Inactivation of Escherichia coli Population on Fruit Surfaces Using Ultraviolet-C Light: Influence of Fruit Surface Characteristics

Ultraviolet-C (UV-C 254 nm) light is a possible alternative for chemical disinfection of fresh fruits. However, studies on the influence of surface characteristics on the kinetics of UV-C inactivation of microorganisms on fruits are limited. In this study, UV-C inactivation of generic Escherichia coli (ATCC 23716), a nonpathogenic surrogate strain for E. coli O157:H7, was inoculated onto the skin surface intact pear, pear with surface wounds, and the skin surface of intact peach. Disc shaped (0.057 m diameter?×?0.01 m height) fruit surface were exposed at room temperature to UV-C light ranging from 0 to 7.56?±?0.52 kJ/m² and microbial inactivation kinetics was determined. Maximum reductions of 3.70?±?0.125 log CFU/g were achieved for E. coli on intact pear surfaces (P?<?0.05), with lesser reduction on wounded pear (3.10?±?0.329 log CFU/g) and peach surfaces (2.91?±?0.284 log CFU/g) after 4 min UV-C exposure at 7.56 kJ/m² UV. The Weibull scale factor (α) values of UV-C inactivation for E. coli on an intact pear surface was 0.001?±?0.0007 min (0.235?±?0.001 kJ/m²), wounded pear surface, 0.003?±?0.001 min (0.240?±?0.002 kJ/m²) and peach surface, 0.004?±?0.0004 (0.241?±?0.0008 kJ/m²). The time required for a 90 % reduction in E. coli cell numbers or the reliable life time (t _R) calculated with the Weibull model for intact pear surfaces (0.019?±?0.009 min, 0.268?±?0.017 kJ/m²) was smaller than for wounded pear (0.062?±?0.013 min, 0.348?±?0.024 kJ/m²) and peach surfaces (0.074?±?0.012, 0.371?±?0.012 kJ/m²), suggesting that the wounds on pear surfaces and trichomes (100–1000 μm) on peach surfaces helped to shield and protect microorganisms from UV-C radiation. There was likely a more uniform distribution of bacterial cells onto pear surfaces due to its smaller surface roughness, spreading coefficient, and hydrophobic nature compared to peach. Fourier transform infrared spectroscopy indicate that bacterial membrane damage (phospholipids, protein secondary structures, and polysaccharides) and changes to DNA/RNA in E. coli resulted from UV-C treatment. UV-C can reduce E. coli populations on fresh fruit surfaces, but the efficacy of UV treatment is dependent upon the morphological and surface properties of the fruit and surface integrity.     

Rapid and sensitive detection of Salmonella Typhimurium on eggshells by using wireless biosensors

This article presents rapid, sensitive, direct detection of Salmonella Typhimurium on eggshells by using wireless magnetoelastic (ME) biosensors. The biosensor consists of a freestanding, strip-shaped ME resonator as the signal transducer and the E2 phage as the biomolecular recognition element that selectively binds with Salmonella Typhimurium. This ME biosensor is a type of mass-sensitive biosensor that can be wirelessly actuated into mechanical resonance by an externally applied timevarying magnetic field. When the biosensor binds with Salmonella Typhimurium, the mass of the sensor increases, resulting in a decrease in the sensor's resonant frequency. Multiple E2 phage-coated biosensors (measurement sensors) were placed on eggshells spiked with Salmonella Typhimurium of various concentrations (1.6 to 1.6 × 10(7) CFU/cm(2)). Control sensors without phage were also used to compensate for environmental effects and nonspecific binding. After 20 min in a humidity-controlled chamber (95%) to allow binding of the bacteria to the sensors to occur, the resonant frequency of the sensors was wirelessly measured and compared with their initial resonant frequency. The resonant frequency change of the measurement sensors was found to be statistically different from that of the control sensors down to 1.6 × 10(2) CFU/cm(2), the detection limit for this work. In addition, scanning electron microscopy imaging verified that the measured resonant frequency changes were directly related to the number of bound cells on the sensor surface. The total assay time of the presented methodology was approximately 30 min, facilitating rapid detection of Salmonella Typhimurium without any preceding sampling procedures.     

