometry. Combining the specificity of these three methodologies
is of great interest in developing an alternative to conventional
time-consuming culture-based technologies for the detection of viable
bacteria for industrial applications. First, optimization experiments
with phage T4 spiked in complex matrices (without a phage amplification
event) were performed and demonstrated specific, sensitive, and reproducible
phage capture and detection in complex matrices including LuriaâBertani
broth, orange juice, and skimmed milk. The method developed was then
applied to the detection of <i>E. coli</i> spiked in foodstuffs
(with a phage amplification event). After having evaluated the impact
of infection duration on assay sensitivity, we showed that our assay
specifically detects viable <i>E. coli</i> in milk at an
initial count of â„1 colony-forming unit (cfu)/mL after an 8-h
infection. This excellent detection limit makes our new approach an
alternative to PCR-based assays for rapid bacterial detection
Cytokines secreted by splenocytes from mice given KLH, BLG, Ara h1 or Cry1Ab by the i.p. route.
<p>Splenocytes from BALB/cJ mice after i.p. administration of PBS (white bars), 1 ”g (gray bars) or 100 ”g (black bars) of KLH, BLG, Ara h1 or Cry1Ab were reactivated <i>ex vivo</i> with 50 ”g of the corresponding antigen. Expected results were obtained from positive (ConA) and negative controls (medium alone) (data not shown).</p
Specific IgG1, IgG2a and IgE antibodies induced after i.p. administration of purified KLH, BLG, Ara h1 or Cry1Ab.
<p>Specific IgG1 (âą, left axis), IgG2a (o, left axis) and IgE (*, right axis) antibodies were assayed in sera of individual BALB/cJ mice after two i.p. administrations of 1 (<b>A</b>) or 100 ”g (<b>B</b>) of each protein, without adjuvant. Bars represent the mean of 5 mice per group. Nonspecific binding (NSB) was determined using EIA buffer instead of serum. Limit of detection was determined as the mean of NSB +3Ï<i><sub>n</sub></i><sub>â1</sub>. a p<0.05 when comparing mice receiving protein with mice receiving PBS (not shown), nonparametric test.</p
Metabolic biomarkers identified from discriminant analysis.
<p>Assignment of significant variables explaining the 4 first components displayed by a linear discriminant analysis performed on OSC-PLSâcorrected data corresponding to the late urine collections performed on days 27 and 28.</p
Sandwich immunoassay of Cry1Ab.
<p><b>A.</b> Standard curve obtained with purified Cry1Ab protoxin in sandwich immunoassay using mAb#120 passively adsorbed on microplates as capture antibody and AChE-labeled mAb#95 as tracer. Mean +/â SD is represented. Each point is the result of duplicate measurements, except NSB (EIA buffer alone, nâ=â8). The limit of detection, defined as the lowest concentration of standard Cry1Ab inducing a signal statistically significantly higher than NSB (i.e. mean+3Ï<i><sub>n</sub></i><sub>â1</sub>) is shown in the insert as a black line. <b>B.</b> Extracts from reference maize powders containing MON810 maize mass fraction level of 0.5% (â), 1% (âŒ) or 2.5% (â) (2- to 250-fold dilutions) or standard Cry1Ab (10 ng/mL, 2- to 128-fold dilutions, â) were assayed using this sandwich immunoassay. All dilution points were assayed in duplicate. Results are expressed as mean of absorbance values (mAU at 414 nm) +/â SD. No signal was detected for non-GM reference maize (not shown).</p
Linear discriminant analysis performed on OSC-PLSâcorrected data corresponding to the late urine collections performed on days 27 and 28.
<p>The four LD are highly significant (p<0.0001) and the 3 respective factorial maps are displayed here: 1Ă2 (<b>A</b>), 2Ă3 (<b>B</b>) and 3Ă4 (<b>C</b>). The cultivar names are displayed on the factorial maps with the .2 and .3 suffixes designating the urine collection performed on days 27 and 28, respectively.</p
AâC: Electrophoretic pattern and IgE-binding analysis of protein extracts from MON810 and non-GM maize:
<p>Protein extracts from MON 810 and its conventional counterpart were separated on 12% acrylamide gel and proteins were stained (<b>A</b>). After transfer to PVDF membrane, IgE binding proteins (i.e. allergens) were revealed by western blotting with the sera of 2 maize-allergic patients, i.e. #20770-MH (<b>B</b>) and #19392-CS (<b>C</b>). Specific IgE concentrations (<b>D</b>) in the same sera were determined on GM (open bar) and non-GM (black bar) protein extract coated plates. Bars represent mean+/âSEM obtained for 3 different dilutions of each serum, each assayed in duplicate.</p
Specific IgE and IgG1 antibodies induced after i.g. or i.p. administration of GM vs non-GM maize extracts.
<p>Mice were given protein extracts from MON 810 or non-GM comparator via the i.p. route (100 ”g of protein/mice emulsified with incomplete Freund's adjuvant) on days 1 and 15 (nâ=â8/group) or via the i.g. route (1 mg of protein mixed with 10 ”g of cholera toxin) on days 1, 7, 13, 19 and 25 (nâ=â10/group). Ten mice received PBS via the i.g. route (PBS mice). Specific IgE (<b>A</b>) and IgG1 (<b>B</b>) antibodies were assayed on microtiter plates coated with non-GM (open circles) or MON810 (black symbols) maize protein extracts. For each group, data of individual serum samples collected on day 30 and the corresponding median values are expressed as absorbance values (mAU at 414 nm). Sample dilutions were 1/40 for assays of IgE antibodies, and 1/4000 (i.g. treated groups) or 1/200000 (i.p. treated groups) for assays of IgG1 antibodies.</p