Detection and differentiation of Salmonella serotypes using surface enhanced Raman scattering (SERS) technique

This research was conducted to prove that developed silver biopolymer nanoparticle substrate for surface enhanced Raman scattering (SERS) technique could detect and differentiate three different serotypes of Salmonella. Nanoparticle was prepared by adding 100 mg of silver nitrate to a 2 % polyvinyl alcohol solution, then adding 1 % trisodium citrate to reduce silver nitrate and produce silver encapsulated biopolymer nanoparticles. Then, nanoparticle was deposited on a stainless steel plate and used as SERS substrate. Fresh cultures of Salmonella typhimurium, Salmonella enteritidis and Salmonella infantis were washed and suspended in 10 mL of sterile deionized water. Approximately 5 μl of the bacterial suspensions were placed on the substrate individually and exposed to 785 nm laser excitation. SERS spectral data were recorded between 400 and 1,800 cm^?1. SERS signals were collected from 15 different spots on the substrate for each sample. PCA model was developed to classify Salmonella serotypes. PC1 identified 92 % of the variation between the Salmonella serotypes, and PC2 identified 6 % and in total 98 % between the serotypes. Soft independent modeling of class analogies of validation set gave an average correct classification of 92 %. Comparison of the SERS spectra of Salmonella serotypes indicated that both isolates have similar cell walls and cell membrane structures which were identified by spectral regions between 520 and 1,050 cm^?1. However, major differences were detected in cellular genetic material and proteins between 1,200 and 1,700 cm^?1. SERS with silver biopolymer nanoparticle substrate could be a promising tool in pathogen detection and it would potentially be used to classify them.     

Analytical performance and characterization of antibody immobilized magnetoelastic biosensors

This article presents the results of an investigation into the enhancement of sensitivity and thermal stability of polyclonal antibody immobilized magnetoelastic biosensors. The Langmuir–Blodgett (LB) monolayer technique was employed for antibody (specific to Salmonella sp.) immobilization on rectangular shaped strip magnetoelastic sensors. Biosensor performance was investigated by exposing to graded concentrations (5 × 10¹–5 × 10⁸ cfu mL⁻¹) of Salmonella typhimurium solutions in a flow through mode. Bacterial binding to the antibody on the sensor surfaces changed the resonance parameters, and these changes were quantified by the sensor’s resonance frequency shift. An increase in the sensitivity from 159 Hz decade⁻¹ for a 2 mm sensor to 246 Hz decade⁻¹ for a 1 mm sensor was observed during the dose–response measurements. The stability of the biosensor was also investigated by storing the biosensor at 25, 45 and 65 °C. The binding activity of the stored biosensor was estimated by measuring the changes in resonance frequency after exposure to the bacterial solutions (10⁹ cfu mL⁻¹). Binding activity was also confirmed by counting bound S. typhimurium cells on the sensor surface using Scanning Electron Microscopy (SEM) micrographs. The results show that at each temperature, the binding activity of the biosensor gradually decreased over the testing period. Degradation of biosensor accelerated at higher storage temperatures. The activation energy of biosensor system degradation was determined to be 7.7 kcal mol⁻¹.     

Bactericidal effects of nonthermal low-pressure oxygen plasma on S. typhimurium LT2 attached to fresh produce surfaces

This work investigates the feasibility of nonthermal low-pressure oxygen plasma on sanitization of spinach, lettuce, tomato and potato surfaces from Salmonella enterica subsp. enterica serovar Typhimurium str. LT2 (Salmonella typhimurium LT2). It was shown that the time of exposure and plasma power density were two critical parameters influencing the bactericidal efficiency. Surface roughness and hydrophobicity did not influence the sanitization of produce. Oxygen plasma was more effective than washing with 3% H₂O₂ on eliminating S. typhimurium LT2 on spinach. Plasma treatment chemically changed a very thin section of tomato wax cuticle layer by oxidation reaction and decomposition of carbon chains, which could readily and completely be removed by water. Overall, this study confirms that nonthermal oxygen plasma can be a new effective method of sanitization for fresh produce.     

Effect of Pulsed Light on Safety and Quality of Fresh Egg Pasta

This study investigated the effect of pulsed light (up to 26.25 J/cm²) on the inactivation of Salmonella enterica and on the eventual occurrence of undesirable changes in the quality of fresh egg pasta just after preparation and during storage at 4 °C. When S. enterica was inoculated on egg pasta surface, a light dose of 0.70 J/cm² sufficed to lower counts by 2.5 log units while 3.50 J/cm² were required for a 3.3 log unit reduction (below detection limit). For S. enterica inoculated in the dough, a light dose of 3.50 J/cm² lowered counts by only 1.0 log unit while 17.50 J/cm² were required for a 3.3 log unit reduction, due to the limited light penetration through egg pasta. At a dose of 1.75 J/cm², pulsed light induced no significant changes in egg pasta appearance, oxidation state and sensory properties. At higher doses, off-flavour formation was detected. Independently of the dose applied, pulsed light did not induce furan formation and promoted an increase in the oxidative stability of egg pasta lipids as well as pigment bleaching during storage. The latter was attributed to the formation of photo-induced non-enzymatic browning products.     

Antimicrobial Polylactic Acid Packaging Films against Listeria and Salmonella in Culture Medium and on Ready-to-Eat Meat

The contamination of Listeria monocytogenes and Salmonella spp. in ready-to-eat (RTE) meat products has been a concern for the meat industry. In this study, edible chitosan-acid solutions incorporating lauric arginate ester (LAE), sodium lactate (NaL), and sorbic acid (SA) alone or in combinations were developed and coated on polylactic acid (PLA) packaging films. Antimicrobial effects of coated PLA films on the growth of Listeria innocua, L. monocytogenes, and Salmonella Typhimurium in a culture medium (tryptic soy broth, TSB) and on the surface of meat samples were investigated. Antimicrobial PLA films containing 1.94 mg/cm² of chitosan and 1.94 μg/cm² of LAE were the most effective against both Listeria and Salmonella in TSB and reduced them to undetectable level (<0.69 log CFU/ml). The same PLA films with LAE significantly (p?L. innocua, L. monocytogenes, and S. Typhimurium on RTE meat during 3 and 5 weeks’ storage at 10 °C, achieving 2–3 log reduction of Listeria and 1–1.5 log reduction of Salmonella as compared with controls. PLA films coated with 1.94 mg/cm² of chitosan, 0.78 mg/cm² of NaL, and 0.12 mg/cm² of SA significantly reduced the growth of L. innocua but were less effective against Salmonella. The combination of NaL (0.78 mg/cm²) and SA (0.12 mg/cm²) with LAE (1.94 μg/cm²) did not generate additional or synergetic antimicrobial effect against Listeria or Salmonella on the meat surface. L. innocua had a similar sensitivity to the film treatments as L. monocytogenes, suggesting that L. innocua may be used as a surrogate of L. monocytogenes for further scaleup and validation studies. The film treatments were more effective against the microorganisms in TSB culture medium than in RTE meat, which suggests that in vivo studies are a necessary step to develop antimicrobial packaging for applications in foods.     

A Biosensor Utilizing l-Glutamate Dehydrogenase and Diaphorase Immobilized on Nanocomposite Electrode for Determination of l-Glutamate in Food Samples

Amperometric biosensor utilizing bienzymatic composition consisting of l-glutamate dehydrogenase and diaphorase for the determination of l-glutamate has been developed. Enzymes were immobilized between chitosan layers onto the surface of planar nanocomposite electrodes consisting of multi-walled carbon nanotubes (diameter?=?60–100 nm; length?=?5–15 μm, 95+?% purity). Linear response was obtained from 10 to 3,495 μM in phosphate buffer solution of pH 9.0 and in the presence of enzyme cofactor NAD⁺ (2 mM) and mediator ferricyanide (5 mM). The limit of detection was 5.4 μM, and sensitivity was found to be 28 nA μM^?1 cm^?2. The biosensor showed a short response time (within 60 s), good storage (no loss of activity for at least 3 months), and operational (response ability above 90 % after 7 days since its first use) stability. Finally, the results obtained from measurements of the food samples were compared with those obtained with an enzymatic–spectrophotometric method and correlated well. Analytical performance of the biosensor indicated that the bienzyme system utilizing diaphorase as a secondary enzyme could be a general basis for other biosensors based on NAD⁺-dependent dehydrogenases.     

Moisture movement in wood polypropylene composites

Moisture movement in an extruded wood polypropylene composite was evaluated by exposure to high humidity and immersion of the material in both fresh and seawater. The saturation moisture content was approximately 20 and 19% when exposed to distilled water and seawater, respectively. The moisture diffusion coefficient (D _m) of thin specimens exposed to high humidity was 3.4?×?10^?8?cm² $ / $ s. The D _m of small cubic specimens with extruded surfaces removed submerged in distilled water and seawater were estimated to be 3.1 and 2.3?×?10^?8?cm² $ / $ s, respectively. Use of these diffusion coefficients overestimates the rate of moisture movement in larger extrusion profiles indicating the role of transport phenomenon other than diffusion.     

Selective detection of Salmonella typhimurium in the presence of high concentrations of masking bacteria

This article presents the results of an investigation into the ability of a magnetoelastic biosensor to detect Salmonella typhimurium, with high specificity, even in the presence of high concentrations of masking bacteria. Magnetoelastic biosensors are mass sensitive devices comprised of a magnetoelastic material that serves as the transducer and bacteriophage as the bio-recognition element. The sensors were tested individually with several different genus bacteria (Salmonella typhimurium, Salmonella entertidis, Escherichia coli O157:H7 and Listeria monocytogenes) to compare the bioprobe’s affinity towards species other than the target analyte. The effect of the presence of one masking bacteria (E. coli) and two masking bacteria (E. coli and L. monocytogenes) in a mixture with S. typhimurium upon the response of the biosensor was studied. It was observed that the response of the sensors followed similar trends; however the sensitivity and the frequency changes were slightly lower for the mixtures. The sensitivity of the sensors exposed to only S. typhimurium was 161 Hz decade⁻¹ and in mixtures with one and two masking bacteria were 131 Hz decade⁻¹ and 127 Hz decade⁻¹, respectively. Binding kinetics studies show that the dissociation constant (K _d) and the binding valency (1/n _H) samples with only S. typhimurium are 149 cfu mL⁻¹ and 2.49, respectively.     

Stimulation of Saccharomyces cerevisiae Cultures by Pulsed Electric Fields

The effects of stimulation of Saccharomyces cerevisiae cells in an aqueous suspension by pulsed electric field (PEF) with electric field strength E?=?20–2,000 V cm^?1 and effective PEF treatment time t _PEF?=?10^?5–1 s were investigated. At relatively high electric field strengths (E?>?1,000 V cm^?1) and moderate times of PEF treatment (t _PEF?>?100 μs), the extraction of ionic components from yeast was observed, which can be related to electroporation of cell membranes. Petri dishes counting revealed dependency of the colony sizes on the time of preliminary fermentation t _f and power consumption W. The “logarithmic” and “saturated” types of electrostimulation were distinguished. At “logarithmic” electrostimulation (10^?7 J mL^?1?W??1 J mL^?1), the viability of yeast cells increased with the increase of power consumption and was higher for longer fermentation (t _f ?=?24 h). However, at “saturated” electrostimulation (10^?1 J mL^?1?W?1 J mL^?1), the viability of yeast cells was noticeably higher for t _f ?=?1 h than for t _f ?=?24 h. The impact of preliminary fermentation time and PEF protocol on biological activity of cells and consumption of nutrients was also discussed.     

Application of Bismuth(III)-Entrapped XO Biosensing System for Xanthine Determination in Beverages

A xanthine biosensor was prepared by electrochemical immobilization of xanthine oxidize enzyme onto carbon paste electrode via entrapment of Bi³⁺. After the optimization of experimental parameters, analytical characteristics were investigated. Two linear ranges between 0.02 and 0.06 and 1–7.5 μM with the equation y?=?93.00x?+?0.12 and y?=?1.07x?+?18.03 with the correlation coefficients of R ²?=?0.9951 and R ²?=?0.9931, respectively, were obtained for this biosensing system. RSD value was calculated for 0.04 μM xanthine (n?=?5) and found as 3.84%. LOD and LOQ values were also calculated and revealed as 1.30?×?10^?8 and 4.3?×?10^?8 M, respectively. Then, this biosensor was applied for xanthine detection in real samples. As a sample treatment, only necessary dilutions were made. Four types of beverages including wine, energy drink, peach, and sour cherry juice were used for this purpose. Obtained recovery values demonstrate that this system is applicable for xanthine detection in real samples without needing any laborious sample pretreatment procedures.     

Glucose Biosensor Based on a Glassy Carbon Electrode Modified with Multi-Walled Carbon Nanotubes-Chitosan for the Determination of Beef Freshness

In this study, the glucose biosensor was developed for the determination of the beef meat freshness based on a glassy carbon electrode (GCE) modified with multi-walled carbon nanotubes (MWCNTs) and chitosan (Chi). Glucose oxidase (GOx) was immobilized onto the MWCNTs-Chi/GCE surface by cross-linking the enzyme through glutaraldehyde with bovine serum albumin (BSA). Glutaraldehyde solution (0.25%, w/w) was also added to prevent enzyme release. The properties of the developed biosensor were characterized with cyclic voltammetry (CV), differential pulse voltammetry (DPV), and electrochemical impedance spectroscopy (EIS) using [Fe (CN)₆]^3?/4?as the supporting electrolyte. The influence of various parameters was investigated, and 0.1 mol L^?1 PBS with pH = 6.4 was chosen as the optimal supporting electrolyte for this experiment. The linear relationship between the current and the concentration of glucose was obtained from 0.2 to 1.2 mmol L^?1, with a detection limit of 0.05 mM at a signal-to-noise ratio of 3 and displayed good linearity (R ² = 0.9902), while the biosensor showed a rapid response to glucose. In addition, the developed glucose biosensor was applied in the determination of glucose in beef as an indicator of beef freshness compared to the total volatile basic nitrogen (TVB-N) method. The glucose level was decreased with increasing beef storage time.     

Evaluation of the Spoilage of Raw Chicken Breast Fillets Using Fourier Transform Infrared Spectroscopy in Tandem with Chemometrics

The aim of this work was to evaluate the potential of Fourier transform infrared (FTIR) spectroscopy as a rapid and accurate technique to detect and predict the onset of spoilage in fresh chicken breast fillets stored at 3, 8, and 30 °C. Chicken breasts were excised from carcasses at 6 h post-mortem; cut in fillets; packed in air; stored at 3, 8, and 30?ºC; and periodically examined for FTIR, pH, microbiological analysis, and sensory assessment of freshness. Partial least squares regression allowed estimations of total viable counts (TVC), lactic acid bacteria (LAB), Pseudomonas spp., Brochothrix thermosphacta, Enterobacteriaceae counts and pH, based on FTIR spectral data. Analysis of an external set of samples allowed the evaluation of the predictability of the method. The correlation coefficients (R²) for prediction were 0.798, 0.832, 0.789, 0.810, 0.857, and 0.880, and the room mean square error of prediction were 0.789, 0.658, 0.715, 0.701, 0.756 log cfu g^?1 and 0.479 for TVC, LAB, Pseudomonas spp., B. thermosphacta, Enterobacteriaceae, and pH, respectively. The spectroscopic variables that can be linked and used by the models to predict the spoilage/freshness of the samples, pH, and microbial counts were the absorbency values of 375 wave numbers from 1,700 to 950 cm^?1. A principal component analysis led to the conclusion that the wave numbers that ranges from 1,408 to 1,370 cm^?1 and from 1,320 to 1,305 cm^?1 are strongly connected to changes during spoilage. These wave numbers are linked to amides and amines and may be considered potential wave numbers associated with the biochemical changes during spoilage. Discriminant analysis of spectral data was successfully applied to support sensory data and to accurately bound samples freshness. According to the results presented, it is possible to conclude that FTIR spectroscopy can be used as a reliable, accurate, and fast method for real time freshness evaluation of chicken breast fillets during storage.     

A maltose,L-rhamnose sensor based on porous Cu foam and electrochemical amperometric i-t scanning method

A maltose, L-rhamnose sensor based on porous Cu foam and electrochemical techniques was investigated in this paper. Cu foam material was prepared and characterized by scanning electron microscopy (SEM). The electro-oxidation reaction process of sweeteners occurred on Cu foam electrode was evaluated by cyclic voltammetry (CV) scanning. At an applied potential of 0.5 V, the linear range for maltose is 0.18–3.47 mM with sensitivity of 1.0492 mA cm^?2 mM^?1. The limit of detection (LOD) was 15.86 μM (S/N?=?3). The linear range for maltose is 0.18–3.47 mM with sensitivity of 0.6881 mA cm^?2 mM^?1. The LOD was 24.18 μM (S/N?=?3). Compared with Cu sheet electrode, Cu foam electrode showed higher current response towards maltose and L-rhamnose, leading to enhanced electrocatalytic activity, higher sensitivity, and lower LOD. Sweetener qualitative discrimination was carried out by stochastic resonance (SR) signal-to-noise ratio (SNR) spectrum eigen peak located noise intensities.     

Simultaneous determination of pyrimethanil,cyprodinil, mepanipyrim and its metabolite in fresh and home-processed fruit and vegetables by a QuEChERS method coupled with UPLC-MS/MS

A QuEChERS procedure for the simultaneous determination of pyrimethanil, cyprodinil, mepanipyrim and its metabolite (M31) in fresh and processed fruit and vegetables was developed using ultra-performance liquid chromatography/tandem mass spectrometry (UPLC-MS/MS). The determination of the four target compounds was achieved in less than 6.0 min using an electrospray ionisation source in positive mode. The limits of detection (LODs) were below 0.4 μg?kg^?1, while the limits of quantification (LOQs) did not exceed 1.5 μg?kg^?1 for all studied matrices. Good linearity of the calibration curves was obtained over the range from 0.002 to 2 mg?kg^?1, with correlation coefficients higher than 0.999. The average recoveries of this method in apple, peach, cabbage and tomato at the five spiked levels (0.002, 0.01, 0.05, 0.20 and 2.0 mg?kg^?1) ranged from 81.5% to 107.3% with relative standard deviations (RSDs) in the range of 1.5–13.9% (n = 5) for all analytes. Residue levels of anilinopyrimidine fungicides in fresh and home-processed apple, peach, cabbage and tomato were also studied. The results indicate that residue levels are significantly reduced following washing, peeling and boiling, and there is no toxic metabolite of mepanipyrim (M31) which is detected during boiling. This study provides a theoretical basis for China to draw up maximum residue limits (MRLs) and protect consumers from the negative health effects of pesticide residues detected in fruit and vegetables.     

Optimization and characterization of pulsed electric field parameters for extraction of quercetin and ellagic acid in emblica officinalis juice

A novel study has been optimized for the application of pulsed electric field (PEF) treatment (varying from 18 to 24 kV cm^?1 for the duration 300–1,000 µs) on fresh emblica juice for extracting quercetin & ellagic acid which are considered as the major secondary metabolites in plant based foods. HPLC–PDA studies showed substantial increase (p < 0.05) in the PEF extracted levels of above metabolites in herb juice. It can be attributed to PEF induced vibrational disruption which increases the metabolic stress leading to emergence of these compounds. Both Raman and FTIR characterization, confirmed the presence of these in emblica juice. Electric field strength of 22 kV cm^?1 was found to be optimum, where maximum cell disintegration index (0.79) was achieved during treatment time of 500 µs, which enhanced the amount of quercetin to about ninefolds and ellagic acid to about twofolds respectively, in comparison to untreated and thermally treated juice sample. However, a reverse trend was observed in thermally treated juice where degradation of the compounds (p < 0.05) was detected. Thus, PEF can be considered as a viable medium for extracting intracellular metabolites, thereby incrementing the functional potential of emblica juice.     

A Rapid and Specific Biosensor for <Emphasis Type="Italic">Salmonella</Emphasis> Typhimurium Detection in Milk

This paper reports the application of an amperometric biosensor for rapid and specific Salmonella Typhimurium detection in milk. This device was developed from self-assembled monolayer technique on a gold screen-printed electrode, using cysteamine thiol. Polyclonal antibodies were oriented by protein A immobilization. The biosensor structure was characterized by cyclic voltammetry, Fourier transform infrared spectroscopy, and scanning electron microscopy. The analytical response was obtained by a chronoamperometry technique, using a direct-sandwich peroxidase-labeled system. The biosensor device showed a qualitative behavior with a very low limit of detection of 10 CFU mL^?1 and a detection time of 125 min. The biosensor specificity was demonstrated in pure and mixed samples with strains of Escherichia coli and Citrobacter freundii. The performance of the biosensor was found satisfactory, and the device was tested in skimmed and whole milk samples, being able to detect S. Typhimurium quickly, without an enrichment step. This structure of immunosensor assembly can be expended in future studies for other food matrices and bacterial species, making it a useful tool to ensure food safety.     

Magnetoelastic biosensor for the detection of Salmonella typhimurium in food products

In this article, a magnetoelastic sensor immobilized with polyclonal antibody for the detection of Salmonella typhimurium in food products is described. The remote query nature of magnetoelastic sensors enables the detection of bacterial species in sealed and opaque containers. Bacterial binding to the antibody on the sensor surfaces changed the resonance parameters, and these changes were quantified by the shift in the sensor’s resonance frequency. Response of the sensors to increasing concentrations (5 × 10¹–5 × 10⁸ cfu/ml) of S. typhimurium in three different food products (water, fat-free milk and apple juice) was studied and similar responses were observed. These results were also further ascertained by Scanning Electron Microscopy (SEM) studies. A detection limit of 5 × 10³ cfu/ml, with a sensitivity of 139 Hz/decade was obtained for the sensors tested in water samples, as compared to 129 Hz/decade in apple juice and 127 Hz/decade in fat free milk. A 2 × 0.4 × 0.015 mm sensor was employed in all the investigations. The dissociation constant K _d and the binding valencies for S. typhimurium spiked in water samples was 435 cfu/ml and 2.33 respectively; as compared to 309 cfu/ml and 2.38 for apple juice; and 1389 cfu/ml and 1.85 for fat free milk samples. Bacterial binding was specific and a divalent binding was observed.     

Simultaneous Detection of Salmonella,Listeria monocytogenes,and Staphylococcus aureus by Multiplex Real-Time PCR Assays Using High-Resolution Melting

A method combining multiplex real-time polymerase chain reaction (PCR) with high-resolution melting (HRM) analysis for rapid and specific simultaneous detection of Salmonella, Listeria monocytogenes, and Staphylococcus aureus was developed. The method included a melting-curve analysis of products and was evaluated by specificity, sensitivity and reproducibility analyses. Sensitivity and reproducibility analyses was both conducted by genomic DNA extracted from serial dilutions for each target pathogen. Assays with artificially inoculated and naturally contaminated samples after enrichment were also conducted. In the specificity test, there was no nonspecific amplification of the 44 nontarget pathogens, whereas the actual T _m values were 79.38?±?0.14, 82.54?±?0.15, and 77.36?±?0.14 °C for Salmonella, L. monocytogenes, and S. aureus, respectively. The sensitivity of the method was 3.5?×?10² CFU ml^?1 for Salmonella and L. monocytogenes and 3.5?×?10³ CFU ml^?1 for S. aureus. The coefficients of variation of T _m values ranged 0.51–1.03 % for Salmonella, 1.63–2.11 % for L. monocytogenes, and 0.75–2.17 % for S. aureus in intraassay, and ranged 0.81–2.43 % for Salmonella, 1.97–2.35 % for L. monocytogenes, and 0.93–3.93 % for S. aureus in interassay. The detection limit in artificially inoculated samples (n?=?50) was 5 CFU (25 g)^?1 food for the three tested pathogens. In the naturally contaminated samples (n?=?120),Salmonella DNA was detected by HRM, sequencing, and conventional culture-based methods at a positive rate of 25.00, 25.00, and 24.17 %, respectively; the corresponding rates for L. monocytogenes were 14.17, 14.17, and 14.17 %, respectively, while those for S. aureus were 16.7, 16.7, and 16.7 %, respectively